clock.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#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 uvlong cpuhz = 66000000;
static int cpumhz = 66;
static int loopconst = 100;
int cpuidax, cpuiddx;
int havetsc;

extern void _cycles(uvlong*);		/* in l.s */
extern void wrmsr(int, vlong);

static void
clockintr(Ureg*, void*)
{
	m->ticks++;
	checkalarms();
}

#define STEPPING(x)	((x)&0xf)
#define X86MODEL(x)	(((x)>>4)&0xf)
#define X86FAMILY(x)	(((x)>>8)&0xf)

enum
{
	/* flags */
	CpuidFPU	= 0x001,	/* on-chip floating point unit */
	CpuidMCE	= 0x080,	/* machine check exception */
	CpuidCX8	= 0x100,	/* CMPXCHG8B instruction */
};

typedef struct
{
	int family;
	int model;
	int aalcycles;
	char *name;
} X86type;

X86type x86intel[] =
{
	{ 4,	0,	22,	"486DX", },	/* known chips */
	{ 4,	1,	22,	"486DX50", },
	{ 4,	2,	22,	"486SX", },
	{ 4,	3,	22,	"486DX2", },
	{ 4,	4,	22,	"486SL", },
	{ 4,	5,	22,	"486SX2", },
	{ 4,	7,	22,	"DX2WB", },	/* P24D */
	{ 4,	8,	22,	"DX4", },	/* P24C */
	{ 4,	9,	22,	"DX4WB", },	/* P24CT */
	{ 5,	0,	23,	"P5", },
	{ 5,	1,	23,	"P5", },
	{ 5,	2,	23,	"P54C", },
	{ 5,	3,	23,	"P24T", },
	{ 5,	4,	23,	"P55C MMX", },
	{ 5,	7,	23,	"P54C VRT", },
	{ 6,	1,	16,	"PentiumPro", },/* trial and error */
	{ 6,	3,	16,	"PentiumII", },
	{ 6,	5,	16,	"PentiumII/Xeon", },
	{ 6,	6,	16,	"Celeron", },
	{ 6,	7,	16,	"PentiumIII/Xeon", },
	{ 6,	8,	16,	"PentiumIII/Xeon", },
	{ 6,	0xB,	16,	"PentiumIII/Xeon", },
	{ 0xF,	1,	16,	"P4", },	/* P4 */
	{ 0xF,	2,	16,	"PentiumIV/Xeon", },

	{ 3,	-1,	32,	"386", },	/* family defaults */
	{ 4,	-1,	22,	"486", },
	{ 5,	-1,	23,	"P5", },
	{ 6,	-1,	16,	"P6", },
	{ 0xF,	-1,	16,	"P4", },	/* P4 */

	{ -1,	-1,	16,	"unknown", },	/* total default */
};


/*
 * The AMD processors all implement the CPUID instruction.
 * The later ones also return the processor name via functions
 * 0x80000002, 0x80000003 and 0x80000004 in registers AX, BX, CX
 * and DX:
 *	K5	"AMD-K5(tm) Processor"
 *	K6	"AMD-K6tm w/ multimedia extensions"
 *	K6 3D	"AMD-K6(tm) 3D processor"
 *	K6 3D+	?
 */
static X86type x86amd[] =
{
	{ 5,	0,	23,	"AMD-K5", },	/* guesswork */
	{ 5,	1,	23,	"AMD-K5", },	/* guesswork */
	{ 5,	2,	23,	"AMD-K5", },	/* guesswork */
	{ 5,	3,	23,	"AMD-K5", },	/* guesswork */
	{ 5,	6,	11,	"AMD-K6", },	/* trial and error */
	{ 5,	7,	11,	"AMD-K6", },	/* trial and error */
	{ 5,	8,	11,	"AMD-K6-2", },	/* trial and error */
	{ 5,	9,	11,	"AMD-K6-III", },/* trial and error */

	{ 6,	1,	11,	"AMD-Athlon", },/* trial and error */
	{ 6,	2,	11,	"AMD-Athlon", },/* trial and error */

	{ 4,	-1,	22,	"Am486", },	/* guesswork */
	{ 5,	-1,	23,	"AMD-K5/K6", },	/* guesswork */
	{ 6,	-1,	11,	"AMD-Athlon", },/* guesswork */
	{ 0xF,	-1,	11,	"AMD64", },	/* guesswork */

