ben-blinkenlights/video/video.c

/*
 * video.c - Output CGA ? video
 *
 * Written 2011 by Werner Almesberger
 * Copyright 2011 Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

/*
 * WARNING: this program does very nasty things to the Ben and it doesn't
 * like company. In particular, it resents:
 *
 * - the MMC driver - disable it with
 *   echo jz4740-mmc.0 >/sys/bus/platform/drivers/jz4740-mmc/unbind
 * - the AT86RF230/1 kernel driver - use a kernel that doesn't have it
 * - anything that accesses the screen - kill GUI, X server, etc.
 * - the screen blanker - either disable it or make sure the screen stays
 *   dark, e.g., with
 *   echo 1 >/sys/devices/platform/jz4740-fb/graphics/fb0/blank
 * - probably a fair number of other daemons and things as well - best to
 *   kill them all.
 */


#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>


#define	DAT0		(1 << 10)
#define	DAT1		(1 << 11)
#define	DAT2		(1 << 12)
#define	DAT3		(1 << 13)
#define	CMD		(1 << 8)
#define	CLK		(1 << 9)

#define	R		DAT2
#define	G		DAT0
#define	B		DAT1
#define	HSYNC		CMD
#define	VSYNC		DAT3

#define	TIMER		7


#define	PAGE_SIZE	4096
#define	SOC_BASE	0x10000000
#define	DEFAULT_COUNT	(1000*1000)


/* ----- Ben hardware ------------------------------------------------------ */


static volatile uint32_t *icmr, *icmsr, *icmcr;
static uint32_t old_icmr;

static volatile uint32_t *clkgr;
static uint32_t old_clkgr;

static volatile uint32_t *pdpin, *pddats, *pddatc;
static volatile uint32_t *pddirs, *pddirc;

static volatile uint32_t *tssr, *tscr;
static volatile uint32_t *tesr, *tecr;
static volatile uint32_t *tcsr, *tdfr, *tcnt;


static void disable_interrupts(void)
{
	/*
	 * @@@ Race condition alert ! If we get interrupted/preempted between
	 * reading ICMR and masking all interrupts, and the code that runs
	 * between these two operations changes ICMR, then we may set an
	 * incorrect mask when restoring interrupts, which may hang the system.
	 */

	old_icmr = *icmr;
	*icmsr = 0xffffffff;
}


static void enable_interrupts(void)
{
	*icmcr = ~old_icmr;
}


/*
 * @@@ Disabling the LCD clock will halng operations that depend on the LCD
 * subsystem to advance. This includes the screen saver.
 */

static void disable_lcd(void)
{
	old_clkgr = *clkgr;
	*clkgr = old_clkgr | 1 << 10;
}


static void enable_lcd(void)
{
	*clkgr = old_clkgr;
}


static void get_timer(void)
{
	*tscr = 1 << TIMER;	/* enable clock */
	*tcsr = 1;		/* count at PCLK/1 */
	*tdfr = 0xffff;		/* count to 0xffff */
	*tesr = 1 << TIMER;
}


static void release_timer(void)
{
	*tecr = 1 << TIMER;
	*tssr = 1 << TIMER;
}


static void ben_setup(void)
{
	volatile void *base;
	int fd;

	fd = open("/dev/mem", O_RDWR | O_SYNC);
	if (fd < 0) {
		perror("/dev/mem");
		exit(1);
	}
	base = mmap(NULL, PAGE_SIZE*3*16, PROT_READ | PROT_WRITE, MAP_SHARED,
	    fd, SOC_BASE);
	if (base == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}

	icmr = base+0x1004;
	icmsr = base+0x1008;
	icmcr = base+0x100c;

	clkgr = base+0x20;

	pdpin = base+0x10300;
	pddats = base+0x10314;
	pddatc = base+0x10318;

	pddirs = base+0x10364;
	pddirc = base+0x10368;

	tssr = base+0x202c;
	tscr = base+0x203c;

	tesr = base+0x2014;
	tecr = base+0x2018;

	tcsr = base+0x204c+0x10*TIMER;
	tdfr = base+0x2040+0x10*TIMER;
	tcnt = base+0x2048+0x10*TIMER;

