ref: 83246e296ea433b65b9d295b5e08fedd39ff1ab7
dir: /os/pc/i8253.c/
#include "u.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "io.h"
/*
* 8253 timer
*/
enum
{
T0cntr= 0x40, /* counter ports */
T1cntr= 0x41, /* ... */
T2cntr= 0x42, /* ... */
Tmode= 0x43, /* mode port (control word register) */
T2ctl= 0x61, /* counter 2 control port */
/* commands */
Latch0= 0x00, /* latch counter 0's value */
Load0l= 0x10, /* load counter 0's lsb */
Load0m= 0x20, /* load counter 0's msb */
Load0= 0x30, /* load counter 0 with 2 bytes */
Latch1= 0x40, /* latch counter 1's value */
Load1l= 0x50, /* load counter 1's lsb */
Load1m= 0x60, /* load counter 1's msb */
Load1= 0x70, /* load counter 1 with 2 bytes */
Latch2= 0x80, /* latch counter 2's value */
Load2l= 0x90, /* load counter 2's lsb */
Load2m= 0xa0, /* load counter 2's msb */
Load2= 0xb0, /* load counter 2 with 2 bytes */
/* 8254 read-back command: everything > pc-at has an 8254 */
Rdback= 0xc0, /* readback counters & status */
Rdnstat=0x10, /* don't read status */
Rdncnt= 0x20, /* don't read counter value */
Rd0cntr=0x02, /* read back for which counter */
Rd1cntr=0x04,
Rd2cntr=0x08,
/* modes */
ModeMsk=0xe,
Square= 0x6, /* periodic square wave */
Trigger=0x0, /* interrupt on terminal count */
Sstrobe=0x8, /* software triggered strobe */
/* T2ctl bits */
T2gate= (1<<0), /* enable T2 counting */
T2spkr= (1<<1), /* connect T2 out to speaker */
T2out= (1<<5), /* output of T2 */
Freq= 1193182, /* Real clock frequency */
Tickshift=8, /* extra accuracy */
MaxPeriod=Freq/HZ,
MinPeriod=Freq/(100*HZ),
};
typedef struct I8253 I8253;
struct I8253
{
Lock;
ulong period; /* current clock period */
int enabled;
uvlong hz;
ushort last; /* last value of clock 1 */
uvlong ticks; /* cumulative ticks of counter 1 */
ulong periodset;
};
I8253 i8253;
void
i8253init(void)
{
int loops, x;
ioalloc(T0cntr, 4, 0, "i8253");
ioalloc(T2ctl, 1, 0, "i8253.cntr2ctl");
i8253.period = Freq/HZ;
/*
* enable a 1/HZ interrupt for providing scheduling interrupts
*/
outb(Tmode, Load0|Square);
outb(T0cntr, (Freq/HZ)); /* low byte */
outb(T0cntr, (Freq/HZ)>>8); /* high byte */
/*
* enable a longer period counter to use as a clock
*/
outb(Tmode, Load2|Square);
outb(T2cntr, 0); /* low byte */
outb(T2cntr, 0); /* high byte */
x = inb(T2ctl);
x |= T2gate;
outb(T2ctl, x);
/*
* 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;
}
}
void
guesscpuhz(int aalcycles)
{
int loops, incr, x, y;
uvlong a, b, cpufreq;
/* 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
*
* 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);
cycles(&a);
x = inb(T0cntr);
x |= inb(T0cntr)<<8;
aamloop(loops);
outb(Tmode, Latch0);
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().
* n.b. counter goes up by 2*Freq
*/
cpufreq = (vlong)loops*((aalcycles*2*Freq)/x);
m->loopconst = (cpufreq/1000)/aalcycles; /* AAM+LOOP's for 1 ms */
if(m->havetsc){
/* counter goes up by 2*Freq */
b = (b-a)<<1;
b *= Freq;
b /= x;
/*
* round to the nearest megahz
*/
m->cpumhz = (b+500000)/1000000L;
m->cpuhz = b;
m->cyclefreq = b;
} else {
/*
* add in possible 0.5% error and convert to MHz
*/
m->cpumhz = (cpufreq + cpufreq/200)/1000000;
m->cpuhz = cpufreq;
}
i8253.hz = Freq<<Tickshift;
}
void
i8253timerset(uvlong next)
{
long period;
ulong want;
ulong now;
period = MaxPeriod;
if(next != 0){
want = next>>Tickshift;
now = i8253.ticks; /* assuming whomever called us just did fastticks() */
period = want - now;
if(period < MinPeriod)
period = MinPeriod;
else if(period > MaxPeriod)
period = MaxPeriod;
}
/* hysteresis */
if(i8253.period != period){
ilock(&i8253);
/* load new value */
outb(Tmode, Load0|Square);
outb(T0cntr, period); /* low byte */
outb(T0cntr, period >> 8); /* high byte */
/* remember period */
i8253.period = period;
i8253.periodset++;
iunlock(&i8253);
}
}
static void
i8253clock(Ureg* ureg, void*)
{
timerintr(ureg, 0);
}
void
i8253enable(void)
{
i8253.enabled = 1;
i8253.period = Freq/HZ;
intrenable(IrqCLOCK, i8253clock, 0, BUSUNKNOWN, "clock");
}
void
i8253link(void)
{
}
/*
* return the total ticks of counter 2. We shift by
* 8 to give timesync more wriggle room for interpretation
* of the frequency
*/
uvlong
i8253read(uvlong *hz)
{
ushort y, x;
uvlong ticks;
if(hz)
*hz = Freq<<Tickshift;
ilock(&i8253);
outb(Tmode, Latch2);
y = inb(T2cntr);
y |= inb(T2cntr)<<8;
if(y < i8253.last)
x = i8253.last - y;
else {
x = i8253.last + (0x10000 - y);
if (x > 3*MaxPeriod) {
outb(Tmode, Load2|Square);
outb(T2cntr, 0); /* low byte */
outb(T2cntr, 0); /* high byte */
y = 0xFFFF;
x = i8253.period;
}
}
i8253.last = y;
i8253.ticks += x>>1;
ticks = i8253.ticks;
iunlock(&i8253);
return ticks<<Tