Rework DMA buffer to work properly

DMA buffers now work reliably with USART. The DMA api has changed to make it
more efficient code-size-wise. This may, however, complicate things when
implementating powersaving features

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;
@@ -110,20 +110,21 @@ void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel)
 	}
 }
 
-void dma_enable(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:
-			reg_set(dma1->CHANNELS[channel].CCR, DMA_CCR_EN);
 			if (dma1_callbacks[channel]) {
 				nvic_enable(NVIC_IRQ_DMA1_CHANNEL1 + channel);
 			}
+			start_dma(dma1, channel, mem, size);
 			break;
 		case DMA_PERIPH_2:
-			reg_set(dma2->CHANNELS[channel].CCR, DMA_CCR_EN);
 			if (dma2_callbacks[channel]) {
 				nvic_enable(NVIC_IRQ_DMA2_CHANNEL1 + channel);
 			}
+			start_dma(dma2, channel, mem, size);
 			break;
 		default:
 			return;
@@ -146,7 +147,7 @@ void dma_enter_critical(enum DmaPeriph dma, enum DmaChannel channel)
 	}
 }
 
-void dma_disable(enum DmaPeriph dma, enum DmaChannel channel)
+void dma_stop(enum DmaPeriph dma, enum DmaChannel channel)
 {
 	switch (dma) {
 		case DMA_PERIPH_1:
@@ -185,21 +186,27 @@ uint16_t dma_get_remaining(enum DmaPeriph dma, enum DmaChannel channel)
 //--local functions-------------------------------------------------------------
 
 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);
 }
 
+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

@@ -77,12 +77,19 @@ enum DmaIRQSource {
 
 typedef void (*DmaCallback)(enum DmaIRQSource, volatile void* param);
 
+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-------------------------------------------------------------------
 
 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);
 
 void dma_configure_mem2mem(enum DmaPeriph dma, enum DmaChannel channel,
 		enum DmaConfigM2M config_mask, const void* src, void* dest,
@@ -92,11 +99,12 @@ void dma_reset(enum DmaPeriph dma, enum DmaChannel channel);
 
 void dma_exit_critical(enum DmaPeriph dma, enum DmaChannel channel);
 
-void dma_enable(enum DmaPeriph dma, enum DmaChannel channel);
+void dma_start(enum DmaPeriph dma, enum DmaChannel channel,
+		volatile void* mem, uint16_t size);
 
 void dma_enter_critical(enum DmaPeriph dma, enum DmaChannel channel);
 
-void dma_disable(enum DmaPeriph dma, enum DmaChannel channel);
+void dma_stop(enum DmaPeriph dma, enum DmaChannel channel);
 
 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/usart.c

@@ -14,8 +14,6 @@
 
 #include "rcc.h"
 #include "dma.h"
-#include "dma_mbuf.h"
-#include "dma_cbuf.h"
 
 #include "stddef.h"
 
@@ -27,6 +25,8 @@ 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-------------------------------------------------------------
 
@@ -34,12 +34,47 @@ 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 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 usart1_rx_param = {
+	(void*)&usart1->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_5,
+};
+
+static const struct DmaParam usart2_rx_param = {
+	(void*)&usart2->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_6,
+};
+
+static const struct DmaParam usart3_rx_param = {
+	(void*)&usart3->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_3,
+};
+
+static const struct DmaParam usart1_tx_param = {
+	(void*)&usart1->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_4,
+};
+
+static const struct DmaParam usart2_tx_param = {
+	(void*)&usart2->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_7,
+};
+
+static const struct DmaParam usart3_tx_param = {
+	(void*)&usart3->DR,
+	DMA_CONFIG,
+	DMA_PERIPH_1,
+	DMA_CHANNEL_2,
+};
 
 
 //--public functions------------------------------------------------------------
@@ -55,22 +90,16 @@ void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 			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;
 			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;
 			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;
 			break;
 		default:
 			break;
@@ -80,43 +109,22 @@ void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 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);
@@ -124,90 +132,84 @@ uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte)
 	} 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 (buffer->buffer) {
-		return dma_cbuf_read_byte(buffer, byte);
-	} else {
 	if (regs->SR.RXNE) {
 		*byte = regs->DR.DR;
 		return 0;
 	} else {
 		return 1;
 	}
-	}
 }
 
-void usart_set_tx_buffer(enum UsartPeriph periph, uint8_t** buffers,
-		uint16_t buffer_size, uint8_t buffer_nb, enum DmaConfig priority)
+const struct DmaParam* usart_configure_rx_dma(enum UsartPeriph periph)
 {
-	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;
-	}
-}
+	const struct DmaParam* param;
 
