ardupilot/libraries/AP_HAL_ChibiOS/UARTDriver.h

/*
 * 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
 */
#pragma once

#include <AP_HAL/utility/RingBuffer.h>

#include "AP_HAL_ChibiOS.h"
#include "shared_dma.h"
#include "Semaphores.h"

#define RX_BOUNCE_BUFSIZE 128
#define TX_BOUNCE_BUFSIZE 64

#define UART_MAX_DRIVERS 7

class ChibiOS::UARTDriver : public AP_HAL::UARTDriver {
public:
    UARTDriver(uint8_t serial_num);

    void begin(uint32_t b);
    void begin(uint32_t b, uint16_t rxS, uint16_t txS);
    void end();
    void flush();
    bool is_initialized();
    void set_blocking_writes(bool blocking);
    bool tx_pending();


    uint32_t available() override;
    uint32_t txspace() override;
    int16_t read() override;
    void _timer_tick(void) override;

    size_t write(uint8_t c);
    size_t write(const uint8_t *buffer, size_t size);

    // lock a port for exclusive use. Use a key of 0 to unlock
    bool lock_port(uint32_t key) override;

    // write to a locked port. If port is locked and key is not correct then 0 is returned
    // and write is discarded
    size_t write_locked(const uint8_t *buffer, size_t size, uint32_t key) override;
    
    struct SerialDef {
        BaseSequentialStream* serial;
        bool is_usb;
        bool dma_rx;
        uint8_t dma_rx_stream_id;
        uint32_t dma_rx_channel_id;
        bool dma_tx;
        uint8_t dma_tx_stream_id;
        uint32_t dma_tx_channel_id; 
        ioline_t rts_line;
        uint8_t get_index(void) const {
            return uint8_t(this - &_serial_tab[0]);
        }
    };

    bool wait_timeout(uint16_t n, uint32_t timeout_ms) override;

    void set_flow_control(enum flow_control flow_control) override;
    enum flow_control get_flow_control(void) override { return _flow_control; }

    // allow for low latency writes
    bool set_unbuffered_writes(bool on) override;

    void configure_parity(uint8_t v) override;
    void set_stop_bits(int n) override;

    /*
      return timestamp estimate in microseconds for when the start of
      a nbytes packet arrived on the uart. This should be treated as a
      time constraint, not an exact time. It is guaranteed that the
      packet did not start being received after this time, but it
      could have been in a system buffer before the returned time.

      This takes account of the baudrate of the link. For transports
      that have no baudrate (such as USB) the time estimate may be
      less accurate.

      A return value of zero means the HAL does not support this API
     */
    uint64_t receive_time_constraint_us(uint16_t nbytes) override;
    
private:
    bool tx_bounce_buf_ready;
    const SerialDef &sdef;

    // thread used for all UARTs
    static thread_t *uart_thread_ctx;

    // last time we ran the uart thread
    static uint32_t last_thread_run_us;
    
    // table to find UARTDrivers from serial number, used for event handling
    static UARTDriver *uart_drivers[UART_MAX_DRIVERS];

    // index into uart_drivers table
    uint8_t serial_num;

    // key for a locked port
    uint32_t lock_key;
    
    uint32_t _baudrate;
    uint16_t tx_len;
#if HAL_USE_SERIAL == TRUE
    SerialConfig sercfg;
#endif
    const thread_t* _uart_owner_thd;

    struct {
        // thread waiting for data
        thread_t *thread_ctx;
        // number of bytes needed
        uint16_t n;
    } _wait;

    // we use in-task ring buffers to reduce the system call cost
    // of ::read() and ::write() in the main loop
    uint8_t *rx_bounce_buf;
    uint8_t *tx_bounce_buf;
    ByteBuffer _readbuf{0};
    ByteBuffer _writebuf{0};
    Semaphore _write_mutex;
    const stm32_dma_stream_t* rxdma;
    const stm32_dma_stream_t* txdma;
    bool _in_timer;
    bool _blocking_writes;
    bool _initialised;
    bool _device_initialised;
    bool _lock_rx_in_timer_tick = false;
    Shared_DMA *dma_handle;
    static const SerialDef _serial_tab[];

    // timestamp for receiving data on the UART, avoiding a lock
    uint64_t _receive_timestamp[2];
    uint8_t _receive_timestamp_idx;

    // handling of flow control
    enum flow_control _flow_control = FLOW_CONTROL_DISABLE;
    bool _rts_is_active;
    uint32_t _last_write_completed_us;
    uint32_t _first_write_started_us;
    
    // set to true for unbuffered writes (low latency writes)
    bool unbuffered_writes;
    
    static void rx_irq_cb(void* sd);
    static void rxbuff_full_irq(void* self, uint32_t flags);
    static void tx_complete(void* self, uint32_t flags);

    void dma_tx_allocate(Shared_DMA *ctx);
    void dma_tx_deallocate(Shared_DMA *ctx);
    void update_rts_line(void);

    void check_dma_tx_completion(void);
    void write_pending_bytes_DMA(uint32_t n);
    void write_pending_bytes_NODMA(uint32_t n);
    void write_pending_bytes(void);

    void receive_timestamp_update(void);
    
    void thread_init();
    static void uart_thread(void *);
};