/*
 * This file is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Code by Andrew Tridgell and Siddharth Bharat Purohit
 * Bi-directional dshot based on Betaflight, code by Andy Piper and Siddharth Bharat Purohit
 */
#include "RCOutput.h"
#include <AP_Math/AP_Math.h>
#include <AP_BoardConfig/AP_BoardConfig.h>
#include <AP_HAL/utility/RingBuffer.h>
#include "GPIO.h"
#include "hwdef/common/stm32_util.h"
#include "hwdef/common/watchdog.h"
#include <AP_InternalError/AP_InternalError.h>
#include <AP_Vehicle/AP_Vehicle_Type.h>

#if HAL_USE_PWM == TRUE

using namespace ChibiOS;

extern const AP_HAL::HAL& hal;

#if HAL_WITH_IO_MCU
#include <AP_IOMCU/AP_IOMCU.h>
extern AP_IOMCU iomcu;
#endif

#define RCOU_SERIAL_TIMING_DEBUG 0

#if RCOU_DSHOT_TIMING_DEBUG
#define TOGGLE_PIN_DEBUG(pin) do { palToggleLine(HAL_GPIO_LINE_GPIO ## pin); } while (0)
#else
#define TOGGLE_PIN_DEBUG(pin) do {} while (0)
#endif

#define TELEM_IC_SAMPLE 16

struct RCOutput::pwm_group RCOutput::pwm_group_list[] = { HAL_PWM_GROUPS };
struct RCOutput::irq_state RCOutput::irq;
const uint8_t RCOutput::NUM_GROUPS = ARRAY_SIZE(RCOutput::pwm_group_list);

// event mask for triggering a PWM send
static const eventmask_t EVT_PWM_SEND  = EVENT_MASK(11);

// marker for a disabled channel
#define CHAN_DISABLED 255

// #pragma GCC optimize("Og")

/*
  initialise RC output driver
 */
void RCOutput::init()
{
    uint8_t pwm_count = AP_BoardConfig::get_pwm_count();
    for (auto &group : pwm_group_list) {
        const uint8_t i = &group - pwm_group_list;
        //Start Pwm groups
        group.current_mode = MODE_PWM_NORMAL;
        group.dshot_event_mask = EVENT_MASK(i);

        for (uint8_t j = 0; j < 4; j++ ) {
            uint8_t chan = group.chan[j];
            if (chan >= pwm_count) {
                group.chan[j] = CHAN_DISABLED;
            }
            if (group.chan[j] != CHAN_DISABLED) {
                num_fmu_channels = MAX(num_fmu_channels, group.chan[j]+1);
                group.ch_mask |= (1U<<group.chan[j]);
            }
#ifdef HAL_WITH_BIDIR_DSHOT
            group.bdshot.telem_tim_ch[j] = CHAN_DISABLED;
#endif
        }
        if (group.ch_mask != 0) {
            pwmStart(group.pwm_drv, &group.pwm_cfg);
            group.pwm_started = true;
        }
        chVTObjectInit(&group.dma_timeout);
    }

#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.init();
        // with IOMCU the local (FMU) channels start at 8
        chan_offset = 8;
    }
#endif
    chMtxObjectInit(&trigger_mutex);

    // setup default output rate of 50Hz
    set_freq(0xFFFF ^ ((1U<<chan_offset)-1), 50);

#ifdef HAL_GPIO_PIN_SAFETY_IN
    safety_state = AP_HAL::Util::SAFETY_DISARMED;
#endif

#if RCOU_DSHOT_TIMING_DEBUG
    hal.gpio->pinMode(54, 1);
    hal.gpio->pinMode(55, 1);
    hal.gpio->pinMode(56, 1);
    hal.gpio->pinMode(57, 1);
#endif

    _initialised = true;
}

/*
  thread for handling RCOutput send
 */
void RCOutput::rcout_thread()
{
    uint32_t last_thread_run_us = 0; // last time we did a 1kHz run of rcout

    rcout_thread_ctx = chThdGetSelfX();

    // don't start outputting until fully configured
    while (!hal.scheduler->is_system_initialized()) {
        hal.scheduler->delay_microseconds(1000);
    }

    while (true) {
        const uint32_t period_us = AP_HAL::micros() - last_thread_run_us;
        if (period_us < 1000) {
            chEvtWaitOneTimeout(EVT_PWM_SEND, chTimeUS2I(1000 - period_us));
        }
        // start the clock
        last_thread_run_us = AP_HAL::micros();

        // main thread requested a new dshot send
        if (!serial_group) {
            // do a blocking send now, to guarantee DShot sends at
            // above 1000 Hz. This makes the protocol more reliable on
            // long cables, and also keeps some ESCs happy that don't
            // like low rates
            dshot_send_groups();
            // now unlock everything
            dshot_collect_dma_locks(last_thread_run_us);
        }

        // process any pending RC output requests
        timer_tick(last_thread_run_us);
    }
}

#ifndef HAL_NO_SHARED_DMA
// release locks on the groups that are pending in reverse order
void RCOutput::dshot_collect_dma_locks(uint32_t last_run_us)
{
    if (NUM_GROUPS == 0) {
        return;
    }
    for (int8_t i = NUM_GROUPS - 1; i >= 0; i--) {
        pwm_group &group = pwm_group_list[i];
        if (group.dma_handle != nullptr && group.dma_handle->is_locked()) {
            // calculate how long we have left
            const uint32_t deltat = AP_HAL::micros() - last_run_us;
            // if we have time left wait for the event
            eventmask_t mask = 0;
            if (deltat < 1000) {
                mask = chEvtWaitOneTimeout(group.dshot_event_mask, chTimeUS2I(1000 - deltat));
            }
            // no time left cancel and restart
            if (!mask) {
                dma_cancel(group);
            }
            group.dshot_waiter = nullptr;
#ifdef HAL_WITH_BIDIR_DSHOT
            // if using input capture DMA then clean up
            if (group.bdshot.enabled) {
                // the channel index only moves on with success
                const uint8_t chan = mask ? group.bdshot.prev_telem_chan
                    : group.bdshot.curr_telem_chan;
                // only unlock if not shared
                if (group.bdshot.ic_dma_handle[chan] != nullptr
                    && group.bdshot.ic_dma_handle[chan] != group.dma_handle) {
                    group.bdshot.ic_dma_handle[chan]->unlock();
                }
            }
#endif
            group.dma_handle->unlock();
        }
    }
}
#endif // HAL_NO_SHARED_DMA

/*
  setup the output frequency for a group and start pwm output
 */
void RCOutput::set_freq_group(pwm_group &group)
{
    if (mode_requires_dma(group.current_mode)) {
        // speed setup in DMA handler
        return;
    }

    uint16_t freq_set = group.rc_frequency;
    uint32_t old_clock = group.pwm_cfg.frequency;
    uint32_t old_period = group.pwm_cfg.period;

    if (freq_set > 400 || group.current_mode == MODE_PWM_ONESHOT125) {
        // use a 8MHz clock for higher frequencies or for
        // oneshot125. Using 8MHz for oneshot125 results in the full
        // 1000 steps for smooth output
        group.pwm_cfg.frequency = 8000000;
    } else if (freq_set <= 400) {
        // use a 1MHz clock
        group.pwm_cfg.frequency = 1000000;
    }

    // check if the frequency is possible, and keep halving
    // down to 1MHz until it is OK with the hardware timer we
    // are using. If we don't do this we'll hit an assert in
    // the ChibiOS PWM driver on some timers
    PWMDriver *pwmp = group.pwm_drv;
    uint32_t psc = (pwmp->clock / pwmp->config->frequency) - 1;
    while ((psc > 0xFFFF || ((psc + 1) * pwmp->config->frequency) != pwmp->clock) &&
           group.pwm_cfg.frequency > 1000000) {
        group.pwm_cfg.frequency /= 2;
        psc = (pwmp->clock / pwmp->config->frequency) - 1;
    }

    if (group.current_mode == MODE_PWM_ONESHOT ||
        group.current_mode == MODE_PWM_ONESHOT125) {
        // force a period of 0, meaning no pulses till we trigger
        group.pwm_cfg.period = 0;
    } else {
        group.pwm_cfg.period = group.pwm_cfg.frequency/freq_set;
    }

    bool force_reconfig = false;
    for (uint8_t j=0; j<4; j++) {
        if (group.pwm_cfg.channels[j].mode == PWM_OUTPUT_ACTIVE_LOW) {
            group.pwm_cfg.channels[j].mode = PWM_OUTPUT_ACTIVE_HIGH;
            force_reconfig = true;
        }
        if (group.pwm_cfg.channels[j].mode == PWM_COMPLEMENTARY_OUTPUT_ACTIVE_LOW) {
            group.pwm_cfg.channels[j].mode = PWM_COMPLEMENTARY_OUTPUT_ACTIVE_HIGH;
            force_reconfig = true;
        }

