rust-raspberrypi-OS-tutorials/14_raspbootin64/main.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 "uart.h"

// import our start address from linker
extern char _start;

void main()
{
    int size=0;
    char *kernel=(char*)&_start;

    // set up serial console
    uart_init();

    // say hello. To reduce loader size I removed uart_puts()
again:
    uart_send('R');
    uart_send('B');
    uart_send('I');
    uart_send('N');
    uart_send('6');
    uart_send('4');
    uart_send('\r');
    uart_send('\n');
    // notify raspbootcom to send the kernel
    uart_send(3);
    uart_send(3);
    uart_send(3);

    // read the kernel's size
    size=uart_getc();
    size|=uart_getc()<<8;
    size|=uart_getc()<<16;
    size|=uart_getc()<<24;

    // send negative or positive acknowledge
    if(size<64 || size>1024*1024) {
        // size error
        uart_send('S');
        uart_send('E');
        goto again;
    }
    uart_send('O');
    uart_send('K');

    // read the kernel
    while(size--) *kernel++ = uart_getc();

    // jump to the new kernel
    asm volatile ("b 0x80000");
}