//-------------------------------------------------------------------
//	bluetext.cpp
//
//	This short demo program shows the essential steps needed for
//	executing 'Real Mode' code in Virtual-8086 Mode under Linux,
//	assuming i/o-sensitive instructions will not be encountered.
//
//	This demo is designed to be run from a text-mode console (no 
//	effect will be visible if executed from a graphics console).
//
//	NOTE: In order to allow writing to the system's video memory 
//	without requiring special privileges, this program relies on
//	the services provided by our 'dos.c' device-driver module. 
//
//	programmer: ALLAN CRUSE
//	written on: 26 MAY 2005
//-------------------------------------------------------------------

#include <stdio.h>		// for printf(), perror() 
#include <fcntl.h>		// for open() 
#include <stdlib.h>		// for exit() 
#include <sys/mman.h>		// for mmap()
#include <sys/vm86.h>		// for vm86()
#include <linux/linkage.h>	// for 'asmlinkage' attribute

#define PROT	( PROT_READ | PROT_WRITE )
#define FLAG	( MAP_FIXED | MAP_SHARED )

asmlinkage void blue( void );	// prevents C++ name-mangling
asm("	.code16			");
asm("	.align	16		");
asm("blue:			");
asm("	movw	$0xB800, %ax	");	
asm("	movw	%ax, %es	");
asm("	xorw	%di, %di	");
asm("	movb	$0x17, %al	");
asm("	movw	$0x4000, %cx	");
asm("nxpel:			");
asm("	movb	%al, %es:1(%di)	");
asm("	addw	$2, %di		");
asm("	loop	nxpel		");
asm("	hlt			");
asm("	.code32			");


int main( void )
{
	int	fd;

	// setup a memory-mapping for accessing video display memory
	void	*vram = (void*)0x000B8000;	// address of 32KB window
	if ( ( fd = open( "/dev/dos", O_RDWR ) ) < 0 )
		{ perror( "/dev/dos" ); exit(1); }
	if ( mmap( vram, 0x8000, PROT, FLAG, fd, (int)vram ) == MAP_FAILED )
		{ perror( "mmap /dev/dos" ); exit(1); }

	// setup a memory-mapping for accessing our vm86 code and stack 
	void	*prog = (void*)0x00010000;	// address of 64KB window
	if ( ( fd = open( "/dev/zero", O_RDWR ) ) < 0 )
		{ perror( "/dev/zero" ); exit(1); }
	if ( mmap( prog, 0x10000, PROT, FLAG, fd, 0 ) == MAP_FAILED )
		{ perror( "mmap /dev/zero" ); exit(1); }

	// now 'load' our 16-bit program-code into this memory region
	char	*dst = (char*)prog;
	char	*src = (char*)blue;
	for (int i = 0; i < 0x10000; i++)
		if ( ( dst[i] = src[i] ) == (char)0xF4 ) break;

	// compute starting addresses for the real-mode code and stack 
	int	initial_CS = ((int)prog) >> 4;
	int	initial_IP = 0;
	int	initial_SS = ((int)prog) >> 4;
	int	initial_SP = 0;
	
	// initialize data-structure for entering Virtual-8086 Mode
	struct vm86plus_struct	vm = {0};
	vm.regs.eip = initial_IP;
	vm.regs.cs = initial_CS;
	vm.regs.esp = initial_SP;
	vm.regs.ss = initial_SS;
	vm.regs.eflags = (1<<9);	// IF=1, IOPL=0
	vm.cpu_type = CPU_586;

	// execute in Virtual-8086 Mode (until 'hlt' is encounterd)
	vm86( VM86_ENTER, &vm );

	printf( "\nReturned successfully from Virtual-8086 Mode\n\n" );
}