#include	"u.h"#include	"lib.h"#include	"mem.h"#include	"dat.h"#include	"fns.h"#include	"io.h"#include	"ureg.h" /* *  8253 timer */enum{	T0cntr=	0x40,		/* counter ports */	T1cntr=	0x41,		/* ... */	T2cntr=	0x42,		/* ... */	Tmode=	0x43,		/* mode port */ 	/* commands */	Latch0=	0x00,		/* latch counter 0's value */	Load0=	0x30,		/* load counter 0 with 2 bytes */ 	/* modes */	Square=	0x36,		/* perioic square wave */ 	Freq=	1193182,	/* Real clock frequency */}; static int cpufreq = 66000000;static int cpumhz = 66;static int cputype = 486;static int loopconst = 100; /* *  delay for l milliseconds more or less.  delayloop is set by *  clockinit() to match the actual CPU speed. */voiddelay(int l){	aamloop(l*loopconst);} static voidclock(Ureg*, void*){	m->ticks++;	checkalarms();} voidclockinit(void){	ulong x, y;	/* change in counter */	ulong cycles, loops; 	switch(cputype = x86()){	case 386:		loops = 10000;		cycles = 32;		break;	case 486:		loops = 10000;		cycles = 22;		break;	default:		loops = 30000;		cycles = 23;		break;	} 	/*	 *  set vector for clock interrupts	 */	setvec(Clockvec, clock, 0); 	/*	 *  set clock for 1/HZ seconds	 */	outb(Tmode, Load0|Square);	outb(T0cntr, (Freq/HZ));	/* low byte */	outb(T0cntr, (Freq/HZ)>>8);	/* high byte */  	/*	 *  measure time for the loop	 *	 *			MOVL	loops,CX	 *	aaml1:	 	AAM	 *			LOOP	aaml1	 *	 *  the time for the loop should be independent from external	 *  cache's and memory system since it fits in the execution	 *  prefetch buffer.	 *	 */	outb(Tmode, Latch0);	x = inb(T0cntr);	x |= inb(T0cntr)<<8;	aamloop(loops);	outb(Tmode, Latch0);	y = inb(T0cntr);	y |= inb(T0cntr)<<8;	x -= y; 	/*	 *  counter  goes at twice the frequency, once per transition,	 *  i.e., twice per square wave	 */	x >>= 1; 	/* 	 *  figure out clock frequency and a loop multiplier for delay().	 */	cpufreq = loops*((cycles*Freq)/x);	loopconst = (cpufreq/1000)/cycles;	/* AAM+LOOP's for 1 ms */ 	/*	 *  add in possible .1% error and convert to MHz	 */	cpumhz = (cpufreq + cpufreq/1000)/1000000;}