pios_usart: Add flag field and DMA hint.

Author: glowtape

flight/PiOS/STM32/inc/pios_usart_priv.h

@@ -34,6 +34,9 @@
 #include <pios_stm32.h>
 #include "pios_usart.h"
 
+#define PIOS_USART_ALLOW_RECEIVE_DMA	0x1
+#define PIOS_USART_ALLOW_TRANSMIT_DMA	0x2
+
 extern const struct pios_com_driver pios_usart_com_driver;
 
 #if defined(STM32F4XX)
@@ -63,6 +66,7 @@ struct pios_usart_params {
 	bool tx_invert;
 	bool rxtx_swap;
 	bool single_wire;
+	uint8_t flags;
 };
 
 extern int32_t PIOS_USART_Init(uintptr_t * usart_id, const struct pios_usart_cfg * cfg, struct pios_usart_params * params);

flight/PiOS/STM32F4xx/pios_usart.c

@@ -226,7 +226,7 @@ int32_t PIOS_USART_Init(uintptr_t * usart_id, const struct pios_usart_cfg * cfg,
 	// FIXME XXX Clear / reset uart here - sends NUL char else
 
 	/* Check DMA transmit configuration and prepare DMA. */
-	if (cfg->dma_send) {
+	if (cfg->dma_send && (params->flags & PIOS_USART_ALLOW_TRANSMIT_DMA)) {
 		usart_dev->dma_send_buffer = (uint32_t)PIOS_malloc(PIOS_USART_DMA_SEND_BUFFER_SZ);
 
 		if (usart_dev->dma_send_buffer) {
@@ -237,7 +237,7 @@ int32_t PIOS_USART_Init(uintptr_t * usart_id, const struct pios_usart_cfg * cfg,
 	}
 
 	/* Check DMA receive configuration, and setup and start DMA. */
-	if (cfg->dma_recv) {
+	if (cfg->dma_recv && (params->flags & PIOS_USART_ALLOW_RECEIVE_DMA)) {
 		usart_dev->dma_recv_buffer = (uint32_t)PIOS_malloc(PIOS_USART_DMA_RECV_BUFFER_SZ);
 
 		if (usart_dev->dma_recv_buffer) {