raspi3-tutorial/14_raspbootin64/uart.c

/*
 * Copyright (C) 2018 bzt (bztsrc@github)
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 */

#include "gpio.h"
#include "mbox.h"

/* PL011 UART registers */
#define UART0_DR        ((volatile unsigned int*)(MMIO_BASE+0x00201000))
#define UART0_FR        ((volatile unsigned int*)(MMIO_BASE+0x00201018))
#define UART0_IBRD      ((volatile unsigned int*)(MMIO_BASE+0x00201024))
#define UART0_FBRD      ((volatile unsigned int*)(MMIO_BASE+0x00201028))
#define UART0_LCRH      ((volatile unsigned int*)(MMIO_BASE+0x0020102C))
#define UART0_CR        ((volatile unsigned int*)(MMIO_BASE+0x00201030))
#define UART0_IMSC      ((volatile unsigned int*)(MMIO_BASE+0x00201038))
#define UART0_ICR       ((volatile unsigned int*)(MMIO_BASE+0x00201044))

/**
 * Set baud rate and characteristics (115200 8N1) and map to GPIO
 */
void uart_init()
{
    register unsigned int r;

    /* initialize UART */
    *UART0_CR = 0;         // turn off UART0

    /* set up clock for consistent divisor values */
    mbox[0] = 9*4;
    mbox[1] = MBOX_REQUEST;
    mbox[2] = MBOX_TAG_SETCLKRATE; // set clock rate
    mbox[3] = 12;
    mbox[4] = 8;
    mbox[5] = 2;           // UART clock
    mbox[6] = 4000000;     // 4Mhz
    mbox[7] = 0;           // clear turbo
    mbox[8] = MBOX_TAG_LAST;
    mbox_call(MBOX_CH_PROP);

    /* map UART0 to GPIO pins */
    r=*GPFSEL1;
    r&=~((7<<12)|(7<<15)); // gpio14, gpio15
    r|=(4<<12)|(4<<15);    // alt0
    *GPFSEL1 = r;
    *GPPUD = 0;            // enable pins 14 and 15
    r=150; while(r--) { asm volatile("nop"); }
    *GPPUDCLK0 = (1<<14)|(1<<15);
    r=150; while(r--) { asm volatile("nop"); }
    *GPPUDCLK0 = 0;        // flush GPIO setup

    *UART0_ICR = 0x7FF;    // clear interrupts
    *UART0_IBRD = 2;       // 115200 baud
    *UART0_FBRD = 0xB;
    *UART0_LCRH = 0x7<<4;  // 8n1, enable FIFOs
    *UART0_CR = 0x301;     // enable Tx, Rx, UART
}

/**
 * Send a character
 */
void uart_send(unsigned int c) {
    /* wait until we can send */
    do{asm volatile("nop");}while(*UART0_FR&0x20);
    /* write the character to the buffer */
    *UART0_DR=c;
}

/**
 * Receive a character
 */
char uart_getc() {
    /* wait until something is in the buffer */
    do{asm volatile("nop");}while(*UART0_FR&0x10);
    /* read it and return */
    return (char)(*UART0_DR);
}