	/*
	 * Ironically, switching the LCD clock on and off many times only
	 * increases the risk of a hang. Therefore, we leave stop it during
	 * all the measurements and only enable it again at the end.
	 */
	disable_lcd();
	get_timer();
}


static void cleanup(void)
{
	release_timer();
	enable_lcd();
}


/* ----- Interface --------------------------------------------------------- */


void setup(void)
{
	mlockall(MCL_CURRENT | MCL_FUTURE);
	ben_setup();
	*pddirs = R | G | B | HSYNC | VSYNC;
}


static uint32_t pick(int set, int bit, uint32_t val)
{
	return set == bit ? val >> 8 : 0;
}


static uint32_t pattern(int r, int g, int b, int hsync, int vsync, int set)
{
	return pick(set, r, R) | pick(set, g, G) | pick(set, b, B) |
	    pick(set, hsync, HSYNC) | pick(set, vsync, VSYNC);
}


#define	BURST		32

#define	PREFETCH_HSYNC	160
#define	PREFETCH_HFRONT	(160-PREFETCH_HSYNC)
#define	DELAY_HFRONT	30
#define	DELAY_HBACK	40
//#define	DELAY_VSYNC	3500
//#define	DELAY_VFRONT	56000
//#define	DELAY_VBACK	28000
#define	DELAY_VFRONT	1500
#define	DELAY_LINE	1800
#define	DELAY_HSYNC	210


static inline void prefetch(const uint8_t *prefetch, int words)
{
	volatile const uint8_t *p = prefetch;

	while (p != prefetch+words) {
		(void) *p;
		p += BURST;
	}
}


static void until(uint16_t cycles)
{
	while ((*tcnt & 0xffff) < cycles);
}

#define	US(us)	((uint16_t) ((us)*112))

static void line(const uint8_t *line, const uint8_t *fetch)
{
	const uint8_t *p = line;
//volatile uint8_t pat = R | B | G;
	/* HSYNC */
	*tcnt = 0;
	*pddatc = HSYNC;
//	prefetch(fetch, PREFETCH_HSYNC);
	prefetch(fetch, 160);
	until(US(3.77));
//	*tcnt = 0;
	*pddats = HSYNC;

	/* Front porch */
//	prefetch(fetch+PREFETCH_HSYNC, PREFETCH_HFRONT);
//	until(US(3.77+1.79-3.77));
	until(US(3.77+1.79));

	while (p != line+320) {
		*pddats = *p++ << 8;//pat; //R | G | B; //*p++;
		*pddatc = *p++ << 8;//pat;//R | G | B; // *p++;
	}

	/* Back porch */
//	until(US(31.77-3.77));
	until(US(31.77));
	until(US(36));
}


static void hdelay(int cycles)
{
	while (cycles--) {
		*tcnt = 0;
		*pddatc = HSYNC;
		until(US(3.77));
		*pddats = HSYNC;
		until(US(31.77));
	until(US(36));
	}
}


static void frame(const uint8_t *f)
{
	const uint8_t *p;

	/* VSYNC */
	*pddatc = VSYNC;
	hdelay(2);
	*pddats = VSYNC;

	/* Front porch */
	*tcnt = 0;
	*pddatc = HSYNC;
//	prefetch(f, PREFETCH_HSYNC);
	until(US(3.77));
//	*tcnt = 0;
	*pddats = HSYNC;

//	prefetch(f+PREFETCH_HSYNC, PREFETCH_HFRONT);
	prefetch(f, 160);
//	until(US(31.77-3.77));
	until(US(31.77));
	until(US(36));
	hdelay(31);

	for (p = f; p != f+240*320; p += 320) {
		line(p, p+160);
		line(p, p+320);
	}

	/* Back porch */
	hdelay(14);
}


static void tricolor(uint32_t *f)
{
	int i;

	for (i = 0; i != 320*240/3; i++) {
		f[i & ~1] = R;
		f[i | 1] = G | B;
	}
	for (; i != 320*240*2/3; i++) {
		f[i & ~1] = G;
		f[i | 1] = R | B;
	}

	for (; i != 320*240; i++) {
		f[i & ~1] = B;
		f[i | 1] = R | G;
	}
}


static void grid(uint8_t *f)
{
	static uint32_t col[8] = {
		R | G | B,
		R,
		R | G,
		G,
		G | B,
		B,
		R | B,
		R | G | B,
	};
	int i, x, y;

	for (i = 0; i != 8; i++) {
		x = i*40+20;
		for (y = 0; y != 240; y++) {
			f[y*320+x] = f[y*320+x+1] = col[i] >> 8;
		}
	}
}


static void session(int n)
{
	uint8_t f[320*(240+1)];
	int i;

	memset(f, 0, sizeof(f));
	grid(f);

	disable_interrupts();

	for (i = 0; i != n; i++)
		frame(f);

	enable_interrupts();
}


int main(int argc, char **argv)
{
	setup();
	session(atoi(argv[1]));
	cleanup();
	return 0;
}