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Ensured there is sufficient time to send a telemetry frame

This commit is contained in:
Martin Budden 2016-11-16 09:11:15 +00:00
parent 5d9c22e823
commit 3c5dd1604e
1 changed files with 9 additions and 5 deletions
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14
src/main/rx/crsf.c
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@ -41,7 +41,8 @@
#include "telemetry/telemetry.h"
#define CRSF_TIME_NEEDED_PER_FRAME_US 1500 //!! this needs checking
#define CRSF_TIME_NEEDED_PER_FRAME_US 1000
#define CRSF_TIME_BETWEEN_FRAMES_US 4000 // a frame is sent by the transmitter every 4 milliseconds
#define CRSF_DIGITAL_CHANNEL_MIN 172
#define CRSF_DIGITAL_CHANNEL_MAX 1811
@ -72,6 +73,8 @@ static uint8_t telemetryBufLen = 0;
* Assume a max payload of 32 bytes (needs confirming with TBS), so max frame size of 36 bytes
* A 36 byte frame can be transmitted in 771 microseconds.
*
* CRSF_TIME_NEEDED_PER_FRAME_US is set conservatively at 1000 microseconds
*
* Every frame has the structure:
* <Device address> <Frame length> < Type> <Payload> < CRC>
*
@ -204,10 +207,11 @@ void crsfRxSendTelemetryData(void)
{
// if there is telemetry data to write
if (telemetryBufLen > 0) {
// check that we are not currently receiving data
const uint32_t now = micros();
if (now > crsfFrameStartAt + CRSF_TIME_NEEDED_PER_FRAME_US) {
// any incoming frames will be complete, so it is OK to write to shared serial port
// check that we are not currently receiving data (ie in the middle of an RX frame)
// and that there is time to send the telemetry frame before the next RX frame arrives
const uint32_t timeSinceStartOfFrame = micros() - crsfFrameStartAt;
if ((timeSinceStartOfFrame > CRSF_TIME_NEEDED_PER_FRAME_US)
&& (timeSinceStartOfFrame < CRSF_TIME_BETWEEN_FRAMES_US - CRSF_TIME_NEEDED_PER_FRAME_US)) {
serialWriteBuf(serialPort, telemetryBuf, telemetryBufLen);
telemetryBufLen = 0; // reset telemetry buffer
}