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author | Lorenz Meier <lm@inf.ethz.ch> | 2013-04-28 01:17:12 +0200 |
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committer | Lorenz Meier <lm@inf.ethz.ch> | 2013-04-28 01:30:14 +0200 |
commit | f57439b90e23de260259dec051d3e2ead2d61c8c (patch) | |
tree | 5cd778d2cf0c9afb2851ab9042bbecc5b742a497 /src/modules/px4iofirmware/sbus.c | |
parent | 8040b9b96e8f7c07aa981150c33f850096062f70 (diff) | |
download | px4-firmware-f57439b90e23de260259dec051d3e2ead2d61c8c.tar.gz px4-firmware-f57439b90e23de260259dec051d3e2ead2d61c8c.tar.bz2 px4-firmware-f57439b90e23de260259dec051d3e2ead2d61c8c.zip |
Moved all drivers to new world, PX4IO completely in new world
Diffstat (limited to 'src/modules/px4iofirmware/sbus.c')
-rw-r--r-- | src/modules/px4iofirmware/sbus.c | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/src/modules/px4iofirmware/sbus.c b/src/modules/px4iofirmware/sbus.c new file mode 100644 index 000000000..073ddeaba --- /dev/null +++ b/src/modules/px4iofirmware/sbus.c @@ -0,0 +1,255 @@ +/**************************************************************************** + * + * Copyright (C) 2012 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. + * + ****************************************************************************/ + +/** + * @file sbus.c + * + * Serial protocol decoder for the Futaba S.bus protocol. + */ + +#include <nuttx/config.h> + +#include <fcntl.h> +#include <unistd.h> +#include <termios.h> + +#include <systemlib/ppm_decode.h> + +#include <drivers/drv_hrt.h> + +#define DEBUG +#include "px4io.h" +#include "protocol.h" +#include "debug.h" + +#define SBUS_FRAME_SIZE 25 +#define SBUS_INPUT_CHANNELS 16 + +static int sbus_fd = -1; + +static hrt_abstime last_rx_time; +static hrt_abstime last_frame_time; + +static uint8_t frame[SBUS_FRAME_SIZE]; + +static unsigned partial_frame_count; + +unsigned sbus_frame_drops; + +static bool sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values); + +int +sbus_init(const char *device) +{ + if (sbus_fd < 0) + sbus_fd = open(device, O_RDONLY | O_NONBLOCK); + + if (sbus_fd >= 0) { + struct termios t; + + /* 100000bps, even parity, two stop bits */ + tcgetattr(sbus_fd, &t); + cfsetspeed(&t, 100000); + t.c_cflag |= (CSTOPB | PARENB); + tcsetattr(sbus_fd, TCSANOW, &t); + + /* initialise the decoder */ + partial_frame_count = 0; + last_rx_time = hrt_absolute_time(); + + debug("S.Bus: ready"); + + } else { + debug("S.Bus: open failed"); + } + + return sbus_fd; +} + +bool +sbus_input(uint16_t *values, uint16_t *num_values) +{ + ssize_t ret; + hrt_abstime now; + + /* + * The S.bus protocol doesn't provide reliable framing, + * so we detect frame boundaries by the inter-frame delay. + * + * The minimum frame spacing is 7ms; with 25 bytes at 100000bps + * frame transmission time is ~2ms. + * + * We expect to only be called when bytes arrive for processing, + * and if an interval of more than 3ms passes between calls, + * the first byte we read will be the first byte of a frame. + * + * In the case where byte(s) are dropped from a frame, this also + * provides a degree of protection. Of course, it would be better + * if we didn't drop bytes... + */ + now = hrt_absolute_time(); + + if ((now - last_rx_time) > 3000) { + if (partial_frame_count > 0) { + sbus_frame_drops++; + partial_frame_count = 0; + } + } + + /* + * Fetch bytes, but no more than we would need to complete + * the current frame. + */ + ret = read(sbus_fd, &frame[partial_frame_count], SBUS_FRAME_SIZE - partial_frame_count); + + /* if the read failed for any reason, just give up here */ + if (ret < 1) + return false; + + last_rx_time = now; + + /* + * Add bytes to the current frame + */ + partial_frame_count += ret; + + /* + * If we don't have a full frame, return + */ + if (partial_frame_count < SBUS_FRAME_SIZE) + return false; + + /* + * Great, it looks like we might have a frame. Go ahead and + * decode it. + */ + partial_frame_count = 0; + return sbus_decode(now, values, num_values); +} + +/* + * 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} } +}; + +static bool +sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values) +{ + /* check frame boundary markers to avoid out-of-sync cases */ + if ((frame[0] != 0x0f) || (frame[24] != 0x00)) { + sbus_frame_drops++; + return false; + } + + /* if the failsafe or connection lost bit is set, we consider the frame invalid */ + if ((frame[23] & (1 << 2)) && /* signal lost */ + (frame[23] & (1 << 3))) { /* failsafe */ + + /* actively announce signal loss */ + *values = 0; + return false; + } + + /* we have received something we think is a frame */ + last_frame_time = frame_time; + + unsigned chancount = (PX4IO_INPUT_CHANNELS > SBUS_INPUT_CHANNELS) ? + SBUS_INPUT_CHANNELS : PX4IO_INPUT_CHANNELS; + + /* 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 very sloppy fashion */ + values[channel] = (value / 2) + 998; + } + + /* decode switch channels if data fields are wide enough */ + if (PX4IO_INPUT_CHANNELS > 17 && chancount > 15) { + chancount = 18; + + /* channel 17 (index 16) */ + values[16] = (frame[23] & (1 << 0)) * 1000 + 998; + /* channel 18 (index 17) */ + values[17] = (frame[23] & (1 << 1)) * 1000 + 998; + } + + /* note the number of channels decoded */ + *num_values = chancount; + + return true; +} |