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 FILE_COMPILE_FOR_SPEED
  25
  26 #ifdef USE_SERIAL_RX
  27
  28 #include "build/debug.h"
  29
  30 #include "common/utils.h"
  31
  32 #include "drivers/time.h"
  33
  34 #include "io/serial.h"
  35
  36 #ifdef USE_TELEMETRY
  37 #include "telemetry/telemetry.h"
  38 #endif
  39
  40 #include "rx/rx.h"
  41 #include "rx/sbus.h"
  42 #include "rx/sbus_channels.h"
  43
  44 /*
  45  * Observations
  46  *
  47  * FrSky X8R
  48  * time between frames: 6ms.
  49  * time to send frame: 3ms.
  50 *
  51  * Futaba R6208SB/R6303SB
  52  * time between frames: 11ms.
  53  * time to send frame: 3ms.
  54  */
  55 typedef enum {
  56     STATE_SBUS_SYNC = 0,
  57     STATE_SBUS_PAYLOAD,
  58     STATE_SBUS_WAIT_SYNC
  59 } sbusDecoderState_e;
  60
  61 typedef struct sbusFrameData_s {
  62     sbusDecoderState_e state;
  63     volatile sbusFrame_t frame;
  64     volatile bool frameDone;
  65     uint8_t buffer[SBUS_FRAME_SIZE];
  66     uint8_t position;
  67     timeUs_t lastActivityTimeUs;
  68 } sbusFrameData_t;
  69
  70 // Receive ISR callback
  71 static void sbusDataReceive(uint16_t c, void *data)
  72 {
  73     static uint16_t sbusDesyncCounter = 0;
  74
  75     sbusFrameData_t *sbusFrameData = data;
  76     const timeUs_t currentTimeUs = micros();
  77     const timeDelta_t timeSinceLastByteUs = cmpTimeUs(currentTimeUs, sbusFrameData->lastActivityTimeUs);
  78     sbusFrameData->lastActivityTimeUs = currentTimeUs;
  79
  80     // 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
  81     if (sbusFrameData->state == STATE_SBUS_WAIT_SYNC && timeSinceLastByteUs >= rxConfig()->sbusSyncInterval) {
  82         sbusFrameData->state = STATE_SBUS_SYNC;
  83     }
  84
  85     switch (sbusFrameData->state) {
  86         case STATE_SBUS_SYNC:
  87             if (c == SBUS_FRAME_BEGIN_BYTE) {
  88                 sbusFrameData->position = 0;
  89                 sbusFrameData->buffer[sbusFrameData->position++] = (uint8_t)c;
  90                 sbusFrameData->state = STATE_SBUS_PAYLOAD;
  91             }
  92             break;
  93
  94         case STATE_SBUS_PAYLOAD:
  95             sbusFrameData->buffer[sbusFrameData->position++] = (uint8_t)c;
  96
  97             if (sbusFrameData->position == SBUS_FRAME_SIZE) {
  98                 const sbusFrame_t * frame = (sbusFrame_t *)&sbusFrameData->buffer[0];
  99                 bool frameValid = false;
 100
 101                 // Do some sanity check
 102                 switch (frame->endByte) {
 103                     case 0x00:  // This is S.BUS 1
 104                     case 0x04:  // S.BUS 2 receiver voltage
 105                     case 0x14:  // S.BUS 2 GPS/baro
 106                     case 0x24:  // Unknown SBUS2 data
 107                     case 0x34:  // Unknown SBUS2 data
 108                         frameValid = true;
 109                         sbusFrameData->state = STATE_SBUS_WAIT_SYNC;
 110                         break;
 111
 112                     default:    // Failed end marker
 113                         sbusFrameData->state = STATE_SBUS_WAIT_SYNC;
 114                         sbusDesyncCounter++;
 115                         break;
 116                 }
 117
 118                 // Frame seems sane, pass data to decoder
