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Playing around with crsfv3 rc packets #10167

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Playing around with crsfv3 rc packets #10167

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12cb754
Basic handling of variable channel counts
mmosca Jun 21, 2024
6df7d6d
Parse variable number of channels in crossfire, with 11, 12 or 13 bits
mmosca Jun 21, 2024
a564ac4
Fix typos
mmosca Jun 21, 2024
978818b
Advance buffer
mmosca Jun 21, 2024
c43262e
Some extra checks
mmosca Jun 21, 2024
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144 changes: 144 additions & 0 deletions src/main/rx/crsf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,49 @@ struct crsfPayloadRcChannelsPacked_s {

typedef struct crsfPayloadRcChannelsPacked_s crsfPayloadRcChannelsPacked_t;

enum crsfSubsetRcResolution_e {
CRSF_11_BIT = 0,
CRSF_12_BIT = 1,
CRSF_13_BIT = 3
};

typedef struct crsfPayloadSubsetRcChannelsHeaderPacked_s { // minimum 8 channels
// 176 bits of data (11 bits per channel * 16 channels) + header = 23 bytes.
uint8_t firstChannel:5;
uint8_t resolution:2;
uint8_t reserved:1;
} __attribute__ ((__packed__)) crsfPayloadSubsetRcChannelsHeaderPacked_t;

typedef struct crsfPayloadSubsetRcChannels11Packed_s {
// 176 bits of data (12 bits per channel * 8 channels) = 11 bytes.
unsigned int chan0 : 11;
unsigned int chan1 : 11;
unsigned int chan2 : 11;
unsigned int chan3 : 11;
unsigned int chan4 : 11;
unsigned int chan5 : 11;
unsigned int chan6 : 11;
unsigned int chan7 : 11;
} crsfPayloadSubsetRcChannels11Packed_t;

typedef struct crsfPayloadSubsetRcChannels12Packed_s { // minimum 2 channels
// 176 bits of data (12 bits per channel * 8 channels) = 3 bytes.
unsigned int chan0 : 12;
unsigned int chan1 : 12;
} __attribute__ ((__packed__)) crsfPayloadSubsetRcChannels12Packed_t;

typedef struct crsfPayloadSubsetRcChannels13Packed_s { // minimum 8 channels
// 176 bits of data (13 bits per channel * 8 channels) = 13 bytes.
unsigned int chan0 : 13;
unsigned int chan1 : 13;
unsigned int chan2 : 13;
unsigned int chan3 : 13;
unsigned int chan4 : 13;
unsigned int chan5 : 13;
unsigned int chan6 : 13;
unsigned int chan7 : 13;
} __attribute__ ((__packed__)) crsfPayloadSubsetRcChannels13Packed_t;

typedef struct crsfPayloadLinkStatistics_s {
uint8_t uplinkRSSIAnt1;
uint8_t uplinkRSSIAnt2;
Expand Down Expand Up @@ -223,6 +266,105 @@ STATIC_UNIT_TESTED uint8_t crsfFrameStatus(rxRuntimeConfig_t *rxRuntimeConfig)
crsfChannelData[15] = rcChannels->chan15;
return RX_FRAME_COMPLETE;
}
else if(crsfFrame.frame.type == CRSF_FRAMETYPE_SUBSET_RC_CHANNELS_PACKED) {
const uint8_t crc = crsfFrameCRC();
const crsfPayloadSubsetRcChannelsHeaderPacked_t* rcChannelsHeader = (crsfPayloadSubsetRcChannelsHeaderPacked_t*)(&crsfFrame.frame.payload);
const crsfPayloadSubsetRcChannels11Packed_t* rcChannels11 = (crsfPayloadSubsetRcChannels11Packed_t*)(&crsfFrame.frame.payload + sizeof(crsfPayloadSubsetRcChannelsHeaderPacked_t));
const crsfPayloadSubsetRcChannels12Packed_t* rcChannels12 = (crsfPayloadSubsetRcChannels12Packed_t*)(&crsfFrame.frame.payload + sizeof(crsfPayloadSubsetRcChannelsHeaderPacked_t));
const crsfPayloadSubsetRcChannels13Packed_t* rcChannels13 = (crsfPayloadSubsetRcChannels13Packed_t*)(&crsfFrame.frame.payload + sizeof(crsfPayloadSubsetRcChannelsHeaderPacked_t));

