nuclear@3: /*
nuclear@3: 256-color 3D graphics hack for real-mode DOS.
nuclear@3: Copyright (C) 2011  John Tsiombikas <nuclear@member.fsf.org>
nuclear@3: 
nuclear@3: This program is free software: you can redistribute it and/or modify
nuclear@3: it under the terms of the GNU General Public License as published by
nuclear@3: the Free Software Foundation, either version 3 of the License, or
nuclear@3: (at your option) any later version.
nuclear@3: 
nuclear@3: This program is distributed in the hope that it will be useful,
nuclear@3: but WITHOUT ANY WARRANTY; without even the implied warranty of
nuclear@3: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
nuclear@3: GNU General Public License for more details.
nuclear@3: 
nuclear@3: You should have received a copy of the GNU General Public License
nuclear@3: along with this program.  If not, see <http://www.gnu.org/licenses/>.
nuclear@3: */
nuclear@3: #include <stdio.h>
nuclear@3: #include <stdlib.h>
nuclear@3: #include <conio.h>
nuclear@3: #include <dos.h>
nuclear@3: #include <i86.h>
nuclear@3: #include "pit8254.h"
nuclear@3: 
nuclear@3: #define PIT_TIMER_INTR	8
nuclear@3: #define DOS_TIMER_INTR	0x1c
nuclear@3: 
nuclear@3: /* macro to divide and round to the nearest integer */
nuclear@3: #define DIV_ROUND(a, b) \
nuclear@3: 	((a) / (b) + ((a) % (b)) / ((b) / 2))
nuclear@3: 
nuclear@3: static void set_timer_reload(int reload_val);
nuclear@3: static void cleanup(void);
nuclear@3: static void __interrupt __far timer_irq();
nuclear@3: static void __interrupt __far dos_timer_intr();
nuclear@3: 
nuclear@3: static void (__interrupt __far *prev_timer_intr)();
nuclear@3: 
nuclear@3: static unsigned long ticks;
nuclear@3: static unsigned long tick_interval, ticks_per_dos_intr;
nuclear@3: static int inum;
nuclear@3: 
nuclear@3: void init_timer(int res_hz)
nuclear@3: {
nuclear@3: 	_disable();
nuclear@3: 
nuclear@3: 	if(res_hz > 0) {
nuclear@3: 		int reload_val = DIV_ROUND(OSC_FREQ_HZ, res_hz);
nuclear@3: 		set_timer_reload(reload_val);
nuclear@3: 
nuclear@3: 		tick_interval = DIV_ROUND(1000, res_hz);
nuclear@3: 		ticks_per_dos_intr = DIV_ROUND(65535L, reload_val);
nuclear@3: 
nuclear@3: 		inum = PIT_TIMER_INTR;
nuclear@3: 		prev_timer_intr = _dos_getvect(inum);
nuclear@3: 		_dos_setvect(inum, timer_irq);
nuclear@3: 	} else {
nuclear@3: 		tick_interval = 55;
nuclear@3: 
nuclear@3: 		inum = DOS_TIMER_INTR;
nuclear@3: 		prev_timer_intr = _dos_getvect(inum);
nuclear@3: 		_dos_setvect(inum, dos_timer_intr);
nuclear@3: 	}
nuclear@3: 	_enable();
nuclear@3: 
nuclear@3: 	atexit(cleanup);
nuclear@3: }
nuclear@3: 
nuclear@3: static void cleanup(void)
nuclear@3: {
nuclear@3: 	if(!prev_timer_intr) {
nuclear@3: 		return; /* init hasn't ran, there's nothing to cleanup */
nuclear@3: 	}
nuclear@3: 
nuclear@3: 	_disable();
nuclear@3: 	if(inum == PIT_TIMER_INTR) {
nuclear@3: 		/* restore the original timer frequency */
nuclear@3: 		set_timer_reload(65535);
nuclear@3: 	}
nuclear@3: 
nuclear@3: 	/* restore the original interrupt handler */
nuclear@3: 	_dos_setvect(inum, prev_timer_intr);
nuclear@3: 	_enable();
nuclear@3: }
nuclear@3: 
nuclear@3: void reset_timer(void)
nuclear@3: {
nuclear@3: 	ticks = 0;
nuclear@3: }
nuclear@3: 
nuclear@3: unsigned long get_msec(void)
nuclear@3: {
nuclear@3: 	return ticks * tick_interval;
nuclear@3: }
nuclear@3: 
nuclear@3: static void set_timer_reload(int reload_val)
nuclear@3: {
nuclear@3: 	outp(PORT_CMD, CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE);
nuclear@3: 	outp(PORT_DATA0, reload_val & 0xff);
nuclear@3: 	outp(PORT_DATA0, (reload_val >> 8) & 0xff);
nuclear@3: }
nuclear@3: 
nuclear@3: static void __interrupt __far dos_timer_intr()
nuclear@3: {
nuclear@3: 	ticks++;
nuclear@3: 	_chain_intr(prev_timer_intr);	/* DOES NOT RETURN */
nuclear@3: }
nuclear@3: 
nuclear@3: /* first PIC command port */
nuclear@3: #define PIC1_CMD	0x20
nuclear@3: /* end of interrupt control word */
nuclear@3: #define OCW2_EOI	(1 << 5)
nuclear@3: 
nuclear@3: static void __interrupt __far timer_irq()
nuclear@3: {
nuclear@3: 	static unsigned long dos_ticks;
nuclear@3: 
nuclear@3: 	ticks++;
nuclear@3: 
nuclear@3: 	if(++dos_ticks >= ticks_per_dos_intr) {
nuclear@3: 		/* I suppose the dos irq handler does the EOI so I shouldn't
nuclear@3: 		 * do it if I am to call the previous function
nuclear@3: 		 */
nuclear@3: 		dos_ticks = 0;
nuclear@3: 		_chain_intr(prev_timer_intr);	/* DOES NOT RETURN */
nuclear@3: 	} else {
nuclear@3: 		/* send EOI to the PIC */
nuclear@3: 		outp(PIC1_CMD, OCW2_EOI);
nuclear@3: 	}
nuclear@3: }