/* UART1 echo
 *
 * Pin header J34 is connected to UART1.
 * Pin 2 - Tx (PB1)
 * Pin 3 - Rx (PB0)
 * The UART1 is configure for 9600 Baud 8-N-1.
 * Connect a USB to 3.3V serial converter to a PC and launch a
 * terminal emulator on the PC. The keyboard input will be sent
 * by the terminal emulator to USB-serial converter. Connect the
 * Tx pin of the converter to the Rx (pin 3 of J34). This program
 * echoes back the characters to the Tx (pin 2 of J34). Connect Tx
 * of J34 to Rx of the USB-Serial converter and the character will
 * appear on the terminal emulator window.
 *
 * Built and tested with Keil MDK-ARM v5.24a and TM4C_DFP v1.1.0
 */

#include <stdint.h>
#include "TM4C123.h"

void UART1Tx(char c);
unsigned char UART1Rx(void);
void delayMs(int n);

int main(void) {
    char c;
    
    SYSCTL->RCGCUART |= 2;  /* provide clock to UART1 */
    SYSCTL->RCGCGPIO |= 2;  /* enable clock to PORTB */
    
    /* UART1 initialization */
    UART1->CTL = 0;         /* disable UART1 */
    UART1->IBRD = 325;      /* 50MHz/16=3.125MHz, 3.125MHz/325=9600 baud rate */
    UART1->FBRD = 33;       /* fraction part, see Example 4-4 */
    UART1->CC = 0;          /* use system clock */
    UART1->LCRH = 0x60;     /* 8-bit, no parity, 1-stop bit, no FIFO */
    UART1->CTL = 0x301;     /* enable UART1, TXE, RXE */

    /* UART1 TX0 and RX0 use PB1 and PB0. Set them up. */
    GPIOB->DEN = 0x03;      /* Make PB0 and PB1 as digital */
    GPIOB->AFSEL = 0x03;    /* Use PB0,PB1 alternate function */
    GPIOB->PCTL = 0x11;     /* configure PB0 and PB1 for UART */
    
    delayMs(1);             /* wait for output line to stabilize */

    UART1Tx('>');
    
    for(;;) {
        c = UART1Rx();
        if (c == '\r')
            UART1Tx('\n'); 
        UART1Tx(c); 
    }
}

/* UART1 Transmit
 * This function waits until the transmit buffer is available then
 * write the character in the transmit buffer.  It does not wait
 * for transmission to complete.
 */
void UART1Tx(char c) {
    while((UART1->FR & 0x20) != 0); /* wait until Tx buffer not full */
    UART1->DR = c;                  /* before giving it another byte */
}


unsigned char UART1Rx(void){
    char c;
    while((UART1->FR & 0x10) != 0); // wait until the buffer is not empty
    c = UART1->DR;                  // read the received data
    return c;                       // and return it
}


/* delay n milliseconds (50 MHz CPU clock) */
void delayMs(int n) {
    int i, j;
    for(i = 0 ; i< n; i++)
        for(j = 0; j < 6265; j++)
            {}  /* do nothing for 1 ms */
}