src/main/rx/sbus.c

   1 /*
   2  * This file is part of Cleanflight.
   3  *
   4  * Cleanflight is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * Cleanflight is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <stdbool.h>
  19 #include <stdint.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22
  23 #include "platform.h"
  24
  25 #ifdef USE_SERIAL_RX
  26
  27 #include "build/debug.h"
  28
  29 #include "common/utils.h"
  30
  31 #include "drivers/time.h"
  32
  33 #include "io/serial.h"
  34
  35 #ifdef USE_TELEMETRY
  36 #include "telemetry/telemetry.h"
  37 #endif
  38
  39 #include "rx/rx.h"
  40 #include "rx/sbus.h"
  41 #include "rx/sbus_channels.h"
  42
  43 /*
  44  * Observations
  45  *
  46  * FrSky X8R
  47  * time between frames: 6ms.
  48  * time to send frame: 3ms.
  49 *
  50  * Futaba R6208SB/R6303SB
  51  * time between frames: 11ms.
  52  * time to send frame: 3ms.
  53  */
  54 typedef enum {
  55     STATE_SBUS_SYNC = 0,
  56     STATE_SBUS_PAYLOAD,
  57     STATE_SBUS_WAIT_SYNC
  58 } sbusDecoderState_e;
  59
  60 typedef struct sbusFrameData_s {
  61     sbusDecoderState_e state;
  62     volatile sbusFrame_t frame;
  63     volatile bool frameDone;
  64     uint8_t buffer[SBUS_FRAME_SIZE];
  65     uint8_t position;
  66     timeUs_t lastActivityTimeUs;
  67 } sbusFrameData_t;
  68
  69 // Receive ISR callback
  70 static void sbusDataReceive(uint16_t c, void *data)
  71 {
  72     sbusFrameData_t *sbusFrameData = data;
  73     const timeUs_t currentTimeUs = micros();
  74     const timeDelta_t timeSinceLastByteUs = cmpTimeUs(currentTimeUs, sbusFrameData->lastActivityTimeUs);
  75     sbusFrameData->lastActivityTimeUs = currentTimeUs;
  76
  77     // Handle inter-frame gap. We dwell in STATE_SBUS_WAIT_SYNC state ignoring all incoming bytes until we get long enough quite period on the wire
  78     if (sbusFrameData->state == STATE_SBUS_WAIT_SYNC && timeSinceLastByteUs >= rxConfig()->sbusSyncInterval) {
  79         sbusFrameData->state = STATE_SBUS_SYNC;
  80     }
  81
  82     switch (sbusFrameData->state) {
  83         case STATE_SBUS_SYNC:
  84             if (c == SBUS_FRAME_BEGIN_BYTE) {
  85                 sbusFrameData->position = 0;
  86                 sbusFrameData->buffer[sbusFrameData->position++] = (uint8_t)c;
  87                 sbusFrameData->state = STATE_SBUS_PAYLOAD;
  88             }
  89             break;
  90
  91         case STATE_SBUS_PAYLOAD:
  92             sbusFrameData->buffer[sbusFrameData->position++] = (uint8_t)c;
  93
  94             if (sbusFrameData->position == SBUS_FRAME_SIZE) {
  95                 const sbusFrame_t * frame = (sbusFrame_t *)&sbusFrameData->buffer[0];
  96                 bool frameValid = false;
  97
  98                 // Do some sanity check
  99                 switch (frame->endByte) {
 100                     case 0x00:  // This is S.BUS 1
 101                     case 0x04:  // S.BUS 2 receiver voltage
 102                     case 0x14:  // S.BUS 2 GPS/baro
 103                     case 0x24:  // Unknown SBUS2 data
 104                     case 0x34:  // Unknown SBUS2 data
 105                         frameValid = true;
 106                         sbusFrameData->state = STATE_SBUS_WAIT_SYNC;
 107                         break;
 108
 109                     default:    // Failed end marker
 110                         sbusFrameData->state = STATE_SBUS_WAIT_SYNC;
