//-------------------------------------------------------------------
//	redband.cpp
//
//	This code will illustrate the role of the graphics display
//	memory in controlling the color of screen picture-elements
//	(pixels) if programmed for the so-called 'truecolor' mode.  
//
//		to compile:  $ g++ redband.cpp -o redband
//		to execute:  $ ./redband
//
//	NOTE: This program is designed for execution solely on our 
//	Gateway NV53A laptop computer (in 1024-by-768 resolution),
//	and requires installing our customized device-driver named
//	'gateway.c' to allow access to the graphics display memory
//	plus the Radeon graphics engine's memory-mapped registers.
//
//	programmer: ALLAN CRUSE
//	written on: 22 MAR 2011
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for lseek()  
#include <sys/mman.h>	// for mmap()
#include <sys/ioctl.h>	// for ioctl()

#define VRAM_BASE	0x80000000
#define GET_CRTC_START_ADDRESS	0

const unsigned int	hpitch = 1024;
unsigned int		*fb;

int main( int argc, char **argv )
{
	// map the graphics display memory into user's address-space
	int	fd = open( "/dev/vram", O_RDWR );
	if ( fd < 0 ) { perror( "/dev/vram" ); exit(1); }
	int	size = lseek( fd, 0, SEEK_END );
	int	prot = PROT_READ | PROT_WRITE;
	int	flag = MAP_FIXED | MAP_SHARED;
	void	*mm = (void *)VRAM_BASE;
	if ( mmap( mm, size, prot, flag, fd, 0 ) == MAP_FAILED )
		{ perror( "mmap" ); exit(1); }

	// determine the current address of the GPU's frame-buffer
	unsigned int	crtc_start_address = 0;
	if ( ioctl( fd, GET_CRTC_START_ADDRESS, &crtc_start_address ) < 0 )
		{ perror( "ioctl" ); exit(1); }
	unsigned int	fb_offset = crtc_start_address & 0x3FFFFFFF;
	printf( " FRAME BUFFER OFFSET = 0x%08X \n", fb_offset );
	fb = (unsigned int *)( VRAM_BASE + fb_offset );

	// fill the upper 40 scanlines with blue-colored pixels
	unsigned int	color = 0x00FF0000; 	// red	
	for (int i = 0; i < 40 * hpitch; i++) fb[i] = color;
}