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HAL_ChibiOS: minimise DMA TX latency on contended UARTs

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try to prevent long delays on other users of a DMA channel
This commit is contained in:
Andrew Tridgell 2018-03-14 19:51:04 +11:00
parent a86e85c6b2
commit a64819cbf2
2 changed files with 30 additions and 6 deletions
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33
libraries/AP_HAL_ChibiOS/UARTDriver.cpp
View File

@ -519,12 +519,12 @@ bool UARTDriver::wait_timeout(uint16_t n, uint32_t timeout_ms)
}
/*
write out pending bytes with DMA
check for DMA completed for TX
*/
void UARTDriver::write_pending_bytes_DMA(uint32_t n)
void UARTDriver::check_dma_tx_completion(void)
{
chSysLock();
if (!tx_bounce_buf_ready && txdma) {
if (!tx_bounce_buf_ready) {
if (!(txdma->stream->CR & STM32_DMA_CR_EN)) {
if (txdma->stream->NDTR == 0) {
tx_bounce_buf_ready = true;
@ -533,12 +533,19 @@ void UARTDriver::write_pending_bytes_DMA(uint32_t n)
}
}
}
chSysUnlock();
}
/*
write out pending bytes with DMA
*/
void UARTDriver::write_pending_bytes_DMA(uint32_t n)
{
check_dma_tx_completion();
if (!tx_bounce_buf_ready) {
chSysUnlock();
return;
}
chSysUnlock();
/* TX DMA channel preparation.*/
_writebuf.advance(tx_len);
@ -550,6 +557,18 @@ void UARTDriver::write_pending_bytes_DMA(uint32_t n)
tx_len = 0;
return;
}
if (dma_handle->has_contention()) {
/*
someone else is using this same DMA channel. To reduce
latency we will drop the TX size with DMA on this UART to
keep TX times below 250us. This can still suffer from long
times due to CTS blockage
*/
uint32_t max_tx_bytes = 1 + (_baudrate * 250UL / 1000000UL);
if (tx_len > max_tx_bytes) {
tx_len = max_tx_bytes;
}
}
tx_bounce_buf_ready = false;
osalDbgAssert(txdma != nullptr, "UART TX DMA allocation failed");
dmaStreamSetMemory0(txdma, tx_bounce_buf);
@ -605,6 +624,10 @@ void UARTDriver::write_pending_bytes(void)
{
uint32_t n;
if (sdef.dma_tx) {
check_dma_tx_completion();
}
// write any pending bytes
n = _writebuf.available();
if (n <= 0) {

3
libraries/AP_HAL_ChibiOS/UARTDriver.h
View File

@ -124,7 +124,7 @@ private:
bool _rts_is_active;
uint32_t _last_write_completed_us;
uint32_t _first_write_started_us;
// set to true for unbuffered writes (low latency writes)
bool unbuffered_writes;
@ -136,6 +136,7 @@ private:
void dma_tx_deallocate(void);
void update_rts_line(void);
void check_dma_tx_completion(void);
void write_pending_bytes_DMA(uint32_t n);
void write_pending_bytes_NODMA(uint32_t n);
void write_pending_bytes(void);