wip

src/main.c

@@ -80,7 +80,7 @@ int main(void) {
   (void) usart2_init();
 
   (void) tim4_start();
-  (void) tim4_start();
+  (void) usart2_start();
 
   uint16_t led = PIN('C', 13);           // Blue LED
   RCC->AHB1ENR |= BIT(PINPORT(led));     // Enable GPIO clock for LED
@@ -93,8 +93,7 @@ int main(void) {
 	 led_on = !led_on;
 	 gpio_write(led, led_on);
 
-while ((USART2->ISR & USART_ISR_TC) != USART_ISR_TC);
-				USART2->TDR = '#';
+	 usart2_write_byte('a');
 
 	 counter = TIM4->CNT;
 	}

src/usart.c

@@ -49,9 +49,9 @@ void usart2_init(void) {
   USART2->CR1 |= USART_CR1_OVER8_8;
 
   USART2->BRR &= ~(USART_BRR_MANTISSA_MASK << USART_BRR_MANTISSA_BIT);
-  USART2->BRR |= (52 << USART_BRR_MANTISSA_BIT);
+  USART2->BRR |= (0x34 << USART_BRR_MANTISSA_BIT);
   USART2->BRR &= ~(USART_BRR_FRACTION_MASK << USART_BRR_FRACTION_BIT);
-  USART2->BRR |= (0 << USART_BRR_FRACTION_BIT);
+  USART2->BRR |= (0x0 << USART_BRR_FRACTION_BIT);
 
   // Enable transmitter and receiver
   USART2->CR1 |= USART_CR1_TE_ENABLE;
@@ -61,3 +61,11 @@ void usart2_init(void) {
 void usart2_start(void) {
   USART2->CR1 |= USART_CR1_UE_ENABLE;
 }
+
+void usart2_write_byte(char c) {
+  // Send data
+  USART2->DR = c;
+
+  // Wait indefinitely for transmission to be ready for data
+  while ((USART2->SR & USART_SR_TXE_TRANSMITTED) == 0);
+}

src/usart.h

@@ -16,6 +16,15 @@ struct usart {
 #define USART2_BASE_ADDR (0x40004400U)
 #define USART2 ((struct usart *) USART2_BASE_ADDR)
 
+// SR Register
+// Transmission data register empty
+#define USART_SR_TXE_BIT 7
+#define USART_SR_TXE_TRANSMITTED (1 << USART_SR_TXE_BIT)
+
+// Read data register not empty
+#define USART_SR_RXNE_BIT 5
+#define USART_SR_RXNE_READY (1 <<USART_SR_RXNE_BIT)
+
 // CR Register
 // Oversampling mode
 #define USART_CR1_OVER8_BIT 15
@@ -43,4 +52,6 @@ struct usart {
 void usart2_init(void);
 void usart2_start(void);
 
+void usart2_write_byte(char byte);
+
 #endif