Merge pull request 'usart' (#1) from usart into rework

Reviewed-on: https://git.steins7.ovh/Steins7/stm32f1xx_HBL/pulls/1

drv/dma.c

@@ -19,9 +19,9 @@
 //--local definitions-----------------------------------------------------------
 
 static void configure_dma(volatile struct DMA* dma, enum DmaChannel channel,
-		enum DmaConfig config_mask, volatile void* periph, volatile void* mem,
-		uint16_t size);
-
+		enum DmaConfig config_mask, volatile void* periph);
+static void start_dma(volatile struct DMA* dma, enum DmaChannel channel,
+		volatile void* mem, uint16_t size);
 
 //--local variables-------------------------------------------------------------
 
@@ -36,8 +36,8 @@ static volatile void* dma2_cb_params[5];
 //--public functions------------------------------------------------------------
 
 void dma_configure(enum DmaPeriph dma, enum DmaChannel channel,
-		enum DmaConfig config_mask, volatile void* periph, volatile void* mem,
-		uint16_t size, DmaCallback callback, volatile void* cb_param)
+		enum DmaConfig config_mask, volatile void* periph,
+		DmaCallback callback, volatile void* cb_param)
 {
 	//reset peripheral first, to ensure proper configuration
 	dma_reset(dma, channel);
@@ -45,7 +45,7 @@ void dma_configure(enum DmaPeriph dma, enum DmaChannel channel,
 	switch (dma) {
 		case DMA_PERIPH_1:
 			rcc_enable(RCC_AHB_DMA1, RCC_APB1_NONE, RCC_APB2_NONE);
-			configure_dma(dma1, channel, config_mask, periph, mem, size);
+			configure_dma(dma1, channel, config_mask, periph);
 			if (callback) {
 				dma1_callbacks[channel] = callback;
 				dma1_cb_params[channel] = cb_param;
@@ -54,7 +54,7 @@ void dma_configure(enum DmaPeriph dma, enum DmaChannel channel,
 			break;
 		case DMA_PERIPH_2:
 			rcc_enable(RCC_AHB_DMA2, RCC_APB1_NONE, RCC_APB2_NONE);
-			configure_dma(dma2, channel, config_mask, periph, mem, size);
+			configure_dma(dma2, channel, config_mask, periph);
 			if (callback) {
 				dma2_callbacks[channel] = callback;
 				dma2_cb_params[channel] = cb_param;
@@ -95,14 +95,21 @@ void dma_reset(enum DmaPeriph dma, enum DmaChannel channel)
 	regs->CPAR = 0;
 }
 
-void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel)
+void dma_start(enum DmaPeriph dma, enum DmaChannel channel,
+		volatile void* mem, uint16_t size)
 {
 	switch (dma) {
 		case DMA_PERIPH_1:
-			nvic_enable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
+			if (dma1_callbacks[channel]) {
+				nvic_enable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
+			}
+			start_dma(dma1, channel, mem, size);
 			break;
 		case DMA_PERIPH_2:
-			nvic_enable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
+			if (dma2_callbacks[channel]) {
+				nvic_enable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
+			}
+			start_dma(dma2, channel, mem, size);
 			break;
 		default:
 			return;
@@ -110,19 +117,19 @@ void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel)
 	}
 }
 
-void dma_enable(enum DmaPeriph dma, enum DmaChannel channel)
+void dma_stop(enum DmaPeriph dma, enum DmaChannel channel)
 {
 	switch (dma) {
 		case DMA_PERIPH_1:
-			reg_set(dma1->CHANNELS[channel].CCR, DMA_CCR_EN);
+			reg_reset(dma1->CHANNELS[channel].CCR, DMA_CCR_EN);
 			if (dma1_callbacks[channel]) {
-				nvic_enable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
+				nvic_disable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
 			}
 			break;
 		case DMA_PERIPH_2:
-			reg_set(dma2->CHANNELS[channel].CCR, DMA_CCR_EN);
+			reg_reset(dma2->CHANNELS[channel].CCR, DMA_CCR_EN);
 			if (dma2_callbacks[channel]) {
-				nvic_enable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
+				nvic_disable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
 			}
 			break;
 		default:
@@ -146,20 +153,14 @@ void dma_enter_critical(enum DmaPeriph dma, enum DmaChannel channel)
 	}
 }
 
-void dma_disable(enum DmaPeriph dma, enum DmaChannel channel)
+void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel)
 {
 	switch (dma) {
 		case DMA_PERIPH_1:
-			reg_reset(dma1->CHANNELS[channel].CCR, DMA_CCR_EN);
-			if (dma1_callbacks[channel]) {
-				nvic_disable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
-			}
+			nvic_enable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
 			break;
 		case DMA_PERIPH_2:
-			reg_reset(dma2->CHANNELS[channel].CCR, DMA_CCR_EN);
-			if (dma2_callbacks[channel]) {
-				nvic_disable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
-			}
+			nvic_enable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
 			break;
 		default:
 			return;
@@ -184,22 +185,34 @@ uint16_t dma_get_remaining(enum DmaPeriph dma, enum DmaChannel channel)
 
 //--local functions-------------------------------------------------------------
 
+/**
+ * Applies the given configuration mask to the given DMA channel
+ */
 static void configure_dma(volatile struct DMA* dma, enum DmaChannel channel,
-		enum DmaConfig config_mask, volatile void* periph, volatile void* mem,
-		uint16_t size)
+		enum DmaConfig config_mask, volatile void* periph)
 {
 	volatile struct DMA_CHANNEL* regs = &dma->CHANNELS[channel];
 
 	//registers should already be at reset value, apply new config
 	regs->CCR.word = config_mask;
-	reg_write(regs->CNDTR, DMA_CNDTR_NDT, size);
 	regs->CPAR = (uint32_t)periph;
-	regs->CMAR = (uint32_t)mem;
-
-	//only enable channel when everything is configured
-	reg_set(regs->CCR, DMA_CCR_EN);
 }
 