-void usart_set_rx_buffer(enum UsartPeriph periph, uint8_t* buffer,
-		uint16_t size, enum DmaConfig priority)
-{
 	switch (periph) {
 		case USART_PERIPH_1:
-			dma_cbuf_configure(&usart1_rx_buffer, buffer, (void*)&usart1->DR,
-					size, DMA_PERIPH_1, DMA_CHANNEL_5, priority);
+			param = &usart1_rx_param;
 			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);
+			param = &usart2_rx_param;
 			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);
+			param = &usart3_rx_param;
 			reg_set(usart3->CR3, USART_CR3_DMAR);
-
 			break;
+		default:
+			return nullptr;
 	}
+
+	return param;
 }
 
+const struct DmaParam* usart_configure_tx_dma(enum UsartPeriph periph)
+{
+	const struct DmaParam* param;
+
+	switch (periph) {
+		case USART_PERIPH_1:
+			param = &usart1_tx_param;
+			reg_set(usart1->CR3, USART_CR3_DMAT);
+			break;
+		case USART_PERIPH_2:
+			param = &usart2_tx_param;
+			reg_set(usart2->CR3, USART_CR3_DMAT);
+			break;
+		case USART_PERIPH_3:
+			param = &usart3_tx_param;
+			reg_set(usart3->CR3, USART_CR3_DMAT);
+			break;
+		default:
+			return nullptr;
+	}
+
+	return param;
+}
+
+
 //--local functions-------------------------------------------------------------
 
 /**
@@ -309,39 +311,3 @@ 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

@@ -41,18 +41,13 @@ enum UsartConfig {
 
 void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 		uint32_t baudrate);
-
 void usart_reset(enum UsartPeriph periph);
 
 uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte);
-
 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);
-
-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);
+const struct DmaParam* usart_configure_tx_dma(enum UsartPeriph periph);
 
 
 #endif //_USART_H_

srv/dma_cbuf.c

@@ -24,25 +24,25 @@ 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 +86,3 @@ 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;
+	enum DmaChannel channel;
 
 	bool dma_looped;          //whether the DMA looped or not (buffer overflow)
 };
@@ -47,8 +45,8 @@ struct DmaCircBuffer {
  * 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);
 
 uint32_t dma_cbuf_read_byte(volatile struct DmaCircBuffer* buffer,
 		uint8_t* byte);

srv/dma_mbuf.c

@@ -0,0 +1,100 @@
+/** @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);
+
+
+//--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;
+}
+
+void dma_mbuf_switch(volatile struct DmaMultiBuffer* buffer)
+{
+	//if transfer already in progress or no data to send, don't start the
+	//transfer
+	if (buffer->dma_running || buffer->byte_index == 0) {
+		return;
+	}
+
+	//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;
+}
+
+
+//--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;
+	dma_stop(buffer->dma, buffer->channel);
+	buffer->dma_running = false;
+}
+

srv/dma_mbuf.h

@@ -10,7 +10,7 @@
 
 //--includes--------------------------------------------------------------------
 
-#include "dma.h"
+#include "../drv/dma.h"
 
 
 //--type definitions------------------------------------------------------------
@@ -21,19 +21,16 @@
  * sizes
  */
 struct DmaMultiBuffer {
-	void** buffers;           //list of buffers to write to
-	volatile void* dest;      //destination peripheral register
+	uint8_t* raw_buffer;
 
-	uint16_t buffer_size;     //size of a single buffer
+	uint16_t buffer_size;
 
-	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
+	uint8_t byte_index;
+	uint8_t buffer_index;
+	enum DmaPeriph dma;
+	enum DmaChannel channel;
 
-	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
+	bool dma_running;
 };
 
 
@@ -51,9 +48,9 @@ struct DmaMultiBuffer {
  * 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);
+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
@@ -71,7 +68,7 @@ uint32_t dma_mbuf_write_byte(volatile struct DmaMultiBuffer* buffer,
  * transfer will be handled automatically until there are no bytes left in the
  * buffer
  */
-void dma_mbuf_refresh(volatile struct DmaMultiBuffer* buffer);
+void 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
@@ -75,19 +75,19 @@ bss_init_end:
  */
 	.section .text.hdr_default, "ax", %progbits
 	.weak hdr_default
-hdr_default:
+	hdr_default:
 	b hdr_default
 
 	.size hdr_default, .-hdr_default
 
 
-//--Vector table----------------------------------------------------------------
+	//--Vector table----------------------------------------------------------------
 
 	.section .vector_table, "a", %progbits
 	.type vector_table, %object
 	.size vector_table, .-vector_table
 
-vector_table:
+	vector_table:
 	.word _estack
 	.word hdr_reset
 	.word hdr_nmi
@@ -165,7 +165,7 @@ vector_table:
 	.word hdr_dma2_channel3
 	.word hdr_dma2_channel4_5
 
-//--Weak definitions------------------------------------------------------------
+	//--Weak definitions------------------------------------------------------------
 
 	.weak hdr_nmi
 	.thumb_set hdr_nmi, hdr_default