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-rw-r--r--src/lib/rc/st24.c253
1 files changed, 253 insertions, 0 deletions
diff --git a/src/lib/rc/st24.c b/src/lib/rc/st24.c
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+++ b/src/lib/rc/st24.c
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+/****************************************************************************
+ *
+ * Copyright (c) 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.
+ *
+ ****************************************************************************/
+
+/*
+ * @file st24.h
+ *
+ * RC protocol implementation for Yuneec ST24 transmitter.
+ *
+ * @author Lorenz Meier <lm@inf.ethz.ch>
+ */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include "st24.h"
+
+enum ST24_DECODE_STATE {
+ ST24_DECODE_STATE_UNSYNCED = 0,
+ ST24_DECODE_STATE_GOT_STX1,
+ ST24_DECODE_STATE_GOT_STX2,
+ ST24_DECODE_STATE_GOT_LEN,
+ ST24_DECODE_STATE_GOT_TYPE,
+ ST24_DECODE_STATE_GOT_DATA
+};
+
+const char *decode_states[] = {"UNSYNCED",
+ "GOT_STX1",
+ "GOT_STX2",
+ "GOT_LEN",
+ "GOT_TYPE",
+ "GOT_DATA"
+ };
+
+/* define range mapping here, -+100% -> 1000..2000 */
+#define ST24_RANGE_MIN 0.0f
+#define ST24_RANGE_MAX 4096.0f
+
+#define ST24_TARGET_MIN 1000.0f
+#define ST24_TARGET_MAX 2000.0f
+
+/* pre-calculate the floating point stuff as far as possible at compile time */
+#define ST24_SCALE_FACTOR ((ST24_TARGET_MAX - ST24_TARGET_MIN) / (ST24_RANGE_MAX - ST24_RANGE_MIN))
+#define ST24_SCALE_OFFSET (int)(ST24_TARGET_MIN - (ST24_SCALE_FACTOR * ST24_RANGE_MIN + 0.5f))
+
+static enum ST24_DECODE_STATE _decode_state = ST24_DECODE_STATE_UNSYNCED;
+static unsigned _rxlen;
+
+static ReceiverFcPacket _rxpacket;
+
+uint8_t st24_common_crc8(uint8_t *ptr, uint8_t len)
+{
+ uint8_t i, crc ;
+ crc = 0;
+
+ while (len--) {
+ for (i = 0x80; i != 0; i >>= 1) {
+ if ((crc & 0x80) != 0) {
+ crc <<= 1;
+ crc ^= 0x07;
+
+ } else {
+ crc <<= 1;
+ }
+
+ if ((*ptr & i) != 0) {
+ crc ^= 0x07;
+ }
+ }
+
+ ptr++;
+ }
+
+ return (crc);
+}
+
+
+int st24_decode(uint8_t byte, uint8_t *rssi, uint8_t *rx_count, uint16_t *channel_count, uint16_t *channels,
+ uint16_t max_chan_count)
+{
+
+ int ret = 1;
+
+ switch (_decode_state) {
+ case ST24_DECODE_STATE_UNSYNCED:
+ if (byte == ST24_STX1) {
+ _decode_state = ST24_DECODE_STATE_GOT_STX1;
+ } else {
+ ret = 3;
+ }
+
+ break;
+
+ case ST24_DECODE_STATE_GOT_STX1:
+ if (byte == ST24_STX2) {
+ _decode_state = ST24_DECODE_STATE_GOT_STX2;
+
+ } else {
+ _decode_state = ST24_DECODE_STATE_UNSYNCED;
+ }
+
+ break;
+
+ case ST24_DECODE_STATE_GOT_STX2:
+
+ /* ensure no data overflow failure or hack is possible */
+ if ((unsigned)byte <= sizeof(_rxpacket.length) + sizeof(_rxpacket.type) + sizeof(_rxpacket.st24_data)) {
+ _rxpacket.length = byte;
+ _rxlen = 0;
+ _decode_state = ST24_DECODE_STATE_GOT_LEN;
+
+ } else {
+ _decode_state = ST24_DECODE_STATE_UNSYNCED;
+ }
+
+ break;
+
+ case ST24_DECODE_STATE_GOT_LEN:
+ _rxpacket.type = byte;
+ _rxlen++;
+ _decode_state = ST24_DECODE_STATE_GOT_TYPE;
+ break;
+
+ case ST24_DECODE_STATE_GOT_TYPE:
+ _rxpacket.st24_data[_rxlen - 1] = byte;
+ _rxlen++;
+
+ if (_rxlen == (_rxpacket.length - 1)) {
+ _decode_state = ST24_DECODE_STATE_GOT_DATA;
+ }
+
+ break;
+
+ case ST24_DECODE_STATE_GOT_DATA:
+ _rxpacket.crc8 = byte;
+ _rxlen++;
+
+ if (st24_common_crc8((uint8_t *) & (_rxpacket.length), _rxlen) == _rxpacket.crc8) {
+
+ ret = 0;
+
+ /* decode the actual packet */
+
+ switch (_rxpacket.type) {
+
+ case ST24_PACKET_TYPE_CHANNELDATA12: {
+ ChannelData12 *d = (ChannelData12 *)_rxpacket.st24_data;
+
+ *rssi = d->rssi;
+ *rx_count = d->packet_count;
+
+ /* this can lead to rounding of the strides */
+ *channel_count = (max_chan_count < 12) ? max_chan_count : 12;
+
+ unsigned stride_count = (*channel_count * 3) / 2;
+ unsigned chan_index = 0;
+
+ for (unsigned i = 0; i < stride_count; i += 3) {
+ channels[chan_index] = ((uint16_t)d->channel[i] << 4);
+ channels[chan_index] |= ((uint16_t)(0xF0 & d->channel[i + 1]) >> 4);
+ /* convert values to 1000-2000 ppm encoding in a not too sloppy fashion */
+ channels[chan_index] = (uint16_t)(channels[chan_index] * ST24_SCALE_FACTOR + .5f) + ST24_SCALE_OFFSET;
+ chan_index++;
+
+ channels[chan_index] = ((uint16_t)d->channel[i + 2]);
+ channels[chan_index] |= (((uint16_t)(0x0F & d->channel[i + 1])) << 8);
+ /* convert values to 1000-2000 ppm encoding in a not too sloppy fashion */
+ channels[chan_index] = (uint16_t)(channels[chan_index] * ST24_SCALE_FACTOR + .5f) + ST24_SCALE_OFFSET;
+ chan_index++;
+ }
+ }
+ break;
+
+ case ST24_PACKET_TYPE_CHANNELDATA24: {
+ ChannelData24 *d = (ChannelData24 *)&_rxpacket.st24_data;
+
+ *rssi = d->rssi;
+ *rx_count = d->packet_count;
+
+ /* this can lead to rounding of the strides */
+ *channel_count = (max_chan_count < 24) ? max_chan_count : 24;
+
+ unsigned stride_count = (*channel_count * 3) / 2;
+ unsigned chan_index = 0;
+
+ for (unsigned i = 0; i < stride_count; i += 3) {
+ channels[chan_index] = ((uint16_t)d->channel[i] << 4);
+ channels[chan_index] |= ((uint16_t)(0xF0 & d->channel[i + 1]) >> 4);
+ /* convert values to 1000-2000 ppm encoding in a not too sloppy fashion */
+ channels[chan_index] = (uint16_t)(channels[chan_index] * ST24_SCALE_FACTOR + .5f) + ST24_SCALE_OFFSET;
+ chan_index++;
+
+ channels[chan_index] = ((uint16_t)d->channel[i + 2]);
+ channels[chan_index] |= (((uint16_t)(0x0F & d->channel[i + 1])) << 8);
+ /* convert values to 1000-2000 ppm encoding in a not too sloppy fashion */
+ channels[chan_index] = (uint16_t)(channels[chan_index] * ST24_SCALE_FACTOR + .5f) + ST24_SCALE_OFFSET;
+ chan_index++;
+ }
+ }
+ break;
+
+ case ST24_PACKET_TYPE_TRANSMITTERGPSDATA: {
+
+ // ReceiverFcPacket* d = (ReceiverFcPacket*)&_rxpacket.st24_data;
+ /* we silently ignore this data for now, as it is unused */
+ ret = 2;
+ }
+ break;
+
+ default:
+ ret = 2;
+ break;
+ }
+
+ } else {
+ /* decoding failed */
+ ret = 4;
+ }
+
+ _decode_state = ST24_DECODE_STATE_UNSYNCED;
+ break;
+ }
+
+ return ret;
+}
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