+/**
+ * Starts the given DMA channel using the given parameters
+ */
+static void start_dma(volatile struct DMA* dma, enum DmaChannel channel,
+		volatile void* mem, uint16_t size)
+{
+	volatile struct DMA_CHANNEL* regs = &dma->CHANNELS[channel];
+
+	//registers should already be configured, apply transfer config
+	reg_write(regs->CNDTR, DMA_CNDTR_NDT, size);
+	regs->CMAR = (uint32_t)mem;
+
+	//only start transfer when everything is configured
+	reg_set(regs->CCR, DMA_CCR_EN);
+}
 
 //--ISRs------------------------------------------------------------------------
 

drv/dma.h

@@ -15,11 +15,19 @@
 
 //--type definitions------------------------------------------------------------
 
+/**
+ * Available DMA peripherals. Note that some of these peripherals may not be
+ * available on all chips
+ */
 enum DmaPeriph {
 	DMA_PERIPH_1,
 	DMA_PERIPH_2,
 };
 
+/**
+ * Available DMA channels. Note that some of these channels may not be
+ * available on all chips and all DMA peripheral
+ */
 enum DmaChannel {
 	DMA_CHANNEL_1 = 0,
 	DMA_CHANNEL_2,
@@ -30,6 +38,9 @@ enum DmaChannel {
 	DMA_CHANNEL_7, //not available for DMA 2
 };
 
+/**
+ * Configuration options for memory-to-peripheral transfers
+ */
 enum DmaConfig {
 	DMA_CONFIG_IRQ_COMPLETE = (0x1 <<  1),
 	DMA_CONFIG_IRQ_HALF     = (0x1 <<  2),
@@ -51,6 +62,9 @@ enum DmaConfig {
 	DMA_CONFIG_PRIO_VHIGH   = (0x3 << 12),
 };
 
+/**
+ * Configuration options for memory-to-memory transfers
+ */
 enum DmaConfigM2M {
 	DMA_CONFIG_M2M_IRQ_COMPLETE = (0x1 <<  1),
 	DMA_CONFIG_M2M_IRQ_HALF     = (0x1 <<  2),
@@ -69,35 +83,96 @@ enum DmaConfigM2M {
 	DMA_CONFIG_M2M_PRIO_VHIGH   = (0x3 << 12),
 };
 
+/**
+ * Available sources for a DMA IRQ. These sources can be enabled independently
+ * in the DMA configuration.
+ */
 enum DmaIRQSource {
 	DMA_IRQ_SOURCE_COMPLETE = (0x1 << 1),
 	DMA_IRQ_SOURCE_HALF     = (0x1 << 2),
 	DMA_IQR_SOURCE_ERROR    = (0x2 << 3),
 };
 
+/**
+ * Prototype of the IRQ callbacks that the applicative code can provide
+ */
 typedef void (*DmaCallback)(enum DmaIRQSource, volatile void* param);
 
+/**
+ * Generic struct used to share DAM configs between peripheral drivers and
+ * services providing DMA interfaces
+ */
+struct DmaParam {
+	void* periph;
+	enum DmaConfig config;    //DMA config, must correspond to peripheral
+	enum DmaPeriph dma;       //DMA peripheral, must correspond to peripheral
+	enum DmaChannel channel;  //DMA channel, must correspond to peripheral
+};
+
 
 //--functions-------------------------------------------------------------------
 
+/**
+ * Configures the given DMA channel with the provided configuration, to perform
+ * a transfer to or from the given peripheral register. The specified callback,
+ * if any, will be called on the enabled IRQ sources, with the specified
+ * parameter, if any.
+ *
+ * This function doesn't initiate transfers, use dma_start() for that
+ */
 void dma_configure(enum DmaPeriph dma, enum DmaChannel channel,
-		enum DmaConfig config_mask, volatile void* periph, volatile void* mem,
-		uint16_t size, DmaCallback callback, volatile void* cb_param);
+		enum DmaConfig config_mask, volatile void* periph,
+		DmaCallback callback, volatile void* cb_param);
 
+/**
+ * Unimplemented
+ */
 void dma_configure_mem2mem(enum DmaPeriph dma, enum DmaChannel channel,
 		enum DmaConfigM2M config_mask, const void* src, void* dest,
 		uint16_t size, DmaCallback callback, void* cb_param);
 
+/**
+ * Resets the given DMA channel, restoring the default configuration and
+ * disabling it
+ */
 void dma_reset(enum DmaPeriph dma, enum DmaChannel channel);
 
-void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel);
+/**
+ * Initiate a transfer on the given DMA channel, to or from the given memory
+ * address, and of the specified size.
+ *
+ * Should only be used after the channel has been configured through
+ * dma_configure()
+ * All transfers started must be eventually stopped, or the channel reset, for
+ * proper IRQ behavior.
+ */
+void dma_start(enum DmaPeriph dma, enum DmaChannel channel,
+		volatile void* mem, uint16_t size);
 
-void dma_enable(enum DmaPeriph dma, enum DmaChannel channel);
+/**
+ * Stops a transfer on the given DMA channel. If the transfer has already
+ * ended, properly shutdown the channel. Configuration is not lost after calling
+ * this function and dma_start() may be called again
+ */
+void dma_stop(enum DmaPeriph dma, enum DmaChannel channel);
 
+/**
+ * Enters a DMA critical section, disabling the given channel's IRQs until
+ * dma_exit_critical() is called
+ */
 void dma_enter_critical(enum DmaPeriph dma, enum DmaChannel channel);
 
-void dma_disable(enum DmaPeriph dma, enum DmaChannel channel);
+/**
+ * Exists a DMA critical section previously entered through
+ * dma_enter_critical(). Reenables the given channel's IRQs
+ */
+void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel);
 
+/**
+ * Returns the remaining number of bytes to be transmitted while a transfer is
+ * running. When no transfer is running, returns the number of bytes to transfer
+ * next
+ */
 uint16_t dma_get_remaining(enum DmaPeriph dma, enum DmaChannel channe);
 
