/* UART0-UART1 pass-through for ESP8266 Console
 *
 * ESP8266 socket header is connected to UART1.
 * Pin 2 - Tx (PB1)
 * Pin 3 - Rx (PB0)
 * UART0 is connected to the virtual COM port.
 * Both UART0 and UART1 are configured for 115200 Baud 8-N-1.
 * Use a terminal emulator to talk to UART0 through the virtual COM port.
 * If everything works out, type "AT<cr>" at the terminal emulator
 * should get "OK" back from ESP8266.
 *
 * The ESP8266 module must have the "AT" firmware. ESP8266 may have
 * different Baud rate than 115200 used in this program. 
 *
 * Built and tested with Keil MDK-ARM v5.24a and TM4C_DFP v1.1.0
 */

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

void UART0Tx(char c);
unsigned char UART0Rx(void);
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 = 27;       /* 50MHz/16=3.125MHz, 3.125MHz/115200=27.1267 */
    UART1->FBRD = 8;        /* fraction part, 0.1267*64=8 */
    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 TX and RX 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 */
    
    SYSCTL->RCGCUART |= 1;  /* provide clock to UART0 */
    SYSCTL->RCGCGPIO |= 1;  /* enable clock to PORTA */

    /* UART0 initialization */
    UART0->CTL = 0;         /* disable UART0 */
    UART0->IBRD = 27;       /* 50MHz/16=3.125MHz, 3.125MHz/115200=27.1267 */
    UART0->FBRD = 8;        /* fraction part, 0.1267*64=8 */
    UART0->CC = 0;          /* use system clock */
    UART0->LCRH = 0x60;     /* 8-bit, no parity, 1-stop bit, no FIFO */
    UART0->CTL = 0x301;     /* enable UART0, TXE, RXE */

    // UART0 TX and RX use PA0 and PA1. Set them up.
    GPIOA->DEN = 0x03;      /* Make PA0 and PA1 as digital */
    GPIOA->AFSEL = 0x03;    /* Use PA0, PA1 alternate function */
    GPIOA->PCTL = 0x11;     /* configure PA0 and PA1 for UART */

    delayMs(1);             /* wait for output line to stabilize */

    UART0Tx('>');           /* send prompt to console */
    
    for(;;) {
        c = UART0Rx();
        if (c != 0)
            UART1Tx(c); 

        c = UART1Rx();
        if (c != 0)
            UART0Tx(c); 
    }
}

void UART1Tx(char c) {
    while((UART1->FR & 0x20) != 0); /* wait until Tx buffer not full */
    UART1->DR = c;                  /* before giving it another byte */
}

/* non-blocking read. returns 0 if no char available */
unsigned char UART1Rx(void){
    char c;
    if ((UART1->FR & 0x10) != 0)    /* if RSx buffer is empty */
        return 0;                   /* return 0 */
    c = UART1->DR;                  /* read the received data */
    return c;                       /* and return it */
}

void UART0Tx(char c) {
    while((UART0->FR & 0x20) != 0); /* wait until Tx buffer not full */
    UART0->DR = c;                  /* before giving it another byte */
}

/* non-blocking read. returns 0 if no char available */
unsigned char UART0Rx(void){
    char c;
    if ((UART0->FR & 0x10) != 0)    /* if Rx buffer is empty */
        return 0;                   /* return 0 */
    c = UART0->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 */
}