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