0x0001_hello-world code

0x0001_hello-world/.vscode/settings.json

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+{
+    "files.associations": {
+        "stm32f4xx.h": "c"
+    }
+}

0x0001_hello-world/include/usart.h

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+/**
+ * FILE: usart.h
+ *
+ * DESCRIPTION: This file contains the usart function definitions utilizing the STM32F401CC6 microcontroller.
+ *
+ * AUTHOR: Kevin Thomas
+ * DATE: October 6, 2023
+ */
+
+#ifndef USART_H
+#define USART_H
+
+#include <stdint.h>
+
+#include "stm32f4xx.h"
+
+#define DEFAULT_CLK_SPEED 16000000U
+
+extern int __io_putchar(int ch) __attribute__((weak));
+
+/**
+ * @brief  Sets the baud rate for a given USART peripheral.
+ *
+ *         This function calculates and sets the baud rate register (BRR) for
+ *         the specified USART peripheral based on the provided peripheral clock
+ *         speed and desired baud rate.
+ *
+ * @param  USARTx: Pointer to the USART peripheral (e.g., USART1, USART2, etc.).
+ * @param  periph_clk: The frequency of the peripheral clock in Hertz.
+ * @param  baud_rate: The desired baud rate for communication.
+ * @retval None
+ */
+static void set_baud_rate(USART_TypeDef *USARTx,  uint32_t periph_clk, uint32_t baud_rate);
+
+/**
+ * @brief  Initializes USART2 for transmission on PA2 pin.
+ *
+ *         This function configures the necessary settings for USART2 to enable
+ *         transmission on pin PA2. It includes configuring GPIO, setting
+ *         alternate function mode, configuring the USART clock, setting the
+ *         baud rate, and enabling the transmitter.
+ *
+ * @param  None
+ * @retval None
+ */
+void usart2_tx_init(void);
+
+/**
+ * @brief  Writes a single byte to USART2 for transmission.
+ *
+ *         This function writes a single byte to the USART2 transmit data
+ *         register for transmission. It ensures that the transmit data register
+ *         is empty before writing the byte.
+ *
+ * @param  ch: The byte to be transmitted.
+ * @retval None
+ */
+void usart2_write(uint8_t ch);
+
+#endif // USART_H

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

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+/**
+ * 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);
+}