 

drv/dma_mbuf.c

@@ -1,143 +0,0 @@
-/** @file dma_mbuf.h
- * Module handling Direct Memory Access controller's multibuffer system
- *
- * The module provides a convenient tool to send data to a peripheral in a
- * buffered, low-altency, low-cpu usage, non-blocking way
- */
-
-//--includes--------------------------------------------------------------------
-
-#include "dma_mbuf.h"
-
-
-//--local definitions-----------------------------------------------------------
-
-#define DMA_CONFIG (DMA_CONFIG_IRQ_COMPLETE | DMA_CONFIG_FROM_MEM \
-					| DMA_CONFIG_INC_MEM | DMA_CONFIG_PSIZE_8BITS \
-					| DMA_CONFIG_MSIZE_8BITS)
-
-static void mbuf_callback(enum DmaIRQSource src, volatile void* param);
-
-//take last 2 bytes of a buffer and assemble them store the current byte index
-#define byte_index (((uint16_t**)buffer->buffers) \
-		[buffer->buffer_index][buffer->buffer_size/2])
-#define dma_byte_index (((uint16_t**)buffer->buffers) \
-		[buffer->dma_buffer_index][buffer->buffer_size/2])
-
-
-//--local variables-------------------------------------------------------------
-
-//--public functions------------------------------------------------------------
-
-void dma_mbuf_configure(volatile struct DmaMultiBuffer* buffer, void** buffers,
-		volatile void* dest, uint16_t buffer_size, uint8_t buffer_nb,
-		enum DmaPeriph dma, enum DmaChannel channel, enum DmaConfig priority)
-{
-	#warning "check for null ptr"
-
-	buffer->buffers = buffers;
-	buffer->dest = dest;
-
-	buffer->buffer_size = buffer_size - 2;
-
-	buffer->buffer_nb = buffer_nb;
-	buffer->free_buffer_nb = buffer_nb - 1;
-	buffer->buffer_index = 0;
-	buffer->dma_buffer_index = 0;
-
-	buffer->dma = dma;
-	buffer->channel = channel;
-	buffer->config = DMA_CONFIG | priority;
-
-	for (uint8_t i=0; i<buffer->buffer_nb; ++i) {
-		for (uint16_t j=0; j<buffer->buffer_size + 2; ++j) {
-			((uint8_t**)buffer->buffers)[i][j] = 0;
-		}
-	}
-}
-
-uint32_t dma_mbuf_write_byte(volatile struct DmaMultiBuffer* buffer,
-		uint8_t byte)
-{
-	dma_enter_critical(buffer->dma, buffer->channel);
-
-	//if the current buffer is full, we need to switch it with an empty one
-	volatile uint16_t index = byte_index;
-	if (byte_index >= buffer->buffer_size) {
-
-		//if all buffer full, give up
-		if (buffer->free_buffer_nb == 0) {
-			dma_exit_critical(buffer->dma, buffer->channel);
-			return 1;
-		}
-
-		++buffer->buffer_index;
-		if (buffer->buffer_index >= buffer->buffer_nb) {
-			buffer->buffer_index = 0;
-		}
-		--buffer->free_buffer_nb;
-
-		byte_index = 0;
-	}
-
-	//write the byte
-	uint8_t** buffers = (uint8_t**)buffer->buffers;
-	buffers[buffer->buffer_index][byte_index] = byte;
-	++byte_index;
-	++index;
-
-	dma_exit_critical(buffer->dma, buffer->channel);
-	return 0;
-}
-
-void dma_mbuf_refresh(volatile struct DmaMultiBuffer* buffer)
-{
-	//no more data to send, stop here
-	if (buffer->dma_buffer_index == buffer->buffer_index
-			&& byte_index == 0) {
-		return;
-	}
-
-	//else start a new transfer
-	dma_configure(buffer->dma, buffer->channel, buffer->config, buffer->dest,
-			buffer->buffers[buffer->dma_buffer_index],
-			dma_byte_index, mbuf_callback, buffer);
-
-	//if the newly transfering buffer was being written to, switch the current
-	//buffer. Since we just ended a transfer, the next buffer should be empty
-	if (buffer->dma_buffer_index == buffer->buffer_index)
-	{
-		++buffer->buffer_index;
-		if (buffer->buffer_index >= buffer->buffer_nb) {
-			buffer->buffer_index = 0;
-		}
-		--buffer->free_buffer_nb;
-
-		byte_index = 0;
-	}
-
-	return;
-}
-
-
-//--local functions-------------------------------------------------------------
-
-/**
- * Callback called on DMA TX tranfert's completion. Checks for any remaining
- * data to send. If any, starts a new transfer, else stop the DMA
- */
-static void mbuf_callback(enum DmaIRQSource src, volatile void* param)
-{
-	(void)src; //only transfer complete expected
-	volatile struct DmaMultiBuffer* buffer = param;
-
-	//increment DMA's buffer since the last once has already been sent
-	++buffer->dma_buffer_index;
-	if (buffer->dma_buffer_index >= buffer->buffer_nb) {
-		buffer->dma_buffer_index = 0;
-	}
-	++buffer->free_buffer_nb;
-
-	dma_mbuf_refresh(param);
-}
-