    }

    if (old_clock != group.pwm_cfg.frequency ||
        old_period != group.pwm_cfg.period ||
        !group.pwm_started ||
        force_reconfig) {
        // we need to stop and start to setup the new clock
        if (group.pwm_started) {
            pwmStop(group.pwm_drv);
        }
        pwmStart(group.pwm_drv, &group.pwm_cfg);
        group.pwm_started = true;
    }
    pwmChangePeriod(group.pwm_drv, group.pwm_cfg.period);
}

/*
  set output frequency in HZ for a set of channels given by a mask
 */
void RCOutput::set_freq(uint32_t chmask, uint16_t freq_hz)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        // change frequency on IOMCU
        uint16_t io_chmask = chmask & 0xFF;
        if (io_chmask) {
            // disallow changing frequency of this group if it is greater than the default
            for (uint8_t i=0; i<ARRAY_SIZE(iomcu.ch_masks); i++) {
                const uint16_t mask = io_chmask & iomcu.ch_masks[i];
                if (mask != 0) {
                    if (freq_hz > 50) {
                        io_fast_channel_mask |= mask;
                    } else {
                        io_fast_channel_mask &= ~mask;
                    }
                }
            }
            iomcu.set_freq(io_fast_channel_mask, freq_hz);
        }
    }
#endif

    // convert to a local (FMU) channel mask
    chmask >>= chan_offset;
    if (chmask == 0) {
        return;
    }

    /*
      we enable the new frequency on all groups that have one
      of the requested channels. This means we may enable high
      speed on some channels that aren't requested, but that
      is needed in order to fly a vehicle such as a hex
      multicopter properly
    */
    for (auto &group : pwm_group_list) {
        // greater than 400 doesn't give enough room at higher periods for
        // the down pulse. This still allows for high rate with oneshot and dshot.
        uint16_t group_freq = freq_hz;
        if (group_freq > 400 && group.current_mode != MODE_PWM_BRUSHED) {
            group_freq = 400;
        }
        if ((group.ch_mask & chmask) != 0) {
            group.rc_frequency = group_freq;
            set_freq_group(group);
            // disallow changing frequency of this group if it is greater than the default
            if (group_freq > 50) {
                fast_channel_mask |= group.ch_mask;
            }
        }
    }
}

/*
  set default output rate
 */
void RCOutput::set_default_rate(uint16_t freq_hz)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.set_default_rate(freq_hz);
    }
#endif
    for (auto &group : pwm_group_list) {
        if ((group.ch_mask & fast_channel_mask) || group.ch_mask == 0) {
            // don't change fast channels
            continue;
        }
        group.pwm_cfg.period = group.pwm_cfg.frequency/freq_hz;
        if (group.pwm_started) {
            pwmChangePeriod(group.pwm_drv, group.pwm_cfg.period);
        }
    }
}

/*
  find pwm_group and index in group given a channel number
 */
RCOutput::pwm_group *RCOutput::find_chan(uint8_t chan, uint8_t &group_idx)
{
    if (chan >= max_channels) {
        return nullptr;
    }
    if (chan < chan_offset) {
        return nullptr;
    }
    chan -= chan_offset;

    for (auto &group : pwm_group_list) {
        for (uint8_t j = 0; j < 4; j++) {
            if (group.chan[j] == chan) {
                group_idx = j;
                return &group;
            }
        }
    }
    return nullptr;
}

uint16_t RCOutput::get_freq(uint8_t chan)
{
#if HAL_WITH_IO_MCU
    if (chan < chan_offset) {
        return iomcu.get_freq(chan);
    }
#endif
    uint8_t i;
    pwm_group *grp = find_chan(chan, i);
    if (grp) {
        return grp->pwm_drv->config->frequency / grp->pwm_drv->period;
    }
    // assume 50Hz default
    return 50;
}

void RCOutput::enable_ch(uint8_t chan)
{
    uint8_t i;
    pwm_group *grp = find_chan(chan, i);
    if (grp) {
        en_mask |= 1U << (chan - chan_offset);
    }
}

void RCOutput::disable_ch(uint8_t chan)
{
    uint8_t i;
    pwm_group *grp = find_chan(chan, i);
    if (grp) {
        pwmDisableChannel(grp->pwm_drv, i);
        en_mask &= ~(1U<<(chan - chan_offset));
    }
}

void RCOutput::write(uint8_t chan, uint16_t period_us)
{
    if (chan >= max_channels) {
        return;
    }
    last_sent[chan] = period_us;

#if HAL_WITH_IO_MCU
    // handle IO MCU channels
    if (AP_BoardConfig::io_enabled()) {
        uint16_t io_period_us = period_us;
        if ((iomcu_mode == MODE_PWM_ONESHOT125) && ((1U<<chan) & io_fast_channel_mask)) {
            // the iomcu only has one oneshot setting, so we need to scale by a factor
            // of 8 here for oneshot125
            io_period_us /= 8;
        }
        iomcu.write_channel(chan, io_period_us);
    }
#endif
    if (chan < chan_offset) {
        return;
    }

    if (safety_state == AP_HAL::Util::SAFETY_DISARMED && !(safety_mask & (1U<<chan))) {
        // implement safety pwm value
        period_us = safe_pwm[chan];
    }

    chan -= chan_offset;

    period[chan] = period_us;

    if (chan < num_fmu_channels) {
        active_fmu_channels = MAX(chan+1, active_fmu_channels);
        if (!corked) {
            push_local();
        }
    }
}

/*
  push values to local channels from period[] array
 */
void RCOutput::push_local(void)
{
    if (active_fmu_channels == 0) {
        return;
    }
    uint16_t outmask = (1U<<active_fmu_channels)-1;
    outmask &= en_mask;

    uint16_t widest_pulse = 0;
    uint8_t need_trigger = 0;

    bool safety_on = hal.util->safety_switch_state() == AP_HAL::Util::SAFETY_DISARMED;
    for (auto &group : pwm_group_list) {
        if (serial_group) {
            continue;
        }
        if (!group.pwm_started) {
            continue;
        }
        for (uint8_t j = 0; j < 4; j++) {
            uint8_t chan = group.chan[j];
            if (chan == CHAN_DISABLED) {
                continue;
            }
            if (outmask & (1UL<<chan)) {
                uint32_t period_us = period[chan];

                if (safety_on && !(safety_mask & (1U<<(chan+chan_offset)))) {
                    // safety is on, overwride pwm
                    period_us = safe_pwm[chan+chan_offset];
                }

                if (group.current_mode == MODE_PWM_BRUSHED) {
                    if (period_us <= _esc_pwm_min) {
                        period_us = 0;
                    } else if (period_us >= _esc_pwm_max) {
                        period_us = PWM_FRACTION_TO_WIDTH(group.pwm_drv, 1, 1);
                    } else {
                        period_us = PWM_FRACTION_TO_WIDTH(group.pwm_drv,\
                               (_esc_pwm_max - _esc_pwm_min), (period_us - _esc_pwm_min));
                    }
                    pwmEnableChannel(group.pwm_drv, j, period_us);
                } else if (group.current_mode == MODE_PWM_ONESHOT125) {
                    // this gives us a width in 125 ns increments, giving 1000 steps over the 125 to 250 range
                    uint32_t width = ((group.pwm_cfg.frequency/1000000U) * period_us) / 8U;
                    pwmEnableChannel(group.pwm_drv, j, width);
                    // scale the period down so we don't delay for longer than we need to
                    period_us /= 8;
                }
                else if (group.current_mode < MODE_PWM_DSHOT150) {
                    uint32_t width = (group.pwm_cfg.frequency/1000000U) * period_us;
                    pwmEnableChannel(group.pwm_drv, j, width);
                }
#ifndef DISABLE_DSHOT
                else if (is_dshot_protocol(group.current_mode) || group.current_mode == MODE_NEOPIXEL || group.current_mode == MODE_PROFILED) {
                    // set period_us to time for pulse output, to enable very fast rates
                    period_us = group.dshot_pulse_time_us;
                }
#endif //#ifndef DISABLE_DSHOT
                if (period_us > widest_pulse) {
                    widest_pulse = period_us;
                }
                if (group.current_mode == MODE_PWM_ONESHOT ||
                    group.current_mode == MODE_PWM_ONESHOT125 ||
                    group.current_mode == MODE_NEOPIXEL ||
                    group.current_mode == MODE_PROFILED ||
                    is_dshot_protocol(group.current_mode)) {
                    const uint8_t i = &group - pwm_group_list;
                    need_trigger |= (1U<<i);
                }
            }
        }
    }

    if (widest_pulse > 2300) {
        widest_pulse = 2300;
    }
    trigger_widest_pulse = widest_pulse;

    trigger_groupmask = need_trigger;

    if (trigger_groupmask) {
        trigger_groups();
    }
}

uint16_t RCOutput::read(uint8_t chan)
{
    if (chan >= max_channels) {
        return 0;
    }
#if HAL_WITH_IO_MCU
    if (chan < chan_offset) {
        return iomcu.read_channel(chan);
    }
#endif
    chan -= chan_offset;
    return period[chan];
}

void RCOutput::read(uint16_t* period_us, uint8_t len)
{
    if (len > max_channels) {
        len = max_channels;
    }
#if HAL_WITH_IO_MCU
    for (uint8_t i=0; i<MIN(len, chan_offset); i++) {
        period_us[i] = iomcu.read_channel(i);
    }
#endif
    if (len <= chan_offset) {
        return;
    }
    len -= chan_offset;
    period_us += chan_offset;

    memcpy(period_us, period, len*sizeof(uint16_t));
}

uint16_t RCOutput::read_last_sent(uint8_t chan)
{
    if (chan >= max_channels) {
        return 0;
    }
    return last_sent[chan];
}

void RCOutput::read_last_sent(uint16_t* period_us, uint8_t len)
{
    if (len > max_channels) {
        len = max_channels;
    }
    for (uint8_t i=0; i<len; i++) {
        period_us[i] = read_last_sent(i);
    }
}