int payloadSize = crsfFrame.frame.frameLength - CRSF_FRAME_LENGTH_TYPE_CRC; // TYPE_CRC or _CRC?
if (crc != crsfFrame.frame.payload[payloadSize]) {
return RX_FRAME_PENDING;
}

int channelCount = 0;

switch(rcChannelsHeader->resolution) {
case CRSF_11_BIT:
if((payloadSize * 8) % 11 != 0) {
return RX_FRAME_PENDING;
}

channelCount = payloadSize * 8 / 11;
break;
case CRSF_12_BIT:
if((payloadSize * 8) % 12 != 0) {
return RX_FRAME_PENDING;
}

channelCount = payloadSize * 8 / 12;
break;
case CRSF_13_BIT:
if((payloadSize * 8) % 13 != 0) {
return RX_FRAME_PENDING;
}

channelCount = payloadSize * 8 / 13;
break;
default:
return RX_FRAME_PENDING;
}

if(crsfFrame.frame.frameLength != payloadSize + CRSF_FRAME_LENGTH_TYPE_CRC || channelCount == 0) { // TYPE_CRC or _CRC?
return RX_FRAME_PENDING;
}

int firstChannel = rcChannelsHeader->firstChannel;
switch(rcChannelsHeader->resolution) {
case CRSF_11_BIT:
for (int i = 0; i < channelCount; rcChannels11++) {
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan0;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan1;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan3;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan4;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan5;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan6;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels11->chan7;
}
return RX_FRAME_COMPLETE;
case CRSF_12_BIT:
for (int i = 0; i < channelCount; rcChannels12++) {
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels12->chan0 >> 1; // Drop 1 bit to match 11 bit range
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels12->chan1 >> 1;
}

return RX_FRAME_COMPLETE;
case CRSF_13_BIT:
for (int i = 0; i < channelCount; rcChannels13++) {
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan0 >> 2; // Drop 2 bits to match 11 bit range
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan1 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan2 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan3 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan4 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan5 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan6 >> 2;
if(firstChannel + i < CRSF_MAX_CHANNEL)
crsfChannelData[firstChannel + i++] = rcChannels13->chan7 >> 2;
}
return RX_FRAME_COMPLETE;
default:
return RX_FRAME_PENDING;
}
}
else if (crsfFrame.frame.type == CRSF_FRAMETYPE_LINK_STATISTICS) {
// CRC includes type and payload of each frame
const uint8_t crc = crsfFrameCRC();
Expand Down Expand Up @@ -272,6 +414,8 @@ STATIC_UNIT_TESTED uint16_t crsfReadRawRC(const rxRuntimeConfig_t *rxRuntimeConf
* scale factor = (2012-988) / (1811-172) = 0.62477120195241
* offset = 988 - 172 * 0.62477120195241 = 880.53935326418548
*/

// TODO: different scaling for different resolutions. Currently dropping everything down to 11bits
return (crsfChannelData[chan] * 1024 / 1639) + 881;
}

Expand Down
1 change: 1 addition & 0 deletions src/main/rx/crsf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,7 @@ typedef enum {
CRSF_FRAMETYPE_BATTERY_SENSOR = 0x08,
CRSF_FRAMETYPE_LINK_STATISTICS = 0x14,
CRSF_FRAMETYPE_RC_CHANNELS_PACKED = 0x16,
CRSF_FRAMETYPE_SUBSET_RC_CHANNELS_PACKED = 0x17,
CRSF_FRAMETYPE_ATTITUDE = 0x1E,
CRSF_FRAMETYPE_FLIGHT_MODE = 0x21,
// Extended Header Frames, range: 0x28 to 0x96
Expand Down
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