drv/dma_mbuf.h

@@ -1,78 +0,0 @@
-/** @file dma_mbuf.h
- * Module handling Direct Memory Access controller's multibuffer system
- *
- * The module provides a convenient tool to send data to a peripheral in a
- * buffered, low-altency, low-cpu usage, non-blocking way
- */
-
-#ifndef _DMA_MBUF_H_
-#define _DMA_MBUF_H_
-
-//--includes--------------------------------------------------------------------
-
-#include "dma.h"
-
-
-//--type definitions------------------------------------------------------------
-
-/**
- * Struct used by the multibuffer system. This system allows bufferized writes
- * to a peripheral with no latency, minimal cpu usage and customisable buffer
- * sizes
- */
-struct DmaMultiBuffer {
-	void** buffers;           //list of buffers to write to
-	volatile void* dest;      //destination peripheral register
-
-	uint16_t buffer_size;     //size of a single buffer
-
-	uint8_t buffer_nb;        //total number of buffers
-	uint8_t free_buffer_nb;   //number of buffers not currently used
-	uint8_t buffer_index;     //index of the current buffer
-	uint8_t dma_buffer_index; //index of the DMA's current buffer
-
-	enum DmaPeriph dma;       //DMA peripheral, must correspond to peripheral
-	enum DmaChannel channel;  //DMA channel, must correspond to peripheral
-	enum DmaConfig config;    //DMA config, must correspond to peripheral
-};
-
-
-//--functions-------------------------------------------------------------------
-
-/**
- * Configure a DMA multibuffer for a single DMA channel. A list of buffers is
- * used to allow concurent write and DMA tranfers to the specified destination
- * wich must be a peripheral. The DMA's priority is also given as parameters.
- * The peripheral's specific configuration must be handled separately. 2 bytes
- * are reserved in each buffer for index storage.
- *
- * This system needs to be started manually: dma_mbuf_refresh() should be called
- * whenever a DMA transfer can be started. This can be done manually after
- * filling up the buffer. Transfers will then automatically be started as long
- * as there are bytes in the buffer. See the usart module for an usage exemple
- */
-void dma_mbuf_configure(volatile struct DmaMultiBuffer* buffer, void** buffers,
-		volatile void* dest, uint16_t buffer_size, uint8_t buffer_nb,
-        enum DmaPeriph dma, enum DmaChannel channel, enum DmaConfig priority);
-
-/**
- * Write the given byte to the given buffer. Returns 0 if the write operation
- * was successfull, 1 otherwise. The function is non-blocking.
- *
- * Note: calling this function will not trigger a DMA transfer, see
- * dma_mbuf_refresh() to do that
- */
-uint32_t dma_mbuf_write_byte(volatile struct DmaMultiBuffer* buffer,
-		uint8_t byte);
-
-/**
- * Refresh the buffer state, checking for bytes to send and triggering a DMA
- * transfer if necessary. Should be called for the first transfer, any remaining
- * transfer will be handled automatically until there are no bytes left in the
- * buffer
- */
-void dma_mbuf_refresh(volatile struct DmaMultiBuffer* buffer);
-
-
-#endif //_DMA_MBUF_H_
-

drv/usart.c

@@ -8,14 +8,11 @@
 //--includes--------------------------------------------------------------------
 
 #include "usart.h"
-#include "nvic.h"
 #include "usart_regs.h"
 #include "reg.h"
 
 #include "rcc.h"
 #include "dma.h"
-#include "dma_mbuf.h"
-#include "dma_cbuf.h"
 
 #include "stddef.h"
 
@@ -27,19 +24,58 @@ static void configure_usart(volatile struct USART* regs,
 static void configure_baudrate(volatile struct USART* regs, uint32_t clock,
 		uint32_t baudrate);
 
+#define DMA_CONFIG (DMA_CONFIG_PSIZE_8BITS)
+
 
 //--local variables-------------------------------------------------------------
 
-static volatile struct USART* const usart1 = (struct USART*)USART1_BASE_ADDRESS;
-static volatile struct USART* const usart2 = (struct USART*)USART2_BASE_ADDRESS;
-static volatile struct USART* const usart3 = (struct USART*)USART3_BASE_ADDRESS;
+static volatile struct USART* const usarts[] = {
+	(struct USART*)USART1_BASE_ADDRESS,
+	(struct USART*)USART2_BASE_ADDRESS,
+	(struct USART*)USART3_BASE_ADDRESS,
+};
 
-static volatile struct DmaCircBuffer usart1_rx_buffer;
-static volatile struct DmaMultiBuffer usart1_tx_buffer;
-static volatile struct DmaCircBuffer usart2_rx_buffer;
-static volatile struct DmaMultiBuffer usart2_tx_buffer;
-static volatile struct DmaCircBuffer usart3_rx_buffer;
-static volatile struct DmaMultiBuffer usart3_tx_buffer;
+static const struct DmaParam usarts_rx_param[] = {
+	{
+		(void*)&usarts[USART_PERIPH_1]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_5,
+	},
+	{
+		(void*)&usarts[USART_PERIPH_2]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_6,
+	},
+	{
+		(void*)&usarts[USART_PERIPH_3]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_3,
+	},
+};
+
+static const struct DmaParam usarts_tx_param[] = {
+	{
+		(void*)&usarts[USART_PERIPH_1]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_4,
+	},
+	{
+		(void*)&usarts[USART_PERIPH_2]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_7,
+	},
+	{
+		(void*)&usarts[USART_PERIPH_3]->DR,
+		DMA_CONFIG,
+		DMA_PERIPH_1,
+		DMA_CHANNEL_2,
+	},
+};
 
 
 //--public functions------------------------------------------------------------
@@ -53,161 +89,77 @@ void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 	switch (periph) {
 		case USART_PERIPH_1:
 			rcc_enable(RCC_AHB_NONE, RCC_APB1_NONE, RCC_APB2_USART);
-			configure_baudrate(usart1, clocks.apb2_freq, baudrate);
-			configure_usart(usart1, config);
-			usart1_tx_buffer.buffers = NULL;
-			usart1_rx_buffer.buffer = NULL;
+			configure_baudrate(usarts[USART_PERIPH_1], clocks.apb2_freq,
+					baudrate);
+			configure_usart(usarts[USART_PERIPH_1], config);
 			break;
 		case USART_PERIPH_2:
 			rcc_enable(RCC_AHB_NONE, RCC_APB1_USART2, RCC_APB2_NONE);
-			configure_baudrate(usart2, clocks.apb1_freq, baudrate);
-			configure_usart(usart2, config);
-			usart2_tx_buffer.buffers = NULL;
-			usart2_rx_buffer.buffer = NULL;
+			configure_baudrate(usarts[USART_PERIPH_2], clocks.apb1_freq,
+					baudrate);
+			configure_usart(usarts[USART_PERIPH_2], config);
 			break;
 		case USART_PERIPH_3:
 			rcc_enable(RCC_AHB_NONE, RCC_APB1_USART3, RCC_APB2_NONE);
-			configure_baudrate(usart3, clocks.apb1_freq, baudrate);
-			configure_usart(usart3, config);
-			usart3_tx_buffer.buffers = NULL;
-			usart3_rx_buffer.buffer = NULL;
+			configure_baudrate(usarts[USART_PERIPH_3], clocks.apb1_freq,
+					baudrate);
+			configure_usart(usarts[USART_PERIPH_3], config);
 			break;
 		default:
 			break;
 	}
 }
 
-uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte)
-{
-	volatile struct USART* regs;
-	volatile struct DmaMultiBuffer* buffer;
-	enum NvicIrq irq;
-
-	switch (periph) {
-		case USART_PERIPH_1:
-			regs = usart1;
-			buffer = &usart1_tx_buffer;
-			irq = NVIC_IRQ_USART1;
-			break;
-		case USART_PERIPH_2:
-			regs = usart2;
-			buffer = &usart2_tx_buffer;
-			irq = NVIC_IRQ_USART2;
-			break;
-		case USART_PERIPH_3:
-			regs = usart3;
-			buffer = &usart3_tx_buffer;
-			irq = NVIC_IRQ_USART3;
-			break;
-		default:
-			return 1;
-			break;
-	}
-
-	if (buffer->buffers) {
-		//if the tx register is empty, there is no need to go through the dma
-		if (regs->SR.TC) {
-			reg_write(regs->DR, USART_DR_DR, byte);
-			//enable IRQ, disable DMA
-			reg_reset(regs->CR3, USART_CR3_DMAT);
-			reg_set(regs->CR1, USART_CR1_TXEIE);
-			nvic_enable(irq);
-			return 0;
-		} else {
-			return dma_mbuf_write_byte(buffer, byte);
-		}
-	} else {
-		//only write data if the tx register it empty, give up otherwise
-		if (regs->SR.TXE) {
-			reg_write(regs->DR, USART_DR_DR, byte);
-			return 0;
-		} else {
-			return 1;
-		}
-	}
-}
-
 uint32_t usart_read_byte(enum UsartPeriph periph, uint8_t* byte)
 {
-	volatile struct USART* regs;
-	volatile struct DmaCircBuffer* buffer;
-
-	switch (periph) {
-		case USART_PERIPH_1:
-			regs = usart1;
-			buffer = &usart1_rx_buffer;
-			break;
-		case USART_PERIPH_2:
-			regs = usart2;
-			buffer = &usart2_rx_buffer;
-			break;
-		case USART_PERIPH_3:
-			regs = usart3;
-			buffer = &usart3_rx_buffer;
-			break;
-		default:
-			return 1;
-			break;
+	if (periph > USART_PERIPH_3) {
+		return 1;
 	}
 
-	if (buffer->buffer) {
-		return dma_cbuf_read_byte(buffer, byte);
+	if (usarts[periph]->SR.RXNE) {
+		*byte = usarts[periph]->DR.DR;
+		return 0;
 	} else {
-		if (regs->SR.RXNE) {
-			*byte = regs->DR.DR;
-			return 0;
-		} else {
-			return 1;
-		}
+		return 1;
 	}
 }
 
-void usart_set_tx_buffer(enum UsartPeriph periph, uint8_t** buffers,
-		uint16_t buffer_size, uint8_t buffer_nb, enum DmaConfig priority)
+uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte)
 {
-	switch (periph) {
-		case USART_PERIPH_1:
-			dma_mbuf_configure(&usart1_tx_buffer, (void**)buffers, &usart1->DR,
-					buffer_size, buffer_nb, DMA_PERIPH_1, DMA_CHANNEL_4,
-					priority);
-			break;
-		case USART_PERIPH_2:
-			dma_mbuf_configure(&usart2_tx_buffer, (void**)buffers, &usart2->DR,
-					buffer_size, buffer_nb, DMA_PERIPH_1, DMA_CHANNEL_7,
-					priority);
-			break;
-		case USART_PERIPH_3:
-			dma_mbuf_configure(&usart3_tx_buffer, (void**)buffers, &usart3->DR,
-					buffer_size, buffer_nb, DMA_PERIPH_1, DMA_CHANNEL_2,
-					priority);
-			break;
+	if (periph > USART_PERIPH_3) {
+		return 1;
+	}
+
+	//only write data if the tx register it empty, give up otherwise
+	if (usarts[periph]->SR.TXE) {
+		reg_write(usarts[periph]->DR, USART_DR_DR, byte);
+		return 0;
+	} else {
+		return 1;
 	}
 }
 
-void usart_set_rx_buffer(enum UsartPeriph periph, uint8_t* buffer,
-		uint16_t size, enum DmaConfig priority)
+const struct DmaParam* usart_configure_rx_dma(enum UsartPeriph periph)
 {
-	switch (periph) {
-		case USART_PERIPH_1:
-			dma_cbuf_configure(&usart1_rx_buffer, buffer, (void*)&usart1->DR,
-					size, DMA_PERIPH_1, DMA_CHANNEL_5, priority);
-			reg_set(usart1->CR3, USART_CR3_DMAR);
-			break;
-		case USART_PERIPH_2:
-			dma_cbuf_configure(&usart2_rx_buffer, buffer, (void*)&usart2->DR,
-					size, DMA_PERIPH_1, DMA_CHANNEL_6, priority);
-			reg_set(usart2->CR3, USART_CR3_DMAR);
-			break;
-
-		case USART_PERIPH_3:
-			dma_cbuf_configure(&usart3_rx_buffer, buffer, (void*)&usart3->DR,
-					size, DMA_PERIPH_1, DMA_CHANNEL_3, priority);
-			reg_set(usart3->CR3, USART_CR3_DMAR);
-
-			break;
+	if (periph > USART_PERIPH_3) {
+		return nullptr;
 	}
+
+	reg_set(usarts[periph]->CR3, USART_CR3_DMAR);
+	return &usarts_rx_param[periph];
 }
 
