ref: e81c54ba2ecc673a4d5f8aed0e9b52841fe07b0d
dir: /os/boot.original/puma/clock.c/
#include "boot.h"
/*
* Control Word Read/Write Counter (mode 0) LSB, MSB
*/
#define PIT_RW_COUNTER0 0x30
#define PIT_RW_COUNTER1 0x70
#define PIT_RW_COUNTER2 0xB0
#define PIT_COUNTERLATCH0 0x00
#define PIT_COUNTERLATCH1 0x40
#define PIT_COUNTERLATCH2 0x80
#define PIT_MODE_0 0 /* Interrupt on Terminal Count */
#define PIT_MODE_1 2 /* Hardware Retriggeable One-shot */
#define PIT_MODE_2 4 /* Rate Generator */
#define PIT_MODE_3 6 /* Square Wave Mode */
#define PIT_MODE_4 8 /* Software Triggered Mode */
#define PIT_MODE_5 10 /* Hardware Triggered Mode (Retriggeable) */
/*
* Harris 82C54 Programmable Interval Timer
* On the Puma board the PIT is memory mapped
* starting at 0xf2000000 and with each of the 8-bit
* registers addressed on a consecutive 4-byte boundary.
*/
#undef inb
#undef outb
#define inb(port) ((*(uchar *)(port))&0xff)
#define outb(port, data) (*(uchar *)(port) = (data))
enum
{
Cnt0= 0xf2000000, /* counter locations */
Cnt1= 0xf2000004, /* ... */
Cnt2= 0xf2000008, /* ... */
Ctlw= 0xf200000c, /* control word register*/
/* commands */
Latch0= 0x00, /* latch counter 0's value */
Load0= 0x30, /* load counter 0 with 2 bytes */
Latch1= 0x40, /* latch counter 1's value */
Load1= 0x70, /* load counter 1 with 2 bytes */
/* modes */
Square= 0x06, /* periodic square wave */
RateGen= 0x04, /* rate generator */
Freq= 3686400, /* Real clock frequency */
};
static int cpufreq = 233000000;
static int aalcycles = 14;
static void
clockintr(Ureg*, void*)
{
m->ticks++;
checkalarms();
}
/*
* delay for l milliseconds more or less. delayloop is set by
* clockinit() to match the actual CPU speed.
*/
void
delay(int l)
{
l *= m->delayloop;
if(l <= 0)
l = 1;
aamloop(l);
}
void
microdelay(int l)
{
l *= m->delayloop;
l /= 1000;
if(l <= 0)
l = 1;
aamloop(l);
}
void
clockinit(void)
{
int x, y; /* change in counter */
int loops, incr;
/*
* set vector for clock interrupts
*/
setvec(V_TIMER0, clockintr, 0);
/*
* set clock for 1/HZ seconds
*/
outb(Ctlw, Load0|Square);
outb(Cnt0, (Freq/HZ)); /* low byte */
outb(Cnt0, (Freq/HZ)>>8); /* high byte */
/* find biggest loop that doesn't wrap */
incr = 16000000/(aalcycles*HZ*2);
x = 2000;
for(loops = incr; loops < 64*1024; loops += incr) {
/*
* measure time for the loop
* TEXT aamloop(SB), $-4
* _aamloop:
* MOVW R0, R0
* MOVW R0, R0
* MOVW R0, R0
* SUB $1, R0
* CMP $0, R0
* BNE _aamloop
* RET
*
* the time for the loop should be independent of external
* cache and memory system since it fits in the execution
* prefetch buffer.
*
*/
outb(Ctlw, Latch0);
x = inb(Cnt0);
x |= inb(Cnt0)<<8;
aamloop(loops);
outb(Ctlw, Latch0);
y = inb(Cnt0);
y |= inb(Cnt0)<<8;
x -= y;
if(x < 0)
x += Freq/HZ;
if(x > Freq/(3*HZ))
break;
}
/*
* 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*((aalcycles*Freq)/x);
m->delayloop = (cpufreq/1000)/aalcycles; /* AAMLOOPs for 1 ms */
/*
* add in possible .2% error and convert to MHz
*/
m->speed = (cpufreq + cpufreq/500)/1000000;
}