forked from Archive/PX4-Autopilot
256 lines
7.5 KiB
C
256 lines
7.5 KiB
C
/****************************************************************************
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*
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* Copyright (C) 2012 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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/**
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* @file sbus.c
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*
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* Serial protocol decoder for the Futaba S.bus protocol.
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*/
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#include <nuttx/config.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <termios.h>
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#include <systemlib/ppm_decode.h>
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#include <drivers/drv_hrt.h>
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#define DEBUG
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#include "px4io.h"
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#include "protocol.h"
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#include "debug.h"
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#define SBUS_FRAME_SIZE 25
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#define SBUS_INPUT_CHANNELS 16
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static int sbus_fd = -1;
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static hrt_abstime last_rx_time;
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static hrt_abstime last_frame_time;
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static uint8_t frame[SBUS_FRAME_SIZE];
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static unsigned partial_frame_count;
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unsigned sbus_frame_drops;
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static bool sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values);
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int
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sbus_init(const char *device)
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{
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if (sbus_fd < 0)
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sbus_fd = open(device, O_RDONLY | O_NONBLOCK);
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if (sbus_fd >= 0) {
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struct termios t;
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/* 100000bps, even parity, two stop bits */
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tcgetattr(sbus_fd, &t);
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cfsetspeed(&t, 100000);
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t.c_cflag |= (CSTOPB | PARENB);
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tcsetattr(sbus_fd, TCSANOW, &t);
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/* initialise the decoder */
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partial_frame_count = 0;
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last_rx_time = hrt_absolute_time();
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debug("S.Bus: ready");
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} else {
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debug("S.Bus: open failed");
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}
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return sbus_fd;
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}
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bool
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sbus_input(uint16_t *values, uint16_t *num_values)
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{
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ssize_t ret;
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hrt_abstime now;
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/*
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* The S.bus protocol doesn't provide reliable framing,
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* so we detect frame boundaries by the inter-frame delay.
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*
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* The minimum frame spacing is 7ms; with 25 bytes at 100000bps
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* frame transmission time is ~2ms.
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*
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* We expect to only be called when bytes arrive for processing,
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* and if an interval of more than 3ms passes between calls,
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* the first byte we read will be the first byte of a frame.
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*
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* In the case where byte(s) are dropped from a frame, this also
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* provides a degree of protection. Of course, it would be better
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* if we didn't drop bytes...
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*/
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now = hrt_absolute_time();
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if ((now - last_rx_time) > 3000) {
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if (partial_frame_count > 0) {
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sbus_frame_drops++;
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partial_frame_count = 0;
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}
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}
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/*
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* Fetch bytes, but no more than we would need to complete
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* the current frame.
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*/
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ret = read(sbus_fd, &frame[partial_frame_count], SBUS_FRAME_SIZE - partial_frame_count);
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/* if the read failed for any reason, just give up here */
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if (ret < 1)
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return false;
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last_rx_time = now;
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/*
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* Add bytes to the current frame
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*/
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partial_frame_count += ret;
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/*
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* If we don't have a full frame, return
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*/
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if (partial_frame_count < SBUS_FRAME_SIZE)
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return false;
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/*
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* Great, it looks like we might have a frame. Go ahead and
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* decode it.
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*/
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partial_frame_count = 0;
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return sbus_decode(now, values, num_values);
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}
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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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static bool
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sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_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) || (frame[24] != 0x00)) {
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sbus_frame_drops++;
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return false;
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}
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/* if the failsafe or connection lost bit is set, we consider the frame invalid */
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if ((frame[23] & (1 << 2)) && /* signal lost */
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(frame[23] & (1 << 3))) { /* failsafe */
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/* actively announce signal loss */
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*values = 0;
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return false;
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}
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/* we have received something we think is a frame */
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last_frame_time = frame_time;
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unsigned chancount = (PX4IO_INPUT_CHANNELS > SBUS_INPUT_CHANNELS) ?
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SBUS_INPUT_CHANNELS : PX4IO_INPUT_CHANNELS;
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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 very sloppy fashion */
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values[channel] = (value / 2) + 998;
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}
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/* decode switch channels if data fields are wide enough */
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if (PX4IO_INPUT_CHANNELS > 17 && chancount > 15) {
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chancount = 18;
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/* channel 17 (index 16) */
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values[16] = (frame[23] & (1 << 0)) * 1000 + 998;
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/* channel 18 (index 17) */
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values[17] = (frame[23] & (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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return true;
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}
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