 111                         break;
 112                 }
 113
 114                 // Frame seems sane, pass data to decoder
 115                 if (!sbusFrameData->frameDone && frameValid) {
 116
 117                     memcpy((void *)&sbusFrameData->frame, (void *)&sbusFrameData->buffer[0], SBUS_FRAME_SIZE);
 118                     sbusFrameData->frameDone = true;
 119                 }
 120             }
 121             break;
 122
 123         case STATE_SBUS_WAIT_SYNC:
 124             // Stay at this state and do nothing. Exit will be handled before byte is processed if the
 125             // inter-frame gap is long enough
 126             break;
 127     }
 128 }
 129
 130 static uint8_t sbusFrameStatus(rxRuntimeConfig_t *rxRuntimeConfig)
 131 {
 132     sbusFrameData_t *sbusFrameData = rxRuntimeConfig->frameData;
 133
 134     if (!sbusFrameData->frameDone) {
 135         return RX_FRAME_PENDING;
 136     }
 137
 138     // Decode channel data and store return value
 139     const uint8_t retValue = sbusChannelsDecode(rxRuntimeConfig, (void *)&sbusFrameData->frame.channels);
 140
 141     // Reset the frameDone flag - tell ISR that we're ready to receive next frame
 142     sbusFrameData->frameDone = false;
 143
 144     // Calculate "virtual link quality based on packet loss metric"
 145     if (retValue & RX_FRAME_COMPLETE) {
 146         lqTrackerAccumulate(rxRuntimeConfig->lqTracker, ((retValue & RX_FRAME_DROPPED) || (retValue & RX_FRAME_FAILSAFE)) ? 0 : RSSI_MAX_VALUE);
 147     }
 148
 149     return retValue;
 150 }
 151
 152 static bool sbusInitEx(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig, uint32_t sbusBaudRate)
 153 {
 154     static uint16_t sbusChannelData[SBUS_MAX_CHANNEL];
 155     static sbusFrameData_t sbusFrameData;
 156
 157     rxRuntimeConfig->channelData = sbusChannelData;
 158     rxRuntimeConfig->frameData = &sbusFrameData;
 159
 160     sbusChannelsInit(rxRuntimeConfig);
 161
 162     rxRuntimeConfig->channelCount = SBUS_MAX_CHANNEL;
 163
 164     rxRuntimeConfig->rcFrameStatusFn = sbusFrameStatus;
 165
 166     const serialPortConfig_t *portConfig = findSerialPortConfig(FUNCTION_RX_SERIAL);
 167     if (!portConfig) {
 168         return false;
 169     }
 170
 171 #ifdef USE_TELEMETRY
 172     bool portShared = telemetryCheckRxPortShared(portConfig);
 173 #else
 174     bool portShared = false;
 175 #endif
 176
 177     serialPort_t *sBusPort = openSerialPort(portConfig->identifier,
 178         FUNCTION_RX_SERIAL,
 179         sbusDataReceive,
 180         &sbusFrameData,
 181         sbusBaudRate,
 182         portShared ? MODE_RXTX : MODE_RX,
 183         SBUS_PORT_OPTIONS |
 184             (rxConfig->serialrx_inverted ? 0 : SERIAL_INVERTED) |
 185             (tristateWithDefaultOffIsActive(rxConfig->halfDuplex) ? SERIAL_BIDIR : 0)
 186         );
 187
 188 #ifdef USE_TELEMETRY
 189     if (portShared) {
 190         telemetrySharedPort = sBusPort;
 191     }
 192 #endif
 193
 194     return sBusPort != NULL;
 195 }
 196
 197 bool sbusInit(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig)
 198 {
 199     return sbusInitEx(rxConfig, rxRuntimeConfig, SBUS_BAUDRATE);
 200 }
 201
 202 bool sbusInitFast(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig)
 203 {
 204     return sbusInitEx(rxConfig, rxRuntimeConfig, SBUS_BAUDRATE_FAST);
 205 }
 206 #endif