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ardupilot/libraries/AP_RCProtocol/AP_RCProtocol_SBUS.cpp

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/*
SBUS decoder, based on src/modules/px4iofirmware/sbus.c from PX4Firmware
modified for use in AP_HAL_* by Andrew Tridgell
*/
/****************************************************************************
*
* Copyright (c) 2012-2014 PX4 Development Team. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/*
* 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
*/
#include "AP_RCProtocol_SBUS.h"
#define SBUS_FRAME_SIZE 25
#define SBUS_INPUT_CHANNELS 16
#define SBUS_FLAGS_BYTE 23
#define SBUS_FAILSAFE_BIT 3
#define SBUS_FRAMELOST_BIT 2
/* define range mapping here, -+100% -> 1000..2000 */
#define SBUS_RANGE_MIN 200.0f
#define SBUS_RANGE_MAX 1800.0f
#define SBUS_TARGET_MIN 1000.0f
#define SBUS_TARGET_MAX 2000.0f
/* pre-calculate the floating point stuff as far as possible at compile time */
#define SBUS_SCALE_FACTOR ((SBUS_TARGET_MAX - SBUS_TARGET_MIN) / (SBUS_RANGE_MAX - SBUS_RANGE_MIN))
#define SBUS_SCALE_OFFSET (int)(SBUS_TARGET_MIN - (SBUS_SCALE_FACTOR * SBUS_RANGE_MIN + 0.5f))
/*
* S.bus decoder matrix.
*
* Each channel value can come from up to 3 input bytes. Each row in the
* matrix describes up to three bytes, and each entry gives:
*
* - byte offset in the data portion of the frame
* - right shift applied to the data byte
* - mask for the data byte
* - left shift applied to the result into the channel value
*/
struct sbus_bit_pick {
uint8_t byte;
uint8_t rshift;
uint8_t mask;
uint8_t lshift;
};
static const struct sbus_bit_pick sbus_decoder[SBUS_INPUT_CHANNELS][3] = {
/* 0 */ { { 0, 0, 0xff, 0}, { 1, 0, 0x07, 8}, { 0, 0, 0x00, 0} },
/* 1 */ { { 1, 3, 0x1f, 0}, { 2, 0, 0x3f, 5}, { 0, 0, 0x00, 0} },
/* 2 */ { { 2, 6, 0x03, 0}, { 3, 0, 0xff, 2}, { 4, 0, 0x01, 10} },
/* 3 */ { { 4, 1, 0x7f, 0}, { 5, 0, 0x0f, 7}, { 0, 0, 0x00, 0} },
/* 4 */ { { 5, 4, 0x0f, 0}, { 6, 0, 0x7f, 4}, { 0, 0, 0x00, 0} },
/* 5 */ { { 6, 7, 0x01, 0}, { 7, 0, 0xff, 1}, { 8, 0, 0x03, 9} },
/* 6 */ { { 8, 2, 0x3f, 0}, { 9, 0, 0x1f, 6}, { 0, 0, 0x00, 0} },
/* 7 */ { { 9, 5, 0x07, 0}, {10, 0, 0xff, 3}, { 0, 0, 0x00, 0} },
/* 8 */ { {11, 0, 0xff, 0}, {12, 0, 0x07, 8}, { 0, 0, 0x00, 0} },
/* 9 */ { {12, 3, 0x1f, 0}, {13, 0, 0x3f, 5}, { 0, 0, 0x00, 0} },
/* 10 */ { {13, 6, 0x03, 0}, {14, 0, 0xff, 2}, {15, 0, 0x01, 10} },
/* 11 */ { {15, 1, 0x7f, 0}, {16, 0, 0x0f, 7}, { 0, 0, 0x00, 0} },
/* 12 */ { {16, 4, 0x0f, 0}, {17, 0, 0x7f, 4}, { 0, 0, 0x00, 0} },
/* 13 */ { {17, 7, 0x01, 0}, {18, 0, 0xff, 1}, {19, 0, 0x03, 9} },
/* 14 */ { {19, 2, 0x3f, 0}, {20, 0, 0x1f, 6}, { 0, 0, 0x00, 0} },
/* 15 */ { {20, 5, 0x07, 0}, {21, 0, 0xff, 3}, { 0, 0, 0x00, 0} }
};
// constructor
AP_RCProtocol_SBUS::AP_RCProtocol_SBUS(AP_RCProtocol &_frontend, bool _inverted) :
AP_RCProtocol_Backend(_frontend),
inverted(_inverted)
{}
// decode a full SBUS frame
bool AP_RCProtocol_SBUS::sbus_decode(const uint8_t frame[25], uint16_t *values, uint16_t *num_values,
bool *sbus_failsafe, bool *sbus_frame_drop, uint16_t max_values)
{
/* check frame boundary markers to avoid out-of-sync cases */
if ((frame[0] != 0x0f)) {
return false;
}
switch (frame[24]) {
case 0x00:
/* this is S.BUS 1 */
break;
case 0x03:
/* S.BUS 2 SLOT0: RX battery and external voltage */
break;
case 0x83:
/* S.BUS 2 SLOT1 */
break;
case 0x43:
case 0xC3:
case 0x23:
case 0xA3:
case 0x63:
case 0xE3:
break;
default:
/* we expect one of the bits above, but there are some we don't know yet */
break;
}
unsigned chancount = (max_values > SBUS_INPUT_CHANNELS) ?