/*
  does an output mode require the use of the UP DMA channel?
 */
bool RCOutput::mode_requires_dma(enum output_mode mode) const
{
#ifdef DISABLE_DSHOT
    return false;
#else
    return is_dshot_protocol(mode) || (mode == MODE_NEOPIXEL) || (mode == MODE_PROFILED);
#endif //#ifdef DISABLE_DSHOT
}

/*
  setup a group for DMA output at a given bitrate. The bit_width is
  the value for a pulse width in the DMA buffer for a full bit.

  This is used for both DShot and serial output
 */
bool RCOutput::setup_group_DMA(pwm_group &group, uint32_t bitrate, uint32_t bit_width, bool active_high, const uint16_t buffer_length, bool choose_high,
    uint32_t pulse_time_us)
{
#ifndef DISABLE_DSHOT
    // for dshot we setup for DMAR based output
    if (!group.dma_handle) {
        group.dma_handle = new Shared_DMA(group.dma_up_stream_id, SHARED_DMA_NONE,
                                          FUNCTOR_BIND_MEMBER(&RCOutput::dma_allocate, void, Shared_DMA *),
                                          FUNCTOR_BIND_MEMBER(&RCOutput::dma_deallocate, void, Shared_DMA *));
        if (!group.dma_handle) {
            return false;
        }
    }

    // hold the lock during setup, to ensure there isn't a DMA operation ongoing
    group.dma_handle->lock();
    if (!group.dma_buffer || buffer_length != group.dma_buffer_len) {
        if (group.dma_buffer) {
            hal.util->free_type(group.dma_buffer, group.dma_buffer_len, AP_HAL::Util::MEM_DMA_SAFE);
            group.dma_buffer_len = 0;
        }
        group.dma_buffer = (uint32_t *)hal.util->malloc_type(buffer_length, AP_HAL::Util::MEM_DMA_SAFE);
        if (!group.dma_buffer) {
            group.dma_handle->unlock();
            return false;
        }
        group.dma_buffer_len = buffer_length;
    }
    // reset the pulse time inside the lock
    group.dshot_pulse_time_us = pulse_time_us;

#ifdef HAL_WITH_BIDIR_DSHOT
    // configure input capture DMA if required
    if (is_bidir_dshot_enabled()) {
        if (!bdshot_setup_group_ic_DMA(group)) {
            group.dma_handle->unlock();
            return false;
        }
    }
#endif
    // configure timer driver for DMAR at requested rate
    if (group.pwm_started) {
        pwmStop(group.pwm_drv);
        group.pwm_started = false;
    }

    // adjust frequency to give an allowed value given the
    // clock. There is probably a better way to do this
    const uint32_t original_bitrate = bitrate;
    uint32_t freq = 0;
    uint32_t target_frequency = bitrate * bit_width;
    while (true) {
        uint32_t clock_hz = group.pwm_drv->clock;
        target_frequency = bitrate * bit_width;
        uint32_t prescaler = clock_hz / target_frequency;
        freq = clock_hz / prescaler;
        // hal.console->printf("CLOCK=%u BW=%u FREQ=%u PRE=%u BR=%u\n", clock_hz, bit_width, freq/bit_width, prescaler, bitrate);
        if (prescaler > 0x8000) {
            group.dma_handle->unlock();
            return false;
        }
        if (!choose_high) {
            break;
        }
        // we want to choose a frequency that gives at least the
        // target, erring on the high side not low side
        uint32_t actual_bitrate = freq / bit_width;
        if (actual_bitrate >= original_bitrate || bitrate < 10000) {
            break;
        }
        bitrate += 10000;
        if (bitrate >= 2 * original_bitrate) {
            break;
        }
    }

    group.pwm_cfg.frequency = freq;
    group.pwm_cfg.period = bit_width;
    group.pwm_cfg.dier = TIM_DIER_UDE;
    group.pwm_cfg.cr2 = 0;
    group.bit_width_mul = (freq + (target_frequency/2)) / target_frequency;

    for (uint8_t j=0; j<4; j++) {
        pwmmode_t mode = group.pwm_cfg.channels[j].mode;
        if (mode != PWM_OUTPUT_DISABLED) {
            if(mode == PWM_COMPLEMENTARY_OUTPUT_ACTIVE_LOW || mode == PWM_COMPLEMENTARY_OUTPUT_ACTIVE_HIGH) {
               group.pwm_cfg.channels[j].mode = active_high ? PWM_COMPLEMENTARY_OUTPUT_ACTIVE_HIGH : PWM_COMPLEMENTARY_OUTPUT_ACTIVE_LOW;
            } else {
               group.pwm_cfg.channels[j].mode = active_high ? PWM_OUTPUT_ACTIVE_HIGH : PWM_OUTPUT_ACTIVE_LOW;
            }
        }
    }

    pwmStart(group.pwm_drv, &group.pwm_cfg);
    group.pwm_started = true;

    for (uint8_t j=0; j<4; j++) {
        if (group.chan[j] != CHAN_DISABLED) {
            pwmEnableChannel(group.pwm_drv, j, 0);
        }
    }

    group.dma_handle->unlock();
    return true;
#else
    return false;
#endif //#ifndef DISABLE_DSHOT
}

/*
  setup output mode for a group, using group.current_mode. Used to restore output
  after serial operations
 */
void RCOutput::set_group_mode(pwm_group &group)
{
    if (group.pwm_started) {
        pwmStop(group.pwm_drv);
        group.pwm_started = false;
    }

    memset(group.bdshot.erpm, 0, 4*sizeof(uint16_t));

    switch (group.current_mode) {
    case MODE_PWM_BRUSHED:
        // force zero output initially
        for (uint8_t i=0; i<4; i++) {
            if (group.chan[i] == CHAN_DISABLED) {
                continue;
            }
            uint8_t chan = chan_offset + group.chan[i];
            write(chan, 0);
        }
        break;

    case MODE_NEOPIXEL:
    case MODE_PROFILED:
    {
        uint8_t bits_per_pixel = 24;
        bool active_high = true;

        if (group.current_mode == MODE_PROFILED) {
            bits_per_pixel = 25;
            active_high = false;
        }

        const uint32_t rate = protocol_bitrate(group.current_mode);
        const uint32_t bit_period = 20;

        // configure timer driver for DMAR at requested rate
        const uint8_t pad_end_bits = 8;
        const uint8_t pad_start_bits = 1;
        const uint8_t channels_per_group = 4;
        const uint16_t bit_length = bits_per_pixel * group.serial_nleds + pad_start_bits + pad_end_bits;
        const uint16_t buffer_length = bit_length * sizeof(uint32_t) * channels_per_group;
        // calculate min time between pulses taking into account the DMAR parallelism
        const uint32_t pulse_time_us = 1000000UL * bit_length / rate;

        if (!setup_group_DMA(group, rate, bit_period, active_high, buffer_length, true, pulse_time_us)) {
            group.current_mode = MODE_PWM_NONE;
            break;
        }
        break;
    }

    case MODE_PWM_DSHOT150 ... MODE_PWM_DSHOT1200: {
        const uint32_t rate = protocol_bitrate(group.current_mode);
        const uint32_t bit_period = 20;
        bool active_high = is_bidir_dshot_enabled() ? false : true;
        // calculate min time between pulses
        const uint32_t pulse_send_time_us = 1000000UL * dshot_bit_length / rate;

        // configure timer driver for DMAR at requested rate
        if (!setup_group_DMA(group, rate, bit_period, active_high,
            MAX(DSHOT_BUFFER_LENGTH, GCR_TELEMETRY_BUFFER_LEN), false, pulse_send_time_us)) {
            group.current_mode = MODE_PWM_NORMAL;
            break;
        }
        if (is_bidir_dshot_enabled()) {
            group.dshot_pulse_send_time_us = pulse_send_time_us;
            // to all intents and purposes the pulse time of send and receive are the same
            group.dshot_pulse_time_us = pulse_send_time_us + pulse_send_time_us + 30;
        }
        break;
    }

    case MODE_PWM_ONESHOT:
    case MODE_PWM_ONESHOT125:
        // for oneshot we set a period of 0, which results in no pulses till we trigger
        group.pwm_cfg.period = 0;
        group.rc_frequency = 1;
        if (group.pwm_started) {
            pwmChangePeriod(group.pwm_drv, group.pwm_cfg.period);
        }
        break;

    case MODE_PWM_NORMAL:
    case MODE_PWM_NONE:
        // nothing needed
        break;
    }

    set_freq_group(group);

    if (group.current_mode != MODE_PWM_NONE &&
        !group.pwm_started) {
        pwmStart(group.pwm_drv, &group.pwm_cfg);
        group.pwm_started = true;
        for (uint8_t j=0; j<4; j++) {
            if (group.chan[j] != CHAN_DISABLED) {
                pwmEnableChannel(group.pwm_drv, j, 0);
            }
        }
    }
}

