//-------------------------------------------------------------------
//	newzero.cpp
//
//	This program shows how the VGA's Graphics Controller can be
//	used to permit an application (with suitable privileges) to 
//	modify a glyph in the system's character generator ram.  It
//	installs a new image for the zero character ('0') which has
//	ascii code 0x30.  For correct operation this program should
//	be executed in standard 80x25 text mode (VGA mode 3) from a 
//	command shell having 'root' privileges.   
//
//	Reference:  Richard Wilton, "Programmer's Guide to PC Video 
//	Systems (Second Edition)," Microsoft Press (1994), 294-299.
//
//	NOTE: Run the 'mode3' program to restore the standard zero.
//
//	programmer: ALLAN CRUSE
//	written on: 04 SEP 2003
//	revised on: 09 SEP 2003
//-------------------------------------------------------------------

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

#define GRAF_PORT 0x3CE		// for i/o to the Graphics Controller
#define TSEQ_PORT 0x3C4		// for i/o to the VGA Timer-Sequencer


unsigned char newglyph[ 16 ] = 	{
				0x00,	// 00000000
				0x00,	// 00000000
				0x7C,	// 01111100
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x82,	// 10000010
				0x7C,	// 01111100
				0x00,	// 00000000
				0x00,	// 00000000
				0x00,	// 00000000
				0x00	// 00000000
				};


void map_device_memory( int base, int size );





int main( int argc, char **argv )
{
	// map the VGA memory window into the user's address-space 
	int	base = 0x000A0000;	// beginning of VGA window
	int	size = (128<<10);	// length of window = 128K
	map_device_memory( base, size );	

	// display some sample text that has a few zeros within it
	printf( "\033[H\033[J\n\n" );	// start with a clear screen
	printf( "\nTest message #1: one kilobyte equals 1024 bytes" );
	printf( "\nTest message #2: one megabyte equals 1024 kilobytes" );
	printf( "\nTest message #3: one gigabyte equals 1024 megabytes" );
	printf( "\n\nOK, to see a new glyph for zero, press <ENTER> " );
	getchar();
	
	// make sure we are allowed execute  i/o instructions
	if ( iopl( 3 ) ) { perror( "iopl" ); exit(1); }

	// prologue (makes character ram accessible to the cpu)
	outw( 0x0100, TSEQ_PORT );	// enter synchronous reset
	outw( 0x0402, TSEQ_PORT );	// write only to map 2
	outw( 0x0704, TSEQ_PORT );	// use sequential addressing
	outw( 0x0300, TSEQ_PORT );	// leave synchronous reset
	outw( 0x0204, GRAF_PORT );	// select map 2 for reads
	outw( 0x0005, GRAF_PORT );	// disable odd-even addressing
	outw( 0x0006, GRAF_PORT );	// map starts at 0xA000:0000

	// load our new image for '0' into character generator ram 
	unsigned char	*vram = (unsigned char*)base;
	int		zlocn = 0x30 * 32;
	for (int i = 0; i < 16; i++) vram[ zlocn + i ] = newglyph[ i ];
	
	// epilogue (makes character ram inaccessible to the cpu)
	outw( 0x0100, TSEQ_PORT );	// enter synchronous reset
	outw( 0x0302, TSEQ_PORT );	// write to maps 0 and 1
	outw( 0x0304, TSEQ_PORT );	// use odd-even addressing
	outw( 0x0300, TSEQ_PORT );	// leave synchronous reset
	outw( 0x0004, GRAF_PORT );	// select map 0 for reads
	outw( 0x1005, GRAF_PORT );	// enable odd-even addressing
	outw( 0x0E06, GRAF_PORT );	// map starts at 0xB800:0000
}


void map_device_memory( int base, int size )
{	
	int	fd = open( "/dev/mem", O_RDWR );
	if ( fd < 0 ) { perror( "/dev/mem" ); exit(1); }
	int	prot = PROT_READ | PROT_WRITE;
	int	flag = MAP_FIXED | MAP_SHARED;
	void	*mm = (void*)base;
	if ( mmap( mm, size, prot, flag, fd, base ) == MAP_FAILED )
		{ perror( "mmap" ); exit(1); }
}