/* p4_3.c Send a string "Hello\r\n" to USART1
 *
 * USART1 Tx signal is connected to pin PA9. To see the output of USART1
 * on a PC, you need to use a USB-serial module. Connect the Rx pin of
 * the module to the PA9 pin of the STM32F030 Nucleo board. Make sure
 * the USB-serial module you use has a 3.3V interface.
 *
 * By default, the clock is running at 8 MHz.
 * The UART1 is configured for 9600 Baud.
 * PA9 - USART1 TX (AF1)
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */
#include "stm32F0xx.h"

void USART1_init(void);
void USART1_write(int c);
void delayMs(int);

/*----------------------------------------------------------------------------
  MAIN function
 *----------------------------------------------------------------------------*/
int main (void) {
    char message[] = "Hello\r\n";
    int i;

    USART1_init();

    while (1) {
        for (i = 0; i < 7; i++) {
            USART1_write(message[i]); /* send a char */
        }
        delayMs(500);                /* leave a gap between messages */
    }
}

/*----------------------------------------------------------------------------
  Initialize USART pins, Baudrate
 *----------------------------------------------------------------------------*/
void USART1_init (void) {
    RCC->AHBENR |= RCC_AHBENR_GPIOAEN;          /* Enable GPIOA clock */
    RCC->APB2ENR |= RCC_APB2ENR_USART1EN;    /* Enable USART1 clock */

    /* Configure PA9 for USART1_TX */
    GPIOA->AFR[1] &= ~0x00F0;
    GPIOA->AFR[1] |=  0x0010;   /* alt1 for USART1 */
    GPIOA->MODER  &= ~0xC0000;
    GPIOA->MODER  |=  0x80000;   /* enable alternate function for PA9 */

    USART1->BRR = 0x0341;       /* 9600 baud @ 8 MHz */
    USART1->CR1 = 0x0008;       /* enable Tx, 8-bit data */
    USART1->CR2 = 0x0000;       /* 1 stop bit */
    USART1->CR3 = 0x0000;       /* no flow control */
    USART1->CR1 |= 0x0001;      /* enable USART1 */
}


/* Write a character to USART1 */
void USART1_write (int ch) {
    while (!(USART1->ISR & USART_ISR_TXE)) {}   // wait until Tx buffer empty
    USART1->TDR = (ch & 0xFF);
}

void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 1597; i++) ;
}