/*
  setup output mode
 */
void RCOutput::set_output_mode(uint16_t mask, const enum output_mode mode)
{
    for (auto &group : pwm_group_list) {
        enum output_mode thismode = mode;
        if (((group.ch_mask << chan_offset) & mask) == 0) {
            // this group is not affected
            continue;
        }
        if (mode_requires_dma(thismode) && !group.have_up_dma) {
            thismode = MODE_PWM_NORMAL;
        }
        if (mode > MODE_PWM_NORMAL) {
            fast_channel_mask |= group.ch_mask;
        }
        // setup of the group mode also sets up DMA which might have changed, so always
        // redo it if using DMA
        if (group.current_mode != thismode) {
            group.current_mode = thismode;
            set_group_mode(group);
        }
    }
#if HAL_WITH_IO_MCU
    if ((mode == MODE_PWM_ONESHOT ||
         mode == MODE_PWM_ONESHOT125) &&
        (mask & ((1U<<chan_offset)-1)) &&
        AP_BoardConfig::io_enabled()) {
        iomcu_mode = mode;
        // also setup IO to use a 1Hz frequency, so we only get output
        // when we trigger
        iomcu.set_freq(io_fast_channel_mask, 1);
        iomcu.set_oneshot_mode();
        return;
    }
    if (mode == MODE_PWM_BRUSHED &&
        (mask & ((1U<<chan_offset)-1)) &&
        AP_BoardConfig::io_enabled()) {
        iomcu_mode = mode;
        iomcu.set_brushed_mode();
        return;
    }
#endif
}

/*
 * get output mode banner to inform user of how outputs are configured
 */
bool RCOutput::get_output_mode_banner(char banner_msg[], uint8_t banner_msg_len) const
{
    // create array of each channel's mode
    output_mode ch_mode[chan_offset + NUM_GROUPS * ARRAY_SIZE(pwm_group::chan)] = {};
    bool have_nonzero_modes = false;

#if HAL_WITH_IO_MCU
    // fill in ch_mode array for IOMCU channels
    if (AP_BoardConfig::io_enabled()) {
        for (uint8_t i = 0; i < chan_offset; i++ ) {
            ch_mode[i] = iomcu_mode;
        }
        have_nonzero_modes = (chan_offset > 0) && (iomcu_mode != MODE_PWM_NONE);
    }
#endif

    // fill in ch_mode array for FMU channels
    for (auto &group : pwm_group_list) {
        if (group.current_mode != MODE_PWM_NONE) {
            for (uint8_t j = 0; j < ARRAY_SIZE(group.chan); j++) {
                if (group.chan[j] != CHAN_DISABLED) {
                    const uint8_t chan_num = group.chan[j] + chan_offset;
                    if (chan_num < ARRAY_SIZE(ch_mode)) {
                        ch_mode[chan_num] = group.current_mode;
                        have_nonzero_modes = true;
                    }
                }
            }
        }
    }

    // handle simple case
    if (!have_nonzero_modes) {
        hal.util->snprintf(banner_msg, banner_msg_len, "RCOut: None");
        return true;
    }

    // write banner to banner_msg
    hal.util->snprintf(banner_msg, banner_msg_len, "RCOut:");
    uint8_t curr_mode_lowest_ch = 0;
    for (uint8_t k = 1; k < ARRAY_SIZE(ch_mode); k++) {
        if (ch_mode[k-1] != ch_mode[k]) {
            if (ch_mode[k-1] != MODE_PWM_NONE) {
                append_to_banner(banner_msg, banner_msg_len, ch_mode[k-1], curr_mode_lowest_ch + 1, k);
            }
            curr_mode_lowest_ch = k;
        }
    }

    // add final few channel's mode to banner (won't have been done by above loop)
    const uint8_t final_index = ARRAY_SIZE(ch_mode)-1;
    if (ch_mode[final_index] != MODE_PWM_NONE) {
        append_to_banner(banner_msg, banner_msg_len, ch_mode[final_index], curr_mode_lowest_ch + 1, final_index + 1);
    }

    return true;
}

/*
  start corking output
 */
void RCOutput::cork(void)
{
    corked = true;
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.cork();
    }
#endif
}

/*
  stop corking output
 */
void RCOutput::push(void)
{
    corked = false;
    push_local();
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.push();
    }
#endif
}

/*
  enable sbus output
 */
bool RCOutput::enable_px4io_sbus_out(uint16_t rate_hz)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        return iomcu.enable_sbus_out(rate_hz);
    }
#endif
    return false;
}

/*
  trigger output groups for oneshot or dshot modes
 */
void RCOutput::trigger_groups(void)
{
    if (!chMtxTryLock(&trigger_mutex)) {
        return;
    }
    uint64_t now = AP_HAL::micros64();
    if (now < min_pulse_trigger_us) {
        // guarantee minimum pulse separation
        hal.scheduler->delay_microseconds(min_pulse_trigger_us - now);
    }

    osalSysLock();
    for (auto &group : pwm_group_list) {
        if (irq.waiter) {
            // doing serial output, don't send pulses
            continue;
        }
        if (group.current_mode == MODE_PWM_ONESHOT ||
            group.current_mode == MODE_PWM_ONESHOT125) {
            const uint8_t i = &group - pwm_group_list;
            if (trigger_groupmask & (1U<<i)) {
                // this triggers pulse output for a channel group
                group.pwm_drv->tim->EGR = STM32_TIM_EGR_UG;
            }
        }
    }
    osalSysUnlock();
#ifndef HAL_NO_RCOUT_THREAD
    // trigger a PWM send
    if (!serial_group && hal.scheduler->in_main_thread()) {
        chEvtSignal(rcout_thread_ctx, EVT_PWM_SEND);
    }
#endif
    /*
      calculate time that we are allowed to trigger next pulse
      to guarantee at least a 50us gap between pulses
    */
    min_pulse_trigger_us = AP_HAL::micros64() + trigger_widest_pulse + 50;

    chMtxUnlock(&trigger_mutex);
}

/*
  periodic timer. This is used for oneshot and dshot modes, plus for
  safety switch update. Runs every 1000us.
 */
void RCOutput::timer_tick(uint32_t last_run_us)
{
    safety_update();

    if (serial_group) {
        return;
    }

    // if we have enough time left send out LED data
    if (serial_led_pending && AP_HAL::micros() - last_run_us < 500) {
        serial_led_pending = false;
        for (auto &group : pwm_group_list) {
            serial_led_pending |= !serial_led_send(group);
        }

        // release locks on the groups that are pending in reverse order
        dshot_collect_dma_locks(last_run_us);
    }

    if (min_pulse_trigger_us == 0) {
        return;
    }

    uint32_t now = AP_HAL::micros();

    if (now > min_pulse_trigger_us &&
        now - min_pulse_trigger_us > 4000) {
        // trigger at a minimum of 250Hz
        trigger_groups();
    }
}

// send dshot for all groups that support it
void RCOutput::dshot_send_groups()
{
    if (serial_group) {
        return;
    }

    // actually do a dshot send
    for (auto &group : pwm_group_list) {
        if (group.can_send_dshot_pulse()) {
            dshot_send(group);
            // delay sending the next group by the same amount as the IRQ dead time
            // to avoid irq collisions
            if (group.bdshot.enabled) {
                hal.scheduler->delay_microseconds(10U);
            }
        }
    }
}

/*
  allocate DMA channel
 */
void RCOutput::dma_allocate(Shared_DMA *ctx)
{
    for (auto &group : pwm_group_list) {
        if (group.dma_handle == ctx && group.dma == nullptr) {
            chSysLock();
            group.dma = dmaStreamAllocI(group.dma_up_stream_id, 10, dma_up_irq_callback, &group);
            chSysUnlock();
#if STM32_DMA_SUPPORTS_DMAMUX
            if (group.dma) {
                dmaSetRequestSource(group.dma, group.dma_up_channel);
            }
#endif
        }
    }
}

/*
  deallocate DMA channel
 */
void RCOutput::dma_deallocate(Shared_DMA *ctx)
{
    for (auto &group : pwm_group_list) {
        if (group.dma_handle == ctx && group.dma != nullptr) {
            chSysLock();
            dmaStreamFreeI(group.dma);
            group.dma = nullptr;
            chSysUnlock();
        }
    }
}

