mbox.c

/*
 * Copyright (C) 2022 (Unix69@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"


/**
 * Make a mailbox call. Returns 0 on failure, non-zero on success
 */
int mbox_call(unsigned char ch)
{
    unsigned int r = (((unsigned int)((unsigned long)&mbox)&~0xF) | (ch&0xF));
    /* wait until we can write to the mailbox */
    do{asm volatile("nop");}while(*MBOX_STATUS & MBOX_FULL);
    /* write the address of our message to the mailbox with channel identifier */
    *MBOX_WRITE = r;
    /* now wait for the response */
    while(1) {
        /* is there a response? */
        do{asm volatile("nop");}while(*MBOX_STATUS & MBOX_EMPTY);
        /* is it a response to our message? */
        if(r == *MBOX_READ)
            /* is it a valid successful response? */
            return mbox[1]==MBOX_RESPONSE;
    }
    return 0;
}