 119                 if (!sbusFrameData->frameDone && frameValid) {
 120
 121                     memcpy((void *)&sbusFrameData->frame, (void *)&sbusFrameData->buffer[0], SBUS_FRAME_SIZE);
 122                     sbusFrameData->frameDone = true;
 123                 }
 124             }
 125             break;
 126
 127         case STATE_SBUS_WAIT_SYNC:
 128             // Stay at this state and do nothing. Exit will be handled before byte is processed if the
 129             // inter-frame gap is long enough
 130             break;
 131     }
 132 }
 133
 134 static uint8_t sbusFrameStatus(rxRuntimeConfig_t *rxRuntimeConfig)
 135 {
 136     sbusFrameData_t *sbusFrameData = rxRuntimeConfig->frameData;
 137
 138     if (!sbusFrameData->frameDone) {
 139         return RX_FRAME_PENDING;
 140     }
 141
 142     // Decode channel data and store return value
 143     const uint8_t retValue = sbusChannelsDecode(rxRuntimeConfig, (void *)&sbusFrameData->frame.channels);
 144
 145     // Reset the frameDone flag - tell ISR that we're ready to receive next frame
 146     sbusFrameData->frameDone = false;
 147
 148     // Calculate "virtual link quality based on packet loss metric"
 149     if (retValue & RX_FRAME_COMPLETE) {
 150         lqTrackerAccumulate(rxRuntimeConfig->lqTracker, ((retValue & RX_FRAME_DROPPED) || (retValue & RX_FRAME_FAILSAFE)) ? 0 : RSSI_MAX_VALUE);
 151     }
 152
 153     return retValue;
 154 }
 155
 156 static bool sbusInitEx(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig, uint32_t sbusBaudRate)
 157 {
 158     static uint16_t sbusChannelData[SBUS_MAX_CHANNEL];
 159     static sbusFrameData_t sbusFrameData;
 160
 161     rxRuntimeConfig->channelData = sbusChannelData;
 162     rxRuntimeConfig->frameData = &sbusFrameData;
 163
 164     sbusChannelsInit(rxRuntimeConfig);
 165
 166     rxRuntimeConfig->channelCount = SBUS_MAX_CHANNEL;
 167
 168     rxRuntimeConfig->rcFrameStatusFn = sbusFrameStatus;
 169
 170     const serialPortConfig_t *portConfig = findSerialPortConfig(FUNCTION_RX_SERIAL);
 171     if (!portConfig) {
 172         return false;
 173     }
 174
 175 #ifdef USE_TELEMETRY
 176     bool portShared = telemetryCheckRxPortShared(portConfig);
 177 #else
 178     bool portShared = false;
 179 #endif
 180
 181     serialPort_t *sBusPort = openSerialPort(portConfig->identifier,
 182         FUNCTION_RX_SERIAL,
 183         sbusDataReceive,
 184         &sbusFrameData,
 185         sbusBaudRate,
 186         portShared ? MODE_RXTX : MODE_RX,
 187         SBUS_PORT_OPTIONS |
 188             (rxConfig->serialrx_inverted ? 0 : SERIAL_INVERTED) |
 189             (tristateWithDefaultOffIsActive(rxConfig->halfDuplex) ? SERIAL_BIDIR : 0)
 190         );
 191
 192 #ifdef USE_TELEMETRY
 193     if (portShared) {
 194         telemetrySharedPort = sBusPort;
 195     }
 196 #endif
 197
 198     return sBusPort != NULL;
 199 }
 200
 201 bool sbusInit(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig)
 202 {
 203     return sbusInitEx(rxConfig, rxRuntimeConfig, SBUS_BAUDRATE);
 204 }
 205
 206 bool sbusInitFast(const rxConfig_t *rxConfig, rxRuntimeConfig_t *rxRuntimeConfig)
 207 {
 208     return sbusInitEx(rxConfig, rxRuntimeConfig, SBUS_BAUDRATE_FAST);
 209 }
 210 #endif