/*
  create a DSHOT 16 bit packet. Based on prepareDshotPacket from betaflight
 */
uint16_t RCOutput::create_dshot_packet(const uint16_t value, bool telem_request, bool bidir_telem)
{
    uint16_t packet = (value << 1);

    if (telem_request) {
        packet |= 1;
    }

    // compute checksum
    uint16_t csum = 0;
    uint16_t csum_data = packet;
    for (uint8_t i = 0; i < 3; i++) {
        csum ^= csum_data;
        csum_data >>= 4;
    }
    // trigger bi-dir dshot telemetry
    if (bidir_telem) {
        csum = ~csum;
    }

    // append checksum
    csum &= 0xf;
    packet = (packet << 4) | csum;

    return packet;
}

/*
  fill in a DMA buffer for dshot
 */
void RCOutput::fill_DMA_buffer_dshot(uint32_t *buffer, uint8_t stride, uint16_t packet, uint16_t clockmul)
{
    const uint32_t DSHOT_MOTOR_BIT_0 = 7 * clockmul;
    const uint32_t DSHOT_MOTOR_BIT_1 = 14 * clockmul;
    uint16_t i = 0;
    for (; i < dshot_pre; i++) {
        buffer[i * stride] = 0;
    }
    for (; i < 16 + dshot_pre; i++) {
        buffer[i * stride] = (packet & 0x8000) ? DSHOT_MOTOR_BIT_1 : DSHOT_MOTOR_BIT_0;
        packet <<= 1;
    }
    for (; i<dshot_bit_length; i++) {
        buffer[i * stride] = 0;
    }
}

/*
  send a set of DShot packets for a channel group
  This call be called in blocking mode from the timer, in which case it waits for the DMA lock.
  In normal operation it doesn't wait for the DMA lock.
 */
void RCOutput::dshot_send(pwm_group &group)
{
#ifndef DISABLE_DSHOT
    if (irq.waiter || (group.dshot_state != DshotState::IDLE && group.dshot_state != DshotState::RECV_COMPLETE)) {
        // doing serial output or DMAR input, don't send DShot pulses
        return;
    }

    // first make sure we have the DMA channel before anything else
    osalDbgAssert(!group.dma_handle->is_locked(), "DMA handle is already locked");
    group.dma_handle->lock();
    // only the timer thread releases the locks
    group.dshot_waiter = rcout_thread_ctx;
#ifdef HAL_WITH_BIDIR_DSHOT
    // assume that we won't be able to get the input capture lock
    group.bdshot.enabled = false;

    // now grab the input capture lock if we are able, we can only enable bi-dir on a group basis
    if (((_bdshot.mask & group.ch_mask) == group.ch_mask) && group.has_ic()) {
        if (group.has_shared_ic_up_dma()) {
            // no locking required
            group.bdshot.enabled = true;
        } else {
            osalDbgAssert(!group.bdshot.ic_dma_handle[group.bdshot.curr_telem_chan]->is_locked(), "DMA handle is already locked");
            group.bdshot.ic_dma_handle[group.bdshot.curr_telem_chan]->lock();
            group.bdshot.enabled = true;
        }
    }

    // if the last transaction returned telemetry, decode it
    if (group.dshot_state == DshotState::RECV_COMPLETE) {
        uint8_t chan = group.chan[group.bdshot.prev_telem_chan];
        uint32_t now = AP_HAL::millis();
        if (bdshot_decode_dshot_telemetry(group, group.bdshot.prev_telem_chan)) {
            _bdshot.erpm_clean_frames[chan]++;
        } else {
            _bdshot.erpm_errors[chan]++;
        }
        // reset statistics periodically
        if (now - _bdshot.erpm_last_stats_ms[chan] > 5000) {
            _bdshot.erpm_clean_frames[chan] = 0;
            _bdshot.erpm_errors[chan] = 0;
            _bdshot.erpm_last_stats_ms[chan] = now;
        }
    }

    if (group.bdshot.enabled) {
        if (group.pwm_started) {
            pwmStop(group.pwm_drv);
        }
        pwmStart(group.pwm_drv, &group.pwm_cfg);
        group.pwm_started = true;

        // we can be more precise for capture timer
        group.bdshot.telempsc = (uint16_t)(lrintf(((float)group.pwm_drv->clock / bdshot_get_output_rate_hz(group.current_mode) + 0.01f)/TELEM_IC_SAMPLE) - 1);
    }
#endif
    bool safety_on = hal.util->safety_switch_state() == AP_HAL::Util::SAFETY_DISARMED;

    memset((uint8_t *)group.dma_buffer, 0, DSHOT_BUFFER_LENGTH);

    for (uint8_t i=0; i<4; i++) {
        uint8_t chan = group.chan[i];
        if (chan != CHAN_DISABLED) {
            // retrieve the last erpm values
            _bdshot.erpm[chan] = group.bdshot.erpm[i];

            uint16_t pwm = period[chan];

            if (safety_on && !(safety_mask & (1U<<(chan+chan_offset)))) {
                // safety is on, overwride pwm
                pwm = safe_pwm[chan+chan_offset];
            }

            const uint16_t chan_mask = (1U<<chan);
            if (pwm == 0) {
                // no output
                continue;
            }

            pwm = constrain_int16(pwm, 1000, 2000);
            uint16_t value = 2 * (pwm - 1000);

            if (chan_mask & (reversible_mask>>chan_offset)) {
                // this is a DShot-3D output, map so that 1500 PWM is zero throttle reversed
                if (value < 1000) {
                    value = 2000 - value;
                } else if (value > 1000) {
                    value = value - 1000;
                } else {
                    // mid-throttle is off
                    value = 0;
                }
            }
            if (value != 0) {
                // dshot values are from 48 to 2047. Zero means off.
                value += 47;
            }

            bool request_telemetry = (telem_request_mask & chan_mask)?true:false;
            uint16_t packet = create_dshot_packet(value, request_telemetry, group.bdshot.enabled);
            if (request_telemetry) {
                telem_request_mask &= ~chan_mask;
            }
            fill_DMA_buffer_dshot(group.dma_buffer + i, 4, packet, group.bit_width_mul);
        }
    }

    chEvtGetAndClearEvents(group.dshot_event_mask);
    // start sending the pulses out
    send_pulses_DMAR(group, DSHOT_BUFFER_LENGTH);
#endif //#ifndef DISABLE_DSHOT
}

/*
  send a set of Serial LED packets for a channel group
  return true if send was successful
 */
bool RCOutput::serial_led_send(pwm_group &group)
{
    if (!group.serial_led_pending
        || (group.current_mode != MODE_NEOPIXEL && group.current_mode != MODE_PROFILED)) {
        return true;
    }

#ifndef DISABLE_DSHOT
    if (irq.waiter || !group.dma_handle->lock_nonblock()) {
        // doing serial output, don't send Serial LED pulses
        return false;
    }

    {
        WITH_SEMAPHORE(group.serial_led_mutex);

        group.serial_led_pending = false;
        group.prepared_send = false;

        // fill the DMA buffer while we have the lock
        fill_DMA_buffer_serial_led(group);
    }

    group.dshot_waiter = rcout_thread_ctx;

    chEvtGetAndClearEvents(group.dshot_event_mask);

    // start sending the pulses out
    send_pulses_DMAR(group, group.dma_buffer_len);
#endif //#ifndef DISABLE_DSHOT
    return true;
}


/*
  send a series of pulses for a group using DMAR. Pulses must have
  been encoded into the group dma_buffer with interleaving for the 4
  channels in the group
 */
void RCOutput::send_pulses_DMAR(pwm_group &group, uint32_t buffer_length)
{
#ifndef DISABLE_DSHOT
    osalDbgAssert(group.dma && group.dma_buffer, "DMA structures are corrupt");
    /*
      The DMA approach we are using is based on the DMAR method from
      betaflight. We use the TIMn_UP DMA channel for the timer, and
      setup an interleaved set of pulse durations, with a stride of 4
      (for the 4 channels). We use the DMAR register to point the DMA
      engine at the 4 CCR registers of the timer, so it fills in the
      pulse widths for each timer in turn. This means we only use a
      single DMA channel for groups of 4 timer channels. See the "DMA
      address for full transfer TIMx_DMAR" section of the
      datasheet. Many thanks to the betaflight developers for coming
      up with this great method.
     */
    TOGGLE_PIN_DEBUG(54);

    dmaStreamSetPeripheral(group.dma, &(group.pwm_drv->tim->DMAR));
    stm32_cacheBufferFlush(group.dma_buffer, buffer_length);
    dmaStreamSetMemory0(group.dma, group.dma_buffer);
    dmaStreamSetTransactionSize(group.dma, buffer_length/sizeof(uint32_t));
    dmaStreamSetFIFO(group.dma, STM32_DMA_FCR_DMDIS | STM32_DMA_FCR_FTH_FULL);
    dmaStreamSetMode(group.dma,
                     STM32_DMA_CR_CHSEL(group.dma_up_channel) |
                     STM32_DMA_CR_DIR_M2P | STM32_DMA_CR_PSIZE_WORD | STM32_DMA_CR_MSIZE_WORD |
                     STM32_DMA_CR_MINC | STM32_DMA_CR_PL(3) |
                     STM32_DMA_CR_TEIE | STM32_DMA_CR_TCIE);

