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HAL_Linux: added low level DSM decoder
based on dsm.c from PX4 project
This commit is contained in:
Andrew Tridgell
parent
adf741b959
commit
50e5ae6f7a
309
libraries/AP_HAL_Linux/dsm.cpp
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309
libraries/AP_HAL_Linux/dsm.cpp
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// -*- tab-width: 8; Mode: C++; c-basic-offset: 8; indent-tabs-mode: -*- t -*-
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/*
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DSM decoder, based on src/modules/px4iofirmware/dsm.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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#define DSM_FRAME_SIZE 16 /**<DSM frame size in bytes*/
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#define DSM_FRAME_CHANNELS 7 /**<Max supported DSM channels*/
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static uint64_t dsm_last_frame_time; /**< Timestamp for start of last dsm frame */
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static unsigned dsm_channel_shift; /**< Channel resolution, 0=unknown, 1=10 bit, 2=11 bit */
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#ifdef DEBUG
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# define debug(fmt, args...) printf(fmt "\n", ##args)
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#else
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# define debug(fmt, args...) do {} while(0)
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#endif
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/**
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* Attempt to decode a single channel raw channel datum
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*
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* The DSM* protocol doesn't provide any explicit framing,
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* so we detect dsm frame boundaries by the inter-dsm frame delay.
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*
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* The minimum dsm frame spacing is 11ms; with 16 bytes at 115200bps
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* dsm frame transmission time is ~1.4ms.
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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 5ms passes between calls,
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* the first byte we read will be the first byte of a dsm frame.
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*
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* In the case where byte(s) are dropped from a dsm 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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* Upon receiving a full dsm frame we attempt to decode it
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*
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* @param[in] raw 16 bit raw channel value from dsm frame
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* @param[in] shift position of channel number in raw data
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* @param[out] channel pointer to returned channel number
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* @param[out] value pointer to returned channel value
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* @return true=raw value successfully decoded
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*/
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static bool
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dsm_decode_channel(uint16_t raw, unsigned shift, unsigned *channel, unsigned *value)
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{
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if (raw == 0xffff)
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return false;
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*channel = (raw >> shift) & 0xf;
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uint16_t data_mask = (1 << shift) - 1;
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*value = raw & data_mask;
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//debug("DSM: %d 0x%04x -> %d %d", shift, raw, *channel, *value);
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return true;
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}
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/**
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* Attempt to guess if receiving 10 or 11 bit channel values
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*
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* @param[in] reset true=reset the 10/11 bit state to unknown
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*/
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static void
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dsm_guess_format(bool reset, const uint8_t dsm_frame[16])
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{
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static uint32_t cs10;
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static uint32_t cs11;
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static unsigned samples;
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/* reset the 10/11 bit sniffed channel masks */
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if (reset) {
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cs10 = 0;
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cs11 = 0;
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samples = 0;
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dsm_channel_shift = 0;
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return;
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}
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/* scan the channels in the current dsm_frame in both 10- and 11-bit mode */
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for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
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const uint8_t *dp = &dsm_frame[2 + (2 * i)];
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uint16_t raw = (dp[0] << 8) | dp[1];
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unsigned channel, value;
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/* if the channel decodes, remember the assigned number */
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if (dsm_decode_channel(raw, 10, &channel, &value) && (channel < 31))
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cs10 |= (1 << channel);
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if (dsm_decode_channel(raw, 11, &channel, &value) && (channel < 31))
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cs11 |= (1 << channel);
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/* XXX if we cared, we could look for the phase bit here to decide 1 vs. 2-dsm_frame format */
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}
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/* wait until we have seen plenty of frames - 5 should normally be enough */
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if (samples++ < 5)
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return;
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/*
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* Iterate the set of sensible sniffed channel sets and see whether
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* decoding in 10 or 11-bit mode has yielded anything we recognize.
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*
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* XXX Note that due to what seem to be bugs in the DSM2 high-resolution
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* stream, we may want to sniff for longer in some cases when we think we
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* are talking to a DSM2 receiver in high-resolution mode (so that we can
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* reject it, ideally).
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* See e.g. http://git.openpilot.org/cru/OPReview-116 for a discussion
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* of this issue.
