0x0001_hello-world code

0x0001_hello-world/src/main.c

@@ -1,6 +1,22 @@
+/**
+ * FILE: main.s
+ *
+ * DESCRIPTION: This file contains the main function for the hello-world program utilizing the STM32F401CC6 microcontroller.
+ *
+ * AUTHOR: Kevin Thomas
+ * DATE: October 6, 2023
+ */
+
 #include <stdio.h>
 
+#include "usart.h"
+
 int main(void)
 {
+    usart2_tx_init();
 
+    while (1)
+    {
+        printf("hello, world\r\n");
+    }
 }

0x0001_hello-world/src/usart.c

@@ -0,0 +1,75 @@
+/**
+ * FILE: usart.s
+ *
+ * DESCRIPTION: This file contains the usart functions utilizing the STM32F401CC6 microcontroller.
+ *
+ * AUTHOR: Kevin Thomas
+ * DATE: October 6, 2023
+ */
+
+
+#include "usart.h"
+
+__attribute__((weak)) int _write(int file, char *ptr, int len)
+{
+    (void)file;
+    int data_idx;
+
+    for (data_idx = 0; data_idx < len; data_idx++)
+    {
+        __io_putchar(*ptr++);
+    }
+
+    return len;
+}
+
+int __io_putchar(int ch)
+{
+    // write a single char
+    usart2_write(ch);
+
+    return ch;
+}
+
+static void set_baud_rate(USART_TypeDef *USARTx,  uint32_t periph_clk, uint32_t baud_rate)
+{
+    // set baud rate register
+    USARTx->BRR = ((periph_clk + (baud_rate / 2)) / baud_rate);
+}
+
+void usart2_tx_init(void)
+{
+    // enable GPIOA clock
+    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
+
+    // set PA2 to output alternate function mode
+    GPIOA->MODER |= GPIO_MODER_MODE2_1;
+    GPIOA->MODER &= ~GPIO_MODER_MODE2_0;
+
+    // set PA2 alternate function type to UART_TX (AF07)
+    GPIOA->AFR[0] &= ~GPIO_AFRL_AFRL2_3;
+    GPIOA->AFR[0] |= GPIO_AFRL_AFRL2_2;
+    GPIOA->AFR[0] |= GPIO_AFRL_AFRL2_1;
+    GPIOA->AFR[0] |= GPIO_AFRL_AFRL2_0;
+
+    // enable USART2 clock
+    RCC->APB1ENR |= RCC_APB1ENR_USART2EN;
+
+    // configure baud rate to 9600
+    set_baud_rate(USART2, DEFAULT_CLK_SPEED, 9600);
+
+    // configure TX transmitter enable
+    USART2->CR1 |= USART_CR1_TE;
+
+    // enable UART2
+    USART2->CR1 |= USART_CR1_UE;
+}
+
+void usart2_write(uint8_t ch)
+{
+    // verify transmit data register is empty, will return true if the bit is set
+    while(!(USART2->SR & USART_SR_TXE)) {};
+
+    // write a single char to the transmit data register
+    USART2->DR = (ch & 0xFF);
+}