//-------------------------------------------------------------------
//	mmwhere.cpp
//
//	This program shows the extent to which an application can
//	control the location at which our '/dev/vram' device-file
//	will be memory-mapped by the standard 'mmap()' function.
//
//	NOTE: Written and tested with Linux kernel version 2.4.20.
//	
//	programmer: ALLAN CRUSE
//	date begun: 24 APR 2003
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <sys/mman.h>	// for mmap(), munmap()

char filename[] = "/dev/vram";

int main( int argc, char **argv )
{
	// open the device file and determine size
	int	mm = open( filename, O_RDWR );
	if ( mm < 0 ) { perror( filename ); exit(1); }
	int	vramsize = lseek( mm, 0, SEEK_END );
	printf( "\n\tvramsize=%d bytes (%d MB)\n", vramsize, vramsize >> 20 );
	
	// ask user to type in the desired frame-buffer address
	unsigned long	address;
	printf( "\nYour preferred frame-buffer address (hexadecimal): " );
	scanf( "%x", &address );
	printf( "\n" );

	// try to map the device-memory at the requested address
	int	prot = ( PROT_READ | PROT_WRITE );
	int	flags = MAP_SHARED;
	int	offset = 0;
	void	*aaddr = (void *)address;
	long	*vram;
	vram = (long*)mmap( aaddr, vramsize, prot, flags, mm, offset );
	printf( "\tAddress asked: %08X  Address given: %08X \n", aaddr, vram ); 

	// do some drawing (to verify the memory mapping)
	for (int i = 0; i < 1280; i++) vram[i] = 0x00FF0000;

	// unmap the device memory and exit
	munmap( vram, vramsize );
}