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*/
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static uint32_t masks[] = {
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0x3f, /* 6 channels (DX6) */
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0x7f, /* 7 channels (DX7) */
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0xff, /* 8 channels (DX8) */
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0x1ff, /* 9 channels (DX9, etc.) */
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0x3ff, /* 10 channels (DX10) */
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0x1fff, /* 13 channels (DX10t) */
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0x3fff /* 18 channels (DX10) */
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};
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unsigned votes10 = 0;
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unsigned votes11 = 0;
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for (unsigned i = 0; i < (sizeof(masks) / sizeof(masks[0])); i++) {
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if (cs10 == masks[i])
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votes10++;
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if (cs11 == masks[i])
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votes11++;
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}
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if ((votes11 == 1) && (votes10 == 0)) {
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dsm_channel_shift = 11;
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debug("DSM: 11-bit format");
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return;
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}
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if ((votes10 == 1) && (votes11 == 0)) {
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dsm_channel_shift = 10;
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debug("DSM: 10-bit format");
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return;
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}
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/* call ourselves to reset our state ... we have to try again */
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debug("DSM: format detect fail, 10: 0x%08x %d 11: 0x%08x %d", cs10, votes10, cs11, votes11);
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dsm_guess_format(true, dsm_frame);
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}
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/**
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* Decode the entire dsm frame (all contained channels)
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*
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*/
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bool
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dsm_decode(uint64_t frame_time, const uint8_t dsm_frame[16], uint16_t *values, uint16_t *num_values, uint16_t max_values)
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{
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/*
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debug("DSM dsm_frame %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x",
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dsm_frame[0], dsm_frame[1], dsm_frame[2], dsm_frame[3], dsm_frame[4], dsm_frame[5], dsm_frame[6], dsm_frame[7],
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dsm_frame[8], dsm_frame[9], dsm_frame[10], dsm_frame[11], dsm_frame[12], dsm_frame[13], dsm_frame[14], dsm_frame[15]);
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*/
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/*
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* If we have lost signal for at least a second, reset the
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* format guessing heuristic.
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*/
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if (((frame_time - dsm_last_frame_time) > 1000000) && (dsm_channel_shift != 0))
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dsm_guess_format(true, dsm_frame);
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/* we have received something we think is a dsm_frame */
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dsm_last_frame_time = frame_time;
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/* if we don't know the dsm_frame format, update the guessing state machine */
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if (dsm_channel_shift == 0) {
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dsm_guess_format(false, dsm_frame);
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return false;
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}
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/*
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* The encoding of the first two bytes is uncertain, so we're
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* going to ignore them for now.
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*
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* Each channel is a 16-bit unsigned value containing either a 10-
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* or 11-bit channel value and a 4-bit channel number, shifted
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* either 10 or 11 bits. The MSB may also be set to indicate the
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* second dsm_frame in variants of the protocol where more than
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* seven channels are being transmitted.
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*/
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for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
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const uint8_t *dp = &dsm_frame[2 + (2 * i)];
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uint16_t raw = (dp[0] << 8) | dp[1];
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unsigned channel, value;
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if (!dsm_decode_channel(raw, dsm_channel_shift, &channel, &value))
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continue;
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/* ignore channels out of range */
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if (channel >= max_values)
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continue;
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/* update the decoded channel count */
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if (channel >= *num_values)
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*num_values = channel + 1;
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/* convert 0-1024 / 0-2048 values to 1000-2000 ppm encoding. */
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if (dsm_channel_shift == 10)
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value *= 2;
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/*
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* Spektrum scaling is special. There are these basic considerations
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*
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* * Midpoint is 1520 us
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* * 100% travel channels are +- 400 us
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*
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* We obey the original Spektrum scaling (so a default setup will scale from
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* 1100 - 1900 us), but we do not obey the weird 1520 us center point
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* and instead (correctly) center the center around 1500 us. This is in order
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* to get something useful without requiring the user to calibrate on a digital
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* link for no reason.
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*/
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/* scaled integer for decent accuracy while staying efficient */
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value = ((((int)value - 1024) * 1000) / 1700) + 1500;
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/*
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* Store the decoded channel into the R/C input buffer, taking into
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* account the different ideas about channel assignement that we have.
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*
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* Specifically, the first four channels in rc_channel_data are roll, pitch, thrust, yaw,
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* but the first four channels from the DSM receiver are thrust, roll, pitch, yaw.
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*/
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switch (channel) {
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case 0:
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channel = 2;
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break;
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case 1:
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channel = 0;
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break;
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case 2:
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channel = 1;
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default:
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break;
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}
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values[channel] = value;
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}
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/*
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* Spektrum likes to send junk in higher channel numbers to fill
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* their packets. We don't know about a 13 channel model in their TX
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* lines, so if we get a channel count of 13, we'll return 12 (the last
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* data index that is stable).
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*/
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if (*num_values == 13)
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*num_values = 12;
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#if 0
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if (dsm_channel_shift == 11) {
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/* Set the 11-bit data indicator */
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*num_values |= 0x8000;
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}
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#endif
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/*
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* XXX Note that we may be in failsafe here; we need to work out how to detect that.
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*/
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return true;
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}
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8
libraries/AP_HAL_Linux/dsm.h
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8
libraries/AP_HAL_Linux/dsm.h
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@ -0,0 +1,8 @@
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/*
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declaration of dsm_decode from dsm.cpp
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*/
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bool dsm_decode(uint64_t frame_time, const uint8_t dsm_frame[16],
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uint16_t *values,
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uint16_t *num_values,
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uint16_t max_values);
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