HAL_ChibiOS: hold write lock for unbuffered writes

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -210,9 +210,11 @@ void UARTDriver::dma_tx_deallocate(void)
 void UARTDriver::tx_complete(void* self, uint32_t flags)
 {
     UARTDriver* uart_drv = (UARTDriver*)self;
-    uart_drv->dma_handle->unlock_from_IRQ();
-    uart_drv->_last_write_completed_us = AP_HAL::micros();
-    uart_drv->tx_bounce_buf_ready = true;
+    if (!uart_drv->tx_bounce_buf_ready) {
+        uart_drv->dma_handle->unlock_from_IRQ();
+        uart_drv->_last_write_completed_us = AP_HAL::micros();
+        uart_drv->tx_bounce_buf_ready = true;
+    }
 }
 
 
@@ -401,6 +403,9 @@ size_t UARTDriver::write(const uint8_t *buffer, size_t size)
 
     size_t ret = _writebuf.write(buffer, size);
     if (unbuffered_writes) {
+        if (ret != size) {
+            hal.console->printf("ret=%d size=%d\n", (int)ret, (int)size);
+        }
         write_pending_bytes();
     }
     chMtxUnlock(&_write_mutex);
@@ -431,6 +436,9 @@ void UARTDriver::write_pending_bytes_DMA(uint32_t n)
     if (!tx_bounce_buf_ready && txdma) {
         if (!(txdma->stream->CR & STM32_DMA_CR_EN)) {
             if (txdma->stream->NDTR == 0) {
+                hal.console->printf("ISR complete %u took %u\n",
+                                    AP_HAL::millis(),
+                                    AP_HAL::micros() - _last_write_started_us);
                 tx_bounce_buf_ready = true;
                 _last_write_completed_us = AP_HAL::micros();
                 dma_handle->unlock();
@@ -459,6 +467,7 @@ void UARTDriver::write_pending_bytes_DMA(uint32_t n)
     dmamode |= STM32_DMA_CR_PL(0);
     dmaStreamSetMode(txdma, dmamode | STM32_DMA_CR_DIR_M2P |
                      STM32_DMA_CR_MINC | STM32_DMA_CR_TCIE);
+    _last_write_started_us = AP_HAL::micros();
     dmaStreamEnable(txdma);
 }
 
@@ -608,10 +617,16 @@ void UARTDriver::_timer_tick(void)
         }
     }
 
-    if (!unbuffered_writes) {
+    if (unbuffered_writes) {
         // now send pending bytes. If we are doing "unbuffered" writes
-        // then the send happens as soon as the bytes are provided by
-        // the write() call, and no writes are done in the timer tick
+        // then the send normally happens as soon as the bytes are
+        // provided by the write() call, but if the write is larger
+        // than the DMA buffer size then there can be extra bytes to
+        // send here, and they must be sent with the write lock held
+        chMtxLock(&_write_mutex);
+        write_pending_bytes();
+        chMtxUnlock(&_write_mutex);
+    } else {
         write_pending_bytes();
     }