+const struct DmaParam* usart_configure_tx_dma(enum UsartPeriph periph)
+{
+	if (periph > USART_PERIPH_3) {
+		return nullptr;
+	}
+
+	reg_set(usarts[periph]->CR3, USART_CR3_DMAT);
+	return &usarts_tx_param[periph];
+}
+
+
 //--local functions-------------------------------------------------------------
 
 /**
@@ -293,7 +245,7 @@ static void configure_usart(volatile struct USART* regs,
 
 /**
  * Configure the given registers with the given baudrate. Baudrate is dependant
- * on the peripheric's clock and may not be exact due to precision errors (see
+ * on the peripheral's clock and may not be exact due to precision errors (see
  * table 192 in documentation)
  */
 static void configure_baudrate(volatile struct USART* regs, uint32_t clock,
@@ -309,39 +261,3 @@ static void configure_baudrate(volatile struct USART* regs, uint32_t clock,
 	reg_write(regs->BRR, USART_BRR_DIV_Fraction, divider & 0xF);
 }
 
-
-//--ISRs------------------------------------------------------------------------
-
-void hdr_usart1(void)
-{
-	//disable the interrupt. It will be reenabled on a write if needed
-	nvic_clear_pending(NVIC_IRQ_USART1);
-	nvic_disable(NVIC_IRQ_USART1);
-	reg_reset(usart1->CR1, USART_CR1_TXEIE);
-	reg_set(usart1->CR3, USART_CR3_DMAT);
-
-	dma_mbuf_refresh(&usart1_tx_buffer);
-}
-
-void hdr_usart2(void)
-{
-	//disable the interrupt. It will be reenabled on a write if needed
-	nvic_clear_pending(NVIC_IRQ_USART2);
-	nvic_disable(NVIC_IRQ_USART2);
-	reg_reset(usart2->CR1, USART_CR1_TXEIE);
-	reg_set(usart2->CR3, USART_CR3_DMAT);
-
-	dma_mbuf_refresh(&usart2_tx_buffer);
-}
-
-void hdr_usart3(void)
-{
-	//disable the interrupt. It will be reenabled on a write if needed
-	nvic_clear_pending(NVIC_IRQ_USART3);
-	nvic_disable(NVIC_IRQ_USART3);
-	reg_reset(usart3->CR1, USART_CR1_TXEIE);
-	reg_set(usart3->CR3, USART_CR3_DMAT);
-
-	dma_mbuf_refresh(&usart3_tx_buffer);
-}
-

drv/usart.h

@@ -17,12 +17,19 @@
 
 //--type definitions------------------------------------------------------------
 
+/**
+ * Available USART peripherals. Note that some of these peripherals may not be
+ * available on all chips
+ */
 enum UsartPeriph {
 	USART_PERIPH_1,
 	USART_PERIPH_2,
 	USART_PERIPH_3,
 };
 
+/**
+ * Available configuration options
+ */
 enum UsartConfig {
 	USART_CONFIG_7E1,
 	USART_CONFIG_7E2,
@@ -39,20 +46,65 @@ enum UsartConfig {
 
 //--functions-------------------------------------------------------------------
 
+/**
+ * Configures the given USART peripheral using the provided condiguration
+ * options and baudrate. The baudrate may be any value supported by the
+ * peripheral, though some may not be exact due to precision errors (see
+ * table 192 in documentation). The baudrate is dependant on the peripheral's
+ * clock and changes to the later after this function has been called will cause
+ * the effective baudrate to change
+ *
+ * This function doesn't configure the required ports. This should be done using
+ * the gpio driver:
+ * - Tx port should be using GPIO_CONFIG_OUT_ALT_PUSH_PULL with
+ * the appropriate output speed based on the baurate (see GpioMode)
+ * - Rx port should be using GPIO_CONFIG_IN_FLOATING in input mode
+ * Both ports do not need to be configured if not used (e.g. if only using Tx,
+ * the Rx port can be left unconfigured)
+ */
 void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 		uint32_t baudrate);
 
+/**
+ * Resets the given USART peripheral, applying the default configuration and
+ * disabling it
+ */
 void usart_reset(enum UsartPeriph periph);
 
-uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte);
-
+/**
+ * Reads a single byte to the given USART peripheral, returning 0 if
+ * successfull, 1 otherwise.
+ *
+ * The Rx port must be configured for this function to ever return successfully
+ */
 uint32_t usart_read_byte(enum UsartPeriph periph, uint8_t* byte);
 
-void usart_set_tx_buffer(enum UsartPeriph periph, uint8_t** buffers,
-		uint16_t buffer_size, uint8_t buffer_nb, enum DmaConfig priority);
+/**
+ * Writes a single byte to the given USART peripheral, returning 0 if
+ * successfull, 1 otherwise.
+ *
+ * The Tx port must be configured for this function to do anything, though the
+ * function would still return 0
+ */
+uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte);
 
-void usart_set_rx_buffer(enum UsartPeriph periph, uint8_t* buffer,
-		uint16_t size, enum DmaConfig priority);
+/**
+ * Configures the given USART peripheral for DMA Rx operations, returning the
+ * corresponding DMA parameters to be used.
+ *
+ * The DMA must be configured separately using the DMA driver or an existing
+ * service
+ */
+const struct DmaParam* usart_configure_rx_dma(enum UsartPeriph periph);
+
+/**
+ * Configures the given USART peripheral for DMA Rx operations, returning the
+ * corresponding DMA parameters to be used.
+ *
+ * The DMA must be configured separately using the DMA driver or an existing
+ * service
+ */
+const struct DmaParam* usart_configure_tx_dma(enum UsartPeriph periph);
 