	{ -1,	-1,	11,	"unknown", },	/* total default */
};

static X86type	*cputype;


void
delay(int millisecs)
{
	millisecs *= loopconst;
	if(millisecs <= 0)
		millisecs = 1;
	aamloop(millisecs);
}

void
microdelay(int microsecs)
{
	microsecs *= loopconst;
	microsecs /= 1000;
	if(microsecs <= 0)
		microsecs = 1;
	aamloop(microsecs);
}

extern void cpuid(char*, int*, int*);

X86type*
cpuidentify(void)
{
	int family, model;
	X86type *t;
	char cpuidid[16];
	int cpuidax, cpuiddx;

	cpuid(cpuidid, &cpuidax, &cpuiddx);
	if(strncmp(cpuidid, "AuthenticAMD", 12) == 0)
		t = x86amd;
	else
		t = x86intel;
	family = X86FAMILY(cpuidax);
	model = X86MODEL(cpuidax);
	if (0)
		print("cpuidentify: cpuidax 0x%ux cpuiddx 0x%ux\n",
			cpuidax, cpuiddx);
	while(t->name){
		if((t->family == family && t->model == model)
		|| (t->family == family && t->model == -1)
		|| (t->family == -1))
			break;
		t++;
	}
	if(t->name == nil)
		panic("cpuidentify");

	if(cpuiddx & 0x10){
		havetsc = 1;
		if(cpuiddx & 0x20)
			wrmsr(0x10, 0);
	}

	return t;
}

void
clockinit(void)
{
	uvlong a, b, cpufreq;
	int loops, incr, x, y;
	X86type *t;

	/*
	 *  set vector for clock interrupts
	 */
	setvec(VectorCLOCK, clockintr, 0);

	t = cpuidentify();

	/*
	 *  set clock for 1/HZ seconds
	 */
	outb(Tmode, Load0|Square);
	outb(T0cntr, (Freq/HZ));	/* low byte */
	outb(T0cntr, (Freq/HZ)>>8);	/* high byte */

	/*
	 * Introduce a little delay to make sure the count is
	 * latched and the timer is counting down; with a fast
	 * enough processor this may not be the case.
	 * The i8254 (which this probably is) has a read-back
	 * command which can be used to make sure the counting
	 * register has been written into the counting element.
	 */
	x = (Freq/HZ);
	for(loops = 0; loops < 100000 && x >= (Freq/HZ); loops++){
		outb(Tmode, Latch0);
		x = inb(T0cntr);
		x |= inb(T0cntr)<<8;
	}

	/* find biggest loop that doesn't wrap */
	incr = 16000000/(t->aalcycles*HZ*2);
	x = 2000;
	for(loops = incr; loops < 64*1024; loops += incr) {
	
		/*
		 *  measure time for the loop
		 *
		 *			MOVL	loops,CX
		 *	aaml1:	 	AAM
		 *			LOOP	aaml1
		 *
		 *  the time for the loop should be independent of external
		 *  cache and memory system since it fits in the execution
		 *  prefetch buffer.
		 *
		 */
		outb(Tmode, Latch0);
		if(havetsc)
			_cycles(&a);
		x = inb(T0cntr);
		x |= inb(T0cntr)<<8;
		aamloop(loops);
		outb(Tmode, Latch0);
		if(havetsc)
			_cycles(&b);
		y = inb(T0cntr);
		y |= inb(T0cntr)<<8;
		x -= y;
	
		if(x < 0)
			x += Freq/HZ;

		if(x > Freq/(3*HZ))
			break;
	}

	/*
 	 *  figure out clock frequency and a loop multiplier for delay().
	 *  counter  goes at twice the frequency, once per transition,
	 *  i.e., twice per square wave
	 */
	cpufreq = (vlong)loops*((t->aalcycles*2*Freq)/x);
	loopconst = (cpufreq/1000)/t->aalcycles;	/* AAM+LOOP's for 1 ms */

	if(havetsc){
		/* counter goes up by 2*Freq */
		b = (b-a)<<1;
		b *= Freq;
		b /= x;

		/*
		 *  round to the nearest megahz
		 */
		cpumhz = (b+500000)/1000000L;
		cpuhz = b;
	}
	else{
		/*
		 *  add in possible .5% error and convert to MHz
		 */
		cpumhz = (cpufreq + cpufreq/200)/1000000;
		cpuhz = cpufreq;
	}

	if(debug){
		int timeo;

		print("%dMHz %s loop %d\n", cpumhz, t->name, loopconst);
		print("tick...");
		for(timeo = 0; timeo < 10; timeo++)
			delay(1000);
		print("tock...\n");
	}
}