SBUS_INPUT_CHANNELS : max_values;
/* use the decoder matrix to extract channel data */
for (unsigned channel = 0; channel < chancount; channel++) {
unsigned value = 0;
for (unsigned pick = 0; pick < 3; pick++) {
const struct sbus_bit_pick *decode = &sbus_decoder[channel][pick];
if (decode->mask != 0) {
unsigned piece = frame[1 + decode->byte];
piece >>= decode->rshift;
piece &= decode->mask;
piece <<= decode->lshift;
value |= piece;
}
}
/* convert 0-2048 values to 1000-2000 ppm encoding in a not too sloppy fashion */
values[channel] = (uint16_t)(value * SBUS_SCALE_FACTOR +.5f) + SBUS_SCALE_OFFSET;
}
/* decode switch channels if data fields are wide enough */
if (max_values > 17 && chancount > 15) {
chancount = 18;
/* channel 17 (index 16) */
values[16] = (frame[SBUS_FLAGS_BYTE] & (1 << 0))?1998:998;
/* channel 18 (index 17) */
values[17] = (frame[SBUS_FLAGS_BYTE] & (1 << 1))?1998:998;
}
/* note the number of channels decoded */
*num_values = chancount;
/* decode and handle failsafe and frame-lost flags */
if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FAILSAFE_BIT)) { /* failsafe */
/* report that we failed to read anything valid off the receiver */
*sbus_failsafe = true;
*sbus_frame_drop = true;
} else if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FRAMELOST_BIT)) { /* a frame was lost */
/* set a special warning flag
*
* Attention! This flag indicates a skipped frame only, not a total link loss! Handling this
* condition as fail-safe greatly reduces the reliability and range of the radio link,
* e.g. by prematurely issuing return-to-launch!!! */
*sbus_failsafe = false;
*sbus_frame_drop = true;
} else {
*sbus_failsafe = false;
*sbus_frame_drop = false;
}
return true;
}
/*
process a SBUS input pulse of the given width
*/
void AP_RCProtocol_SBUS::process_pulse(uint32_t width_s0, uint32_t width_s1)
{
uint32_t w0 = width_s0;
uint32_t w1 = width_s1;
if (inverted) {
w0 = saved_width;
w1 = width_s0;
saved_width = width_s1;
}
uint8_t b;
if (ss.process_pulse(w0, w1, b)) {
_process_byte(ss.get_byte_timestamp_us(), b);
}
}
// support byte input
void AP_RCProtocol_SBUS::_process_byte(uint32_t timestamp_us, uint8_t b)
{
const bool have_frame_gap = (timestamp_us - byte_input.last_byte_us >= 2000U);
byte_input.last_byte_us = timestamp_us;
if (have_frame_gap) {
// if we have a frame gap then this must be the start of a new
// frame
byte_input.ofs = 0;
}
if (b != 0x0F && byte_input.ofs == 0) {
// definately not SBUS, missing header byte
return;
}
if (byte_input.ofs == 0 && !have_frame_gap) {
// must have a frame gap before the start of a new SBUS frame
return;
}
byte_input.buf[byte_input.ofs++] = b;
if (byte_input.ofs == sizeof(byte_input.buf)) {
uint16_t values[SBUS_INPUT_CHANNELS];
uint16_t num_values=0;
bool sbus_failsafe = false;
bool sbus_frame_drop = false;
if (sbus_decode(byte_input.buf, values, &num_values,
&sbus_failsafe, &sbus_frame_drop, SBUS_INPUT_CHANNELS) &&
num_values >= MIN_RCIN_CHANNELS) {
add_input(num_values, values, sbus_failsafe);
}
byte_input.ofs = 0;
}
}
// support byte input
void AP_RCProtocol_SBUS::process_byte(uint8_t b, uint32_t baudrate)
{
if (baudrate != 100000) {
return;
}
_process_byte(AP_HAL::micros(), b);
}
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