 
 #endif //_USART_H_

srv/dma_cbuf.c

@@ -12,9 +12,13 @@
 
 //--local definitions-----------------------------------------------------------
 
+/**
+ * DMA configuration to be used for the buffer. Additionnal configuration may be
+ * added by the peripherals used
+ */
 #define DMA_CONFIG (DMA_CONFIG_IRQ_COMPLETE | DMA_CONFIG_FROM_PERIPH  \
 					| DMA_CONFIG_CIRCULAR | DMA_CONFIG_INC_MEM        \
-					| DMA_CONFIG_PSIZE_8BITS | DMA_CONFIG_MSIZE_8BITS)
+					| DMA_CONFIG_MSIZE_8BITS)
 
 static void cbuf_callback(enum DmaIRQSource src, volatile void* param);
 
@@ -24,25 +28,25 @@ static void cbuf_callback(enum DmaIRQSource src, volatile void* param);
 //--public functions------------------------------------------------------------
 
 void dma_cbuf_configure(volatile struct DmaCircBuffer* buffer,
-		volatile void* raw_buffer, volatile void* src, uint16_t buffer_size,
-		enum DmaPeriph dma, enum DmaChannel channel, enum DmaConfig priority)
+		const struct DmaParam* param, enum DmaConfig priority,
+		volatile void* raw_buffer, uint16_t buffer_size)
 {
 	#warning "check for null ptr"
 
 	buffer->buffer = raw_buffer;
-	buffer->src = src;
 
 	buffer->size = buffer_size;
 	buffer->begin = 0;
 
-	buffer->dma = dma;
-	buffer->channel = channel;
-	buffer->config = DMA_CONFIG | priority;
+	buffer->dma = param->dma;
+	buffer->channel = param->channel;
 
 	buffer->dma_looped = false;
 
-	dma_configure(buffer->dma, buffer->channel, buffer->config, buffer->src,
-			buffer->buffer, buffer->size, cbuf_callback, buffer);
+	dma_configure(buffer->dma, buffer->channel,
+			DMA_CONFIG | param->config | priority,
+			param->periph, cbuf_callback, buffer);
+	dma_start(buffer->dma, buffer->channel, buffer->buffer, buffer->size);
 }
 
 uint32_t dma_cbuf_read_byte(volatile struct DmaCircBuffer* buffer,
@@ -86,4 +90,3 @@ static void cbuf_callback(enum DmaIRQSource src, volatile void* param)
 	buffer->dma_looped = true;
 }
 
-

srv/dma_cbuf.h

@@ -10,7 +10,7 @@
 
 //--includes--------------------------------------------------------------------
 
-#include "dma.h"
+#include "../drv/dma.h"
 
 
 //--type definitions------------------------------------------------------------
@@ -22,14 +22,12 @@
  */
 struct DmaCircBuffer {
 	volatile void* buffer;    //the buffer to use as a circular buffer
-	volatile void* src;       //source peripheral register
 
 	uint16_t size;            //the size of the buffer
 	uint16_t begin;           //pointer to the current begin of the buffer
 
-	enum DmaPeriph dma;       //DMA peripheral, must correspond to peripheral
-	enum DmaChannel channel;  //DMA channel, must correspond to peripheral
-	enum DmaConfig config;    //DMA config, must correspond to peripheral
+	enum DmaPeriph dma;      //DMA peripheral used for transfers
+	enum DmaChannel channel; //DMA channel used for transfers
 
 	bool dma_looped;          //whether the DMA looped or not (buffer overflow)
 };
@@ -40,16 +38,24 @@ struct DmaCircBuffer {
 /**
  * Configure a DMA circular buffer for a single DMA channel. A standard buffer
  * is used a base to construct a circular buffer, supplied in data by DMA
- * tranfers from a peripheral. The DMA's priority is given as parameters.
+ * tranfers from a peripheral.
  * The peripheral's specific configuration must be handled separately.
+ * Each peripheral's driver is responsible for providing the DMA configuration
+ * for said peripheral, though it can be manually given too. Please note that
+ * multiple peripherals may share the same DMA channel, which will cause issue
+ * when used with this buffer.
  *
  * Once this function is called, the system will start running right away and
  * will stay running until manually stopped
  */
 void dma_cbuf_configure(volatile struct DmaCircBuffer* buffer,
-		volatile void* raw_buffer, volatile void* src, uint16_t buffer_size,
-		enum DmaPeriph dma, enum DmaChannel channel, enum DmaConfig priority);
+		const struct DmaParam* param, enum DmaConfig priority,
+		volatile void* raw_buffer, uint16_t buffer_size);
 
+/**
+ * Reads a bytes from the buffer, returning if the read operation was
+ * successfull, 1 otherwise. This function is non-blocking.
+ */
 uint32_t dma_cbuf_read_byte(volatile struct DmaCircBuffer* buffer,
 		uint8_t* byte);
 

