nuclear@33: #include <stdio.h>
nuclear@37: #include <time.h>
nuclear@33: #include "intr.h"
nuclear@33: #include "asmops.h"
nuclear@34: #include "timer.h"
nuclear@33: #include "config.h"
nuclear@33: 
nuclear@33: /* frequency of the oscillator driving the 8254 timer */
nuclear@33: #define OSC_FREQ_HZ		1193182
nuclear@33: 
nuclear@33: /* macro to divide and round to the nearest integer */
nuclear@33: #define DIV_ROUND(a, b) ((a) / (b) + ((a) % (b)) / ((b) / 2))
nuclear@33: 
nuclear@33: /* I/O ports connected to the 8254 */
nuclear@33: #define PORT_DATA0	0x40
nuclear@33: #define PORT_DATA1	0x41
nuclear@33: #define PORT_DATA2	0x42
nuclear@33: #define PORT_CMD	0x43
nuclear@33: 
nuclear@33: /* command bits */
nuclear@33: #define CMD_CHAN0			0
nuclear@33: #define CMD_CHAN1			(1 << 6)
nuclear@33: #define CMD_CHAN2			(2 << 6)
nuclear@33: #define CMD_RDBACK			(3 << 6)
nuclear@33: 
nuclear@33: #define CMD_LATCH			0
nuclear@33: #define CMD_ACCESS_LOW		(1 << 4)
nuclear@33: #define CMD_ACCESS_HIGH		(2 << 4)
nuclear@33: #define CMD_ACCESS_BOTH		(3 << 4)
nuclear@33: 
nuclear@33: #define CMD_OP_INT_TERM		0
nuclear@33: #define CMD_OP_ONESHOT		(1 << 1)
nuclear@33: #define CMD_OP_RATE			(2 << 1)
nuclear@33: #define CMD_OP_SQWAVE		(3 << 1)
nuclear@33: #define CMD_OP_SOFT_STROBE	(4 << 1)
nuclear@33: #define CMD_OP_HW_STROBE	(5 << 1)
nuclear@33: 
nuclear@33: #define CMD_MODE_BIN		0
nuclear@33: #define CMD_MODE_BCD		1
nuclear@33: 
nuclear@33: 
nuclear@33: static void intr_handler();
nuclear@33: 
nuclear@33: 
nuclear@33: void init_timer(void)
nuclear@33: {
nuclear@34: 	/* calculate the reload count: round(osc / freq) */
nuclear@34: 	int reload_count = DIV_ROUND(OSC_FREQ_HZ, TICK_FREQ_HZ);
nuclear@33: 
nuclear@33: 	/* set the mode to square wave for channel 0, both low
nuclear@34: 	 * and high reload count bytes will follow...
nuclear@33: 	 */
nuclear@33: 	outb(CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE, PORT_CMD);
nuclear@33: 
nuclear@34: 	/* write the low and high bytes of the reload count to the
nuclear@33: 	 * port for channel 0
nuclear@33: 	 */
nuclear@34: 	outb(reload_count & 0xff, PORT_DATA0);
nuclear@34: 	outb((reload_count >> 8) & 0xff, PORT_DATA0);
nuclear@33: 
nuclear@33: 	/* set the timer interrupt handler */
nuclear@35: 	interrupt(IRQ_TO_INTR(0), intr_handler);
nuclear@33: }
nuclear@33: 
nuclear@33: /* This will be called by the interrupt dispatcher approximately
nuclear@33:  * every 1/250th of a second, so it must be extremely fast.
nuclear@33:  * For now, just increasing a tick counter will suffice.
nuclear@33:  */
nuclear@33: static void intr_handler()
nuclear@33: {
nuclear@33: 	nticks++;
nuclear@33: }