    // setup for 4 burst strided transfers. 0x0D is the register
    // address offset of the CCR registers in the timer peripheral
    group.pwm_drv->tim->DCR = 0x0D | STM32_TIM_DCR_DBL(3);
    group.dshot_state = DshotState::SEND_START;

    TOGGLE_PIN_DEBUG(54);

    dmaStreamEnable(group.dma);
    // record when the transaction was started
    group.last_dmar_send_us = AP_HAL::micros64();
#endif //#ifndef DISABLE_DSHOT
}

/*
  unlock DMA channel after a dshot send completes and no return value is expected
 */
void RCOutput::dma_unlock(void *p)
{
    chSysLockFromISR();
    pwm_group *group = (pwm_group *)p;

    group->dshot_state = DshotState::IDLE;
    if (group->dshot_waiter != nullptr) {
        // tell the waiting process we've done the DMA. Note that
        // dshot_waiter can be null if we have cancelled the send
        chEvtSignalI(group->dshot_waiter, group->dshot_event_mask);
    }
    chSysUnlockFromISR();
}

#ifndef HAL_WITH_BIDIR_DSHOT
/*
  DMA interrupt handler. Used to mark DMA completed for DShot
 */
void RCOutput::dma_up_irq_callback(void *p, uint32_t flags)
{
    pwm_group *group = (pwm_group *)p;
    chSysLockFromISR();
    dmaStreamDisable(group->dma);
    if (group->in_serial_dma && irq.waiter) {
        // tell the waiting process we've done the DMA
        chEvtSignalI(irq.waiter, serial_event_mask);
    } else {
        // this prevents us ever having two dshot pulses too close together
        // dshot mandates a minimum pulse separation of 40us, WS2812 mandates 50us so we
        // pick the higher value
        chVTSetI(&group->dma_timeout, chTimeUS2I(50), dma_unlock, p);
    }
    chSysUnlockFromISR();
}
#endif

/*
  Cancel a DMA transaction in progress
 */
void RCOutput::dma_cancel(pwm_group& group)
{
    chSysLock();
    dmaStreamDisable(group.dma);
#ifdef HAL_WITH_BIDIR_DSHOT
    if (group.ic_dma_enabled()) {
        dmaStreamDisable(group.bdshot.ic_dma[group.bdshot.curr_telem_chan]);
    }
#endif
    chVTResetI(&group.dma_timeout);
    chEvtGetAndClearEventsI(group.dshot_event_mask);
    group.dshot_state = DshotState::IDLE;
    chSysUnlock();
}

/*
  setup for serial output to an ESC using the given
  baudrate. Assumes 1 start bit, 1 stop bit, LSB first and 8
  databits. This is used for passthrough ESC configuration and
  firmware flashing

  While serial output is active normal output to the channel group is
  suspended.
*/
bool RCOutput::serial_setup_output(uint8_t chan, uint32_t baudrate, uint16_t chanmask)
{
    // account for IOMCU channels
    chan -= chan_offset;
    chanmask >>= chan_offset;
    pwm_group *new_serial_group = nullptr;

    // find the channel group
    for (auto &group : pwm_group_list) {
        if (group.current_mode == MODE_PWM_BRUSHED) {
            // can't do serial output with brushed motors
            continue;
        }
        if (group.ch_mask & (1U<<chan)) {
            new_serial_group = &group;
            for (uint8_t j=0; j<4; j++) {
                if (group.chan[j] == chan) {
                    group.serial.chan = j;
                }
            }
            break;
        }
    }

    if (!new_serial_group) {
        if (serial_group) {
            // shutdown old group
            serial_end();
        }
        return false;
    }

    // stop further dshot output before we reconfigure the DMA
    serial_group = new_serial_group;

    // setup the groups for serial output. We ask for a bit width of 1, which gets modified by the
    // we setup all groups so they all are setup with the right polarity, and to make switching between
    // channels in blheli pass-thru fast
    for (auto &group : pwm_group_list) {
        if (group.ch_mask & chanmask) {
            if (!setup_group_DMA(group, baudrate, 10, false, DSHOT_BUFFER_LENGTH, false, 10)) {
                serial_end();
                return false;
            }
        }
    }

    // run the thread doing serial IO at highest priority. This is needed to ensure we don't
    // lose bytes when we switch between output and input
    serial_thread = chThdGetSelfX();
    serial_priority  = chThdGetSelfX()->realprio;
    chThdSetPriority(HIGHPRIO);

    // remember the bit period for serial_read_byte()
    serial_group->serial.bit_time_us = 1000000UL / baudrate;

    // remember the thread that set things up. This is also used to
    // mark the group as doing serial output, so normal output is
    // suspended
    irq.waiter = chThdGetSelfX();

    return true;
}


/*
  fill in a DMA buffer for a serial byte, assuming 1 start bit and 1 stop bit
 */
void RCOutput::fill_DMA_buffer_byte(uint32_t *buffer, uint8_t stride, uint8_t b, uint32_t bitval)
{
    const uint32_t BIT_0 = bitval;
    const uint32_t BIT_1 = 0;

    // start bit
    buffer[0] = BIT_0;

    // stop bit
    buffer[9*stride] = BIT_1;

    // 8 data bits
    for (uint8_t i = 0; i < 8; i++) {
        buffer[(1 + i) * stride] = (b & 1) ? BIT_1 : BIT_0;
        b >>= 1;
    }
}


/*
  send one serial byte, blocking call, should be called with the DMA lock held
*/
bool RCOutput::serial_write_byte(uint8_t b)
{
    chEvtGetAndClearEvents(serial_event_mask);

    fill_DMA_buffer_byte(serial_group->dma_buffer+serial_group->serial.chan, 4, b, serial_group->bit_width_mul*10);

    serial_group->in_serial_dma = true;

    // start sending the pulses out
    send_pulses_DMAR(*serial_group, 10*4*sizeof(uint32_t));

    // wait for the event
    eventmask_t mask = chEvtWaitAnyTimeout(serial_event_mask, chTimeMS2I(2));

    serial_group->in_serial_dma = false;

    return (mask & serial_event_mask) != 0;
}

/*
  send a set of serial bytes, blocking call
*/
bool RCOutput::serial_write_bytes(const uint8_t *bytes, uint16_t len)
{
#ifndef DISABLE_DSHOT
    if (!serial_group) {
        return false;
    }
    serial_group->dma_handle->lock();
    memset(serial_group->dma_buffer, 0, DSHOT_BUFFER_LENGTH);
    while (len--) {
        if (!serial_write_byte(*bytes++)) {
            serial_group->dma_handle->unlock();
            return false;
        }
    }

    // add a small delay for last word of output to have completely
    // finished
    hal.scheduler->delay_microseconds(25);

    serial_group->dma_handle->unlock();
    return true;
#else
    return false;
#endif // DISABLE_DSHOT
}

/*
  irq handler for bit transition in serial_read_byte()
  This implements a one byte soft serial reader
 */
void RCOutput::serial_bit_irq(void)
{
    systime_t now = chVTGetSystemTimeX();
    uint8_t bit = palReadLine(irq.line);
    bool send_signal = false;

#if RCOU_SERIAL_TIMING_DEBUG
    palWriteLine(HAL_GPIO_LINE_GPIO55, bit);
#endif

    if (irq.nbits == 0 || bit == irq.last_bit) {
        // start of byte, should be low
        if (bit != 0) {
            irq.byteval = 0x200;
            send_signal = true;
        } else {
            irq.nbits = 1;
            irq.byte_start_tick = now;
            irq.bitmask = 0;
        }
    } else {
        systime_t dt = now - irq.byte_start_tick;
        uint8_t bitnum = (dt+(irq.bit_time_tick/2)) / irq.bit_time_tick;

        if (bitnum > 10) {
            bitnum = 10;
        }
        if (!bit) {
            // set the bits that we've processed
            irq.bitmask |= ((1U<<bitnum)-1) & ~((1U<<irq.nbits)-1);
        }
        irq.nbits = bitnum;

        if (irq.nbits == 10) {
            send_signal = true;
            irq.byteval = irq.bitmask & 0x3FF;
            irq.bitmask = 0;
            irq.nbits = 1;
            irq.byte_start_tick = now;
        }
    }
    irq.last_bit = bit;

    if (send_signal) {
        chSysLockFromISR();
        chVTResetI(&irq.serial_timeout);
        chEvtSignalI(irq.waiter, serial_event_mask);
        chSysUnlockFromISR();
    }
}

/*
  timeout a byte read
 */
void RCOutput::serial_byte_timeout(void *ctx)
{
    chSysLockFromISR();
    irq.timed_out = true;
    chEvtSignalI((thread_t *)ctx, serial_event_mask);
    chSysUnlockFromISR();
}