srv/dma_mbuf.c

@@ -0,0 +1,107 @@
+/** @file dma_mbuf.h
+ * Module handling Direct Memory Access controller's multibuffer system
+ *
+ * The module provides a convenient tool to send data to a peripheral in a
+ * buffered, low-altency, low-cpu usage, non-blocking way
+ */
+
+//--includes--------------------------------------------------------------------
+
+#include "dma_mbuf.h"
+
+
+//--local definitions-----------------------------------------------------------
+
+/**
+ * DMA configuration to be used for the buffer. Additionnal configuration may be
+ * added by the peripherals used
+ */
+#define DMA_CONFIG (DMA_CONFIG_IRQ_COMPLETE | DMA_CONFIG_FROM_MEM \
+					| DMA_CONFIG_INC_MEM | DMA_CONFIG_MSIZE_8BITS)
+
+static void mbuf_callback(enum DmaIRQSource src, volatile void* param);
+
+
+//--local variables-------------------------------------------------------------
+
+//--public functions------------------------------------------------------------
+
+void dma_mbuf_configure(volatile struct DmaMultiBuffer* buffer,
+		const struct DmaParam* param, enum DmaConfig priority,
+		void* raw_buffer, uint16_t buffer_size)
+{
+	#warning "check for null ptr"
+
+	buffer->raw_buffer = raw_buffer;
+
+	buffer->buffer_size = buffer_size / 2;
+
+	buffer->byte_index = 0;
+	buffer->buffer_index = 0;
+	buffer->dma = param->dma;
+	buffer->channel = param->channel;
+
+	buffer->dma_running = false;
+
+	dma_configure(buffer->dma, buffer->channel,
+			DMA_CONFIG | param->config | priority,
+			param->periph, mbuf_callback, buffer);
+}
+
+uint32_t dma_mbuf_write_byte(volatile struct DmaMultiBuffer* buffer,
+		uint8_t byte)
+{
+	//if the current buffer is full, give up
+	if (buffer->byte_index >= buffer->buffer_size) {
+		return 1;
+	}
+
+	//write the byte
+	buffer->raw_buffer[buffer->buffer_index * buffer->buffer_size
+		+ buffer->byte_index] = byte;
+	++buffer->byte_index;
+	return 0;
+}
+
+uint32_t dma_mbuf_switch(volatile struct DmaMultiBuffer* buffer)
+{
+	//no data to send, stop here
+	if (buffer->byte_index == 0) {
+		return 0;
+	}
+
+	//dma already running, give up
+	if (buffer->dma_running) {
+		return 1;
+	}
+
+	//start a new transfer
+	buffer->dma_running = true;
+	dma_start(buffer->dma, buffer->channel,
+			&buffer->raw_buffer[buffer->buffer_index * buffer->buffer_size],
+			buffer->byte_index);
+
+	buffer->byte_index = 0;
+	++buffer->buffer_index;
+	if (buffer->buffer_index > 1) {
+		buffer->buffer_index = 0;
+	}
+
+	return 0;
+}
+
+
+//--local functions-------------------------------------------------------------
+
+/**
+ * Callback called on DMA TX tranfert's completion. Stops the DMA and notifies
+ * the buffer that the transfer is done.
+ */
+static void mbuf_callback(enum DmaIRQSource src, volatile void* param)
+{
+	(void)src; //only transfer complete expected
+	volatile struct DmaMultiBuffer* buffer = param;
+	dma_stop(buffer->dma, buffer->channel);
+	buffer->dma_running = false;
+}
+

srv/dma_mbuf.h

@@ -0,0 +1,76 @@
+/** @file dma_mbuf.h
+ * Module handling Direct Memory Access controller's multibuffer system
+ *
+ * The module provides a convenient tool to send data to a peripheral in a
+ * buffered, low-latency, low-cpu usage, non-blocking way
+ */
+
+#ifndef _DMA_MBUF_H_
+#define _DMA_MBUF_H_
+
+//--includes--------------------------------------------------------------------
+
+#include "../drv/dma.h"
+
+
+//--type definitions------------------------------------------------------------
+
+/**
+ * Struct used by the multibuffer system. This system allows bufferized writes
+ * to a peripheral with controlled latency, minimal cpu usage and customisable
+ * buffer size
+ */
+struct DmaMultiBuffer {
+	uint8_t* raw_buffer;     //the buffer to use as a multi-buffer
+
+	uint16_t buffer_size;    //the size of the buffer
+
+	uint8_t byte_index;      //index of the next byte to be written
+	uint8_t buffer_index;    //index of the buffer being written to
+	enum DmaPeriph dma;      //DMA peripheral used for transfers
+	enum DmaChannel channel; //DMA channel used for transfers
+
+	bool dma_running;        //whether the dam is currently running or not
+};
+
+
+//--functions-------------------------------------------------------------------
+
+/**
+ * Configure a DMA multibuffer for a single DMA channel. The given buffer is
+ * divided into 2 to allow one part to be written to while the other is being
+ * transfered by the DMA to a peripheral.
+ * The peripheral's specific configuration must be handled separately.
+ * Each peripheral's driver is responsible for providing the DMA configuration
+ * for said peripheral, though it can be manually given too. Please note that
+ * multiple peripherals may share the same DMA channel, which will cause issue
+ * when used with this buffer.
+ *
+ * This buffer can be written to at any given time using dma_mbuf_write_byte(),
+ * but its content are only written to the corresponding peripheral when
+ * dma_mbuf_switch() is called.
+ */
+void dma_mbuf_configure(volatile struct DmaMultiBuffer* buffer,
+		const struct DmaParam* param, enum DmaConfig priority,
+		void* raw_buffer, uint16_t buffer_size);
+
+/**
+ * Write the given byte to the given buffer. Returns 0 if the write operation
+ * was successfull, 1 otherwise. The function is non-blocking.
+ *
+ * Note: calling this function will not trigger a DMA transfer, see
+ * dma_mbuf_switch() to do that
+ */
+uint32_t dma_mbuf_write_byte(volatile struct DmaMultiBuffer* buffer,
+		uint8_t byte);
+
+/**
+ * Switch the buffers, triggering a DMA transfer while allowing writes to
+ * continue. This function may fail if a DMA transfer is already running,
+ * returning 1
+ */
+uint32_t dma_mbuf_switch(volatile struct DmaMultiBuffer* buffer);
+
+
+#endif //_DMA_MBUF_H_
+

startup.s

@@ -4,7 +4,7 @@
  * This startup file provides a reset handler to setup the basics for c to run
  * (stack pointer, static data, ...) as well as the vector table and the
  * differents interrupt handlers that go with it. By default, all handlers use
- * the default handler wich is simply and infinite loop
+ * the default handler wich is simply an infinite loop
  */
 
 	.syntax unified
@@ -25,7 +25,7 @@
  */
 	.section .text.hdr_reset
 	.weak hdr_reset
-  	.type hdr_reset, %function
+	.type hdr_reset, %function
 hdr_reset:
 	ldr r0, = _estack
 	mov sp, r0