/*
NAME
	pageflip - test hardware page flipping

SYNOPSIS
	pageflip <offset>

DESCRIPTION
	pageflip is used to test hardware page flipping on graphic cards
	supporting standard VGA registers while running an X Server.

	To obtain meaningful results, a virtual screen must be active with an
	horizontal resolution set to the double of the viewport horizontal
	resolution. For example, a 1024x768 viewport with a 2048x768 virtual
	screen.

	The application is controlled using these interactive commands:

	q	quit the application
	1	set the CRTC Start Address Register to 0
	2	set the CRTC Start Address Register to <offset>

OPTIONS
	<offset>
		Set the offset value as a number of pixel columns that should
		correspond to the width of the current viewport. For example
		1920 for a 3840x1080 virtual screen.

AUTHOR
	Frédéric Lopez <frederic.lopez@free.fr>

	12 September 2010
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/io.h>
#include <errno.h>

// Define the Address Register for CRTC access
#define CRTC_ADDR_REG 0x3D4
// Define the Data Register for CRTC access
#define CRTC_DATA_REG 0x3D5

// Set the CRTC Start Adress Register
static void set_vga_start(int offset)
{
	// Set the CRTC Start Address Low Register
	outb(0x0D, CRTC_ADDR_REG);
	outb(offset & 0xFF, CRTC_DATA_REG);

	// Set the CRTC Start Address High Register
	outb(0x0C, CRTC_ADDR_REG);
	outb(offset >> 8, CRTC_DATA_REG);
}

int main(int argc, char *argv[])
{
	int key, offset;
	char *p;

	// Test the number of command-line arguments
	if (argc != 2)
	{
		printf("Usage: pageflip <offset>\n");
		exit(EXIT_FAILURE);
	}

	// Test if the argument is an integer
	errno = 0;
	offset = strtol(argv[1], &p, 10);
	if (errno != 0 || *p != 0 || p == argv[1])
	{
		printf("Error: offset value must be an integer!\n");
		exit(EXIT_FAILURE);
	}

	// Change the I/O privilege level to allow access to VGA registers
	if (iopl(3) != 0)
	{
		printf("Warning: unable to modify the I/O privilege level!\n");
	}

	// Show interactive commands help
	printf("Quit with 'q'.\n");
	printf("Page 1 with '1'.\n");
	printf("Page 2 with '2'.\n");
	
	while ((key = getchar()) != 'q')
	{
		switch (key)
		{
			case '1' :
				// Set Start Address Register to 0
				set_vga_start(0);
				printf("Page 1.\n");
				break;
			case '2' :
				// Set Start Address Register to <offset>
				set_vga_start(offset);
				printf("Page 2.\n");
				break;
		}
	}

	// Restore the default I/O privilege level
	if (iopl(0) != 0)
	{
		printf("Warning: unable to restore the default I/O privilege level!\n");
	}
	
	printf("Done.\n");
      
	return EXIT_SUCCESS;
}