/*
  read a byte from a port, using serial parameters from serial_setup_output()
*/
bool RCOutput::serial_read_byte(uint8_t &b)
{
    irq.timed_out = false;
    chVTSet(&irq.serial_timeout, chTimeMS2I(10), serial_byte_timeout, irq.waiter);
    bool timed_out = ((chEvtWaitAny(serial_event_mask) & serial_event_mask) == 0) || irq.timed_out;

    uint16_t byteval = irq.byteval;

    if (timed_out) {
        // we can accept a byte with a timeout if the last bit was 1
        // and the start bit is set correctly
        if (irq.last_bit == 0) {
            return false;
        }
        byteval = irq.bitmask | 0x200;
    }

    if ((byteval & 0x201) != 0x200) {
        // wrong start/stop bits
        return false;
    }

    b = uint8_t(byteval>>1);
    return true;
}

/*
  read a byte from a port, using serial parameters from serial_setup_output()
*/
uint16_t RCOutput::serial_read_bytes(uint8_t *buf, uint16_t len)
{
#ifndef DISABLE_SERIAL_ESC_COMM
    if (serial_group == nullptr) {
        return 0;
    }
    pwm_group &group = *serial_group;
    const ioline_t line = group.pal_lines[group.serial.chan];
    uint32_t gpio_mode = PAL_MODE_INPUT_PULLUP;
    uint32_t restore_mode = PAL_MODE_ALTERNATE(group.alt_functions[group.serial.chan]) | PAL_STM32_OSPEED_MID2 | PAL_STM32_OTYPE_PUSHPULL;
    uint16_t i = 0;

#if RCOU_SERIAL_TIMING_DEBUG
    hal.gpio->pinMode(54, 1);
    hal.gpio->pinMode(55, 1);
#endif

    // assume GPIO mappings for PWM outputs start at 50
    palSetLineMode(line, gpio_mode);

    chVTObjectInit(&irq.serial_timeout);
    chEvtGetAndClearEvents(serial_event_mask);

    irq.line = group.pal_lines[group.serial.chan];
    irq.nbits = 0;
    irq.bitmask = 0;
    irq.byteval = 0;
    irq.bit_time_tick = serial_group->serial.bit_time_us;
    irq.last_bit = 0;
    irq.waiter = chThdGetSelfX();

#if RCOU_SERIAL_TIMING_DEBUG
    palWriteLine(HAL_GPIO_LINE_GPIO54, 1);
#endif

    if (!((GPIO *)hal.gpio)->_attach_interrupt(line, serial_bit_irq, AP_HAL::GPIO::INTERRUPT_BOTH)) {
#if RCOU_SERIAL_TIMING_DEBUG
        palWriteLine(HAL_GPIO_LINE_GPIO54, 0);
#endif
        return false;
    }

    for (i=0; i<len; i++) {
        if (!serial_read_byte(buf[i])) {
            break;
        }
    }

    ((GPIO *)hal.gpio)->_attach_interrupt(line, nullptr, 0);
    irq.waiter = nullptr;

    palSetLineMode(line, restore_mode);
#if RCOU_SERIAL_TIMING_DEBUG
    palWriteLine(HAL_GPIO_LINE_GPIO54, 0);
#endif
    return i;
#else
    return false;
#endif //#ifndef DISABLE_SERIAL_ESC_COMM

}

/*
  end serial output
*/
void RCOutput::serial_end(void)
{
#ifndef DISABLE_SERIAL_ESC_COMM
    if (serial_group) {
        if (serial_thread == chThdGetSelfX()) {
            chThdSetPriority(serial_priority);
            serial_thread = nullptr;
        }
        irq.waiter = nullptr;
        for (uint8_t i = 0; i < NUM_GROUPS; i++ ) {
            pwm_group &group = pwm_group_list[i];
            // restore normal output
            if (group.pwm_started) {
                pwmStop(group.pwm_drv);
                group.pwm_started = false;
            }
            set_group_mode(group);
            set_freq_group(group);
        }
    }
    serial_group = nullptr;
#endif //#ifndef DISABLE_SERIAL_ESC_COMM
}

/*
  get safety switch state for Util.cpp
 */
AP_HAL::Util::safety_state RCOutput::_safety_switch_state(void)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        safety_state = iomcu.get_safety_switch_state();
    }
#endif
    if (!hal.util->was_watchdog_reset()) {
        hal.util->persistent_data.safety_state = safety_state;
    }
    return safety_state;
}

/*
  force the safety switch on, disabling PWM output from the IO board
*/
bool RCOutput::force_safety_on(void)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        return iomcu.force_safety_on();
    }
    return false;
#else
    safety_state = AP_HAL::Util::SAFETY_DISARMED;
    return true;
#endif
}

/*
  force the safety switch off, enabling PWM output from the IO board
*/
void RCOutput::force_safety_off(void)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.force_safety_off();
    }
#else
    safety_state = AP_HAL::Util::SAFETY_ARMED;
#endif
}

/*
  set PWM to send to a set of channels when the safety switch is
  in the safe state
*/
void RCOutput::set_safety_pwm(uint32_t chmask, uint16_t period_us)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.set_safety_pwm(chmask, period_us);
    }
#endif
    for (uint8_t i=0; i<16; i++) {
        if (chmask & (1U<<i)) {
            safe_pwm[i] = period_us;
        }
    }
}

/*
  update safety state
 */
void RCOutput::safety_update(void)
{
    uint32_t now = AP_HAL::millis();
    if (now - safety_update_ms < 100) {
        // update safety at 10Hz
        return;
    }
    safety_update_ms = now;

    AP_BoardConfig *boardconfig = AP_BoardConfig::get_singleton();

    if (boardconfig) {
        // remember mask of channels to allow with safety on
        safety_mask = boardconfig->get_safety_mask();
    }

#ifdef HAL_GPIO_PIN_SAFETY_IN
    // handle safety button
    bool safety_pressed = palReadLine(HAL_GPIO_PIN_SAFETY_IN);
    if (safety_pressed) {
        AP_BoardConfig *brdconfig = AP_BoardConfig::get_singleton();
        if (safety_press_count < 255) {
            safety_press_count++;
        }
        if (brdconfig && brdconfig->safety_button_handle_pressed(safety_press_count)) {
            if (safety_state ==AP_HAL::Util::SAFETY_ARMED) {
                safety_state = AP_HAL::Util::SAFETY_DISARMED;
            } else {
                safety_state = AP_HAL::Util::SAFETY_ARMED;
            }
        }
    } else {
        safety_press_count = 0;
    }
#elif HAL_WITH_IO_MCU
    safety_state = _safety_switch_state();
    iomcu.set_safety_mask(safety_mask);
#endif

#ifdef HAL_GPIO_PIN_LED_SAFETY
    led_counter = (led_counter+1) % 16;
    const uint16_t led_pattern = safety_state==AP_HAL::Util::SAFETY_DISARMED?0x5500:0xFFFF;
    palWriteLine(HAL_GPIO_PIN_LED_SAFETY, (led_pattern & (1U << led_counter))?0:1);
#endif
}

/*
  set PWM to send to a set of channels if the FMU firmware dies
*/
void RCOutput::set_failsafe_pwm(uint32_t chmask, uint16_t period_us)
{
#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        iomcu.set_failsafe_pwm(chmask, period_us);
    }
#endif
}

/*
  true when the output mode is of type dshot
*/
bool RCOutput::is_dshot_protocol(const enum output_mode mode)
{
    switch (mode) {
    case MODE_PWM_DSHOT150:
    case MODE_PWM_DSHOT300:
    case MODE_PWM_DSHOT600:
    case MODE_PWM_DSHOT1200:
        return true;
    default:
        return false;
    }
}

/*
    returns the bitrate in Hz of the given output_mode
*/
uint32_t RCOutput::protocol_bitrate(const enum output_mode mode)
{
    switch (mode) {
    case MODE_PWM_DSHOT150:
        return 150000;
    case MODE_PWM_DSHOT300:
        return 300000;
    case MODE_PWM_DSHOT600:
        return 600000;
    case MODE_PWM_DSHOT1200:
        return 1200000;
    case MODE_NEOPIXEL:
        return 800000;
    case MODE_PROFILED:
        return 1500000; // experiment winding this up 3000000 max from data sheet
    default:
        // use 1 to prevent a possible divide-by-zero
        return 1;
    }
}

/*
  setup serial led output for a given channel number, with
  the given max number of LEDs in the chain.
*/
bool RCOutput::set_serial_led_num_LEDs(const uint16_t chan, uint8_t num_leds, output_mode mode, uint16_t clock_mask)
{
    if (!_initialised) {
        return false;
    }

    uint8_t i = 0;
    pwm_group *grp = find_chan(chan, i);
    if (!grp) {
        return false;
    }

