Merge pull request #449 from madcowswe/fix_uart_latency

Increase UART polling frequency from 1kHz to 8kHz

Firmware/MotorControl/axis.hpp

@@ -163,6 +163,10 @@ public:
             // TODO: change arming logic to arm after waiting
             bool main_continue = update_handler();
 
+            if (axis_num_ == 0) {
+                uart_poll(); // TODO: move to board-level control loop once it exists
+            }
+
             // Check we meet deadlines after queueing
             ++loop_counter_;
 

Firmware/MotorControl/odrive_main.h

@@ -12,6 +12,7 @@
 #include <fibre/protocol.hpp>
 #include <communication/interface_usb.h>
 #include <communication/interface_i2c.h>
+#include <communication/interface_uart.h>
 extern "C" {
 #endif
 

Firmware/communication/interface_uart.cpp

@@ -62,9 +62,7 @@ static void uart_server_thread(void * ctx) {
     (void) ctx;
 
     for (;;) {
-        osDelay(1);
-
-        // Check for UART errors and restart recieve DMA transfer if required
+        // Check for UART errors and restart receive DMA transfer if required
         if (huart4.RxState != HAL_UART_STATE_BUSY_RX) {
             HAL_UART_AbortReceive(&huart4);
             HAL_UART_Receive_DMA(&huart4, dma_rx_buffer, sizeof(dma_rx_buffer));
@@ -92,11 +90,17 @@ static void uart_server_thread(void * ctx) {
                     new_rcv_idx - dma_last_rcv_idx, uart4_stream_output);
             dma_last_rcv_idx = new_rcv_idx;
         }
-    };
+
+        // The thread is woken up by the control loop at 8kHz. This should be
+        // enough for most applications.
+        // At 1Mbaud/s that corresponds to at most 12.5 bytes which can arrive
+        // during the sleep period.
+        osThreadSuspend(nullptr);
+    }
 }
 
 void start_uart_server() {
-    // DMA is set up to recieve in a circular buffer forever.
+    // DMA is set up to receive in a circular buffer forever.
     // We dont use interrupts to fetch the data, instead we periodically read
     // data out of the circular buffer into a parse buffer, controlled by a state machine
     HAL_UART_Receive_DMA(&huart4, dma_rx_buffer, sizeof(dma_rx_buffer));
@@ -107,6 +111,10 @@ void start_uart_server() {
     uart_thread = osThreadCreate(osThread(uart_server_thread_def), NULL);
 }
 
+void uart_poll() {
+    osThreadResume(uart_thread);
+}
+
 void HAL_UART_TxCpltCallback(UART_HandleTypeDef* huart) {
     osSemaphoreRelease(sem_uart_dma);
 }

Firmware/communication/interface_uart.h

@@ -14,6 +14,7 @@ extern osThreadId uart_thread;
 extern const uint32_t stack_size_uart_thread;
 
 void start_uart_server(void);
+void uart_poll(void);
 
 #ifdef __cplusplus
 }