physical.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>

#include "physical.h"

// Open /dev/mem to give access to physical addresses
int open_physical(int fd) {
    if (fd == -1) {
        // check if already open
        if ((fd = open("/dev/mem", (O_RDWR | O_SYNC))) == -1) {
            printf("ERROR: could not open \"/dev/mem\"...\n");
            return -1;
        }
    }
    return fd;
}

// Close /dev/mem to give access to physical addresses
void close_physical(int fd) {
    close(fd);
}

// Establish a virtual address mapping for the physical addresses
// starting at base and extending by span bytes
void * map_physical(int fd, unsigned int base, unsigned int span) {
    void * virtual_base;
    // Get a mapping from physical addresses to virtual addresses
    virtual_base = mmap(NULL, span, (PROT_READ | PROT_WRITE), MAP_SHARED, fd, base);
    if (virtual_base == MAP_FAILED) {
        printf("ERROR: mmap() failed...\n");
        close(fd);
        return NULL;
    }
    return virtual_base;
}

// Close the previously-opened virtual address mapping
int unmap_physical(void * virtual_base, unsigned int span) {
    if (munmap (virtual_base, span) != 0) {
        printf("ERROR: munmap() failed...\n");
        return -1;
    }
    return 0;
}