    // we must hold the LED mutex while resizing the array
    WITH_SEMAPHORE(grp->serial_led_mutex);
    // if already allocated a different size then return
    if ((grp->serial_nleds > 0 && num_leds != grp->serial_nleds)
         || (mode != MODE_NEOPIXEL && mode != MODE_PROFILED)) {
        return false;
    }
    // if already allocated this channel
    if (grp->serial_nleds > 0 && num_leds == grp->serial_nleds
        && grp->serial_led_data[i] != nullptr) {
        return false;
    }

    switch (mode) {
        case MODE_NEOPIXEL: {
            num_leds = MAX(num_leds, grp->serial_nleds);
            break;
        }
        case MODE_PROFILED: {
            // ProfiLED requires two dummy LED's to mark end of transmission
            num_leds = MAX(num_leds + 2, grp->serial_nleds);

            // Enable any clock channels in the same group
            grp->clock_mask = 0;
            for (uint8_t j = 0; j < 4; j++) {
                if ((clock_mask & (1U<<(grp->chan[j] + chan_offset))) != 0) {
                    grp->clock_mask |= 1U<<j;
                }
            }

            break;
        }
        default:
            return false;
    }

    // allocate the data storage array, since the group num_leds is changing
    /// we need to do all that are allocated
    if (grp->serial_nleds != num_leds || grp->serial_led_data[i] == nullptr) {
        for (uint8_t j = 0; j < 4; j++) {
            if (grp->serial_led_data[j] != nullptr) {
                delete[] grp->serial_led_data[j];
                grp->serial_led_data[j] = nullptr;
                if (num_leds > 0) {
                    grp->serial_led_data[j] = new SerialLed[num_leds];
                    if (grp->serial_led_data[j] == nullptr) {
                        num_leds = 0;
                    }
                }
            }
        }
        if (num_leds > 0 && grp->serial_led_data[i] == nullptr) {
            grp->serial_led_data[i] = new SerialLed[num_leds];
            if (grp->serial_led_data[i] == nullptr) {
                num_leds = 0;
            }
        }

        grp->serial_nleds = num_leds;
    }
    // at this point the group led data is all setup but the dma buffer still needs to be resized
    set_output_mode(1U<<chan, mode);

    return grp->current_mode == mode;
}

#pragma GCC push_options
#pragma GCC optimize("O2")
// Fill the group DMA buffer with data to be output
void RCOutput::fill_DMA_buffer_serial_led(pwm_group& group)
{
    memset(group.dma_buffer, 0, group.dma_buffer_len);
    for (uint8_t j = 0; j < 4; j++) {
        if (group.serial_led_data[j] == nullptr) {
            if (group.current_mode == MODE_PROFILED && (group.clock_mask & 1U<<j) != 0) {
                for (uint8_t i = 0; i < group.serial_nleds; i++) {
                    _set_profiled_clock(&group, j, i);
                }
            }
            continue;
        }

        for (uint8_t i = 0; i < group.serial_nleds; i++) {
            const SerialLed& led = group.serial_led_data[j][i];
            switch (group.current_mode) {
                case MODE_NEOPIXEL:
                    _set_neopixel_rgb_data(&group, j, i, led.red, led.green, led.blue);
                    break;
                case MODE_PROFILED: {
                    if (i < group.serial_nleds - 2) {
                        _set_profiled_rgb_data(&group, j, i, led.red, led.green, led.blue);
                    } else {
                        _set_profiled_blank_frame(&group, j, i);
                    }
                    break;
                }
                default:
                    break;
            }
        }
    }
}

/*
  setup neopixel (WS2812B) output data for a given output channel
  and a LED number. LED -1 is all LEDs
*/
void RCOutput::_set_neopixel_rgb_data(pwm_group *grp, uint8_t idx, uint8_t led, uint8_t red, uint8_t green, uint8_t blue)
{
    const uint8_t pad_start_bits = 1;
    const uint8_t neopixel_bit_length = 24;
    const uint8_t stride = 4;
    uint32_t *buf = grp->dma_buffer + (led * neopixel_bit_length + pad_start_bits) * stride + idx;
    uint32_t bits = (green<<16) | (red<<8) | blue;
    const uint32_t BIT_0 = 7 * grp->bit_width_mul;
    const uint32_t BIT_1 = 14 * grp->bit_width_mul;
    for (uint16_t b=0; b < 24; b++) {
        buf[b * stride] = (bits & 0x800000) ? BIT_1 : BIT_0;
        bits <<= 1;
    }
}

/*
  ProfiLED frame for a given output channel
  channel is active high and bits inverted to get clock rising edge away from data rising edge
*/
void RCOutput::_set_profiled_rgb_data(pwm_group *grp, uint8_t idx, uint8_t led, uint8_t red, uint8_t green, uint8_t blue)
{
    const uint8_t pad_start_bits = 1;
    const uint8_t bit_length = 25;
    const uint8_t stride = 4;
    uint32_t *buf = grp->dma_buffer + (led * bit_length + pad_start_bits) * stride + idx;
    uint32_t bits = 0x1000000 | (blue<<16) | (red<<8) | green;
    const uint32_t BIT_1 = 14 * grp->bit_width_mul;
    for (uint16_t b=0; b < bit_length; b++) {
        buf[b * stride] = (bits & 0x1000000) ? 0 : BIT_1;
        bits <<= 1;
    }
}

/*
  ProfiLED blank frame for a given output channel
  channel is active high and bits inverted to get clock rising edge away from data rising edge
*/
void RCOutput::_set_profiled_blank_frame(pwm_group *grp, uint8_t idx, uint8_t led)
{
    const uint8_t pad_start_bits = 1;
    const uint8_t bit_length = 25;
    const uint8_t stride = 4;
    uint32_t *buf = grp->dma_buffer + (led * bit_length + pad_start_bits) * stride + idx;
    const uint32_t BIT_1 = 14 * grp->bit_width_mul;
    for (uint16_t b=0; b < bit_length; b++) {
        buf[b * stride] = BIT_1;
    }
}

/*
  setup ProfiLED clock frame for a given output channel
*/
void RCOutput::_set_profiled_clock(pwm_group *grp, uint8_t idx, uint8_t led)
{
    const uint8_t pad_start_bits = 1;
    const uint8_t bit_length = 25;
    const uint8_t stride = 4;
    uint32_t *buf = grp->dma_buffer + (led * bit_length + pad_start_bits) * stride + idx;
    const uint32_t BIT_1 = 7 * grp->bit_width_mul;
    for (uint16_t b=0; b < bit_length; b++) {
        buf[b * stride] = BIT_1;
    }
}
#pragma GCC pop_options

/*
  setup serial LED output data for a given output channel
  and a LED number. LED -1 is all LEDs
*/
void RCOutput::set_serial_led_rgb_data(const uint16_t chan, int8_t led, uint8_t red, uint8_t green, uint8_t blue)
{
    if (!_initialised) {
        return;
    }

    uint8_t i = 0;
    pwm_group *grp = find_chan(chan, i);

    if (!grp) {
        return;
    }

    WITH_SEMAPHORE(grp->serial_led_mutex);

    if (grp->serial_nleds == 0 || led >= grp->serial_nleds
        || (grp->current_mode != MODE_NEOPIXEL && grp->current_mode != MODE_PROFILED)) {
        return;
    }

    if (led == -1) {
        grp->prepared_send = true;
        for (uint8_t n=0; n<grp->serial_nleds; n++) {
            serial_led_set_single_rgb_data(*grp, i, n, red, green, blue);
        }
        return;
    }

    // if not ouput clock and trailing frames, run through all LED's to do it now
    if (!grp->prepared_send) {
        grp->prepared_send = true;
        for (uint8_t n=0; n<grp->serial_nleds; n++) {
            serial_led_set_single_rgb_data(*grp, i, n, 0, 0, 0);
        }
    }
    serial_led_set_single_rgb_data(*grp, i, uint8_t(led), red, green, blue);
}

/*
  setup serial LED output data for a given output channel
  and a LED number. LED -1 is all LEDs
*/
void RCOutput::serial_led_set_single_rgb_data(pwm_group& group, uint8_t idx, uint8_t led, uint8_t red, uint8_t green, uint8_t blue)
{
    switch (group.current_mode) {
        case MODE_PROFILED:
        case MODE_NEOPIXEL:
            group.serial_led_data[idx][led].red = red;
            group.serial_led_data[idx][led].green = green;
            group.serial_led_data[idx][led].blue = blue;
            break;
        default:
            break;
    }
}

/*
  trigger send of serial led data for one group
*/
void RCOutput::serial_led_send(const uint16_t chan)
{
    if (!_initialised) {
        return;
    }

    uint8_t i;
    pwm_group *grp = find_chan(chan, i);
    if (!grp) {
        return;
    }

    WITH_SEMAPHORE(grp->serial_led_mutex);

    if (grp->serial_nleds == 0 || (grp->current_mode != MODE_NEOPIXEL && grp->current_mode != MODE_PROFILED)) {
        return;
    }

    if (grp->prepared_send) {
        grp->serial_led_pending = true;
        serial_led_pending = true;
    }
}

#endif // HAL_USE_PWM