diff --git a/drv/usart.c b/drv/usart.c
index 35bc779..25167a2 100644
--- a/drv/usart.c
+++ b/drv/usart.c
@@ -29,50 +29,52 @@ static void configure_baudrate(volatile struct USART* regs, uint32_t clock,
 
 //--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 const struct DmaParam usart1_rx_param = {
-	(void*)&usart1->DR,
-	DMA_CONFIG,
-	DMA_PERIPH_1,
-	DMA_CHANNEL_5,
+static volatile struct USART* const usarts[] = {
+	(struct USART*)USART1_BASE_ADDRESS,
+	(struct USART*)USART2_BASE_ADDRESS,
+	(struct USART*)USART3_BASE_ADDRESS,
 };
 
-static const struct DmaParam usart2_rx_param = {
-	(void*)&usart2->DR,
-	DMA_CONFIG,
-	DMA_PERIPH_1,
-	DMA_CHANNEL_6,
+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 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,
+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,
+	},
 };
 
 
@@ -87,18 +89,21 @@ 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);
+			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);
+			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);
+			configure_baudrate(usarts[USART_PERIPH_3], clocks.apb1_freq,
+					baudrate);
+			configure_usart(usarts[USART_PERIPH_3], config);
 			break;
 		default:
 			break;
@@ -107,25 +112,12 @@ void usart_configure(enum UsartPeriph periph, enum UsartConfig config,
 
 uint32_t usart_read_byte(enum UsartPeriph periph, uint8_t* byte)
 {
-	volatile struct USART* regs;
-
-	switch (periph) {
-		case USART_PERIPH_1:
-			regs = usart1;
-			break;
-		case USART_PERIPH_2:
-			regs = usart2;
-			break;
-		case USART_PERIPH_3:
-			regs = usart3;
-			break;
-		default:
-			return 1;
-			break;
+	if (periph > USART_PERIPH_3) {
+		return 1;
 	}
 
-	if (regs->SR.RXNE) {
-		*byte = regs->DR.DR;
+	if (usarts[periph]->SR.RXNE) {
+		*byte = usarts[periph]->DR.DR;
 		return 0;
 	} else {
 		return 1;
@@ -134,26 +126,13 @@ uint32_t usart_read_byte(enum UsartPeriph periph, uint8_t* byte)
 
 uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte)
 {
-	volatile struct USART* regs;
-
-	switch (periph) {
-		case USART_PERIPH_1:
-			regs = usart1;
-			break;
-		case USART_PERIPH_2:
-			regs = usart2;
-			break;
-		case USART_PERIPH_3:
-			regs = usart3;
-			break;
-		default:
-			return 1;
-			break;
+	if (periph > USART_PERIPH_3) {
+		return 1;
 	}
 
 	//only write data if the tx register it empty, give up otherwise
-	if (regs->SR.TXE) {
-		reg_write(regs->DR, USART_DR_DR, byte);
+	if (usarts[periph]->SR.TXE) {
+		reg_write(usarts[periph]->DR, USART_DR_DR, byte);
 		return 0;
 	} else {
 		return 1;
@@ -162,50 +141,22 @@ uint32_t usart_write_byte(enum UsartPeriph periph, uint8_t byte)
 
 const struct DmaParam* usart_configure_rx_dma(enum UsartPeriph periph)
 {
-	const struct DmaParam* param;
-
-	switch (periph) {
-		case USART_PERIPH_1:
-			param = &usart1_rx_param;
-			reg_set(usart1->CR3, USART_CR3_DMAR);
-			break;
-		case USART_PERIPH_2:
-			param = &usart2_rx_param;
-			reg_set(usart2->CR3, USART_CR3_DMAR);
-			break;
-		case USART_PERIPH_3:
-			param = &usart3_rx_param;
-			reg_set(usart3->CR3, USART_CR3_DMAR);
-			break;
-		default:
-			return nullptr;
+	if (periph > USART_PERIPH_3) {
+		return nullptr;
 	}
 
-	return param;
+	reg_set(usarts[periph]->CR3, USART_CR3_DMAR);
+	return &usarts_rx_param[periph];
 }
 
 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;
+	if (periph > USART_PERIPH_3) {
+		return nullptr;
 	}
 
-	return param;
+	reg_set(usarts[periph]->CR3, USART_CR3_DMAT);
+	return &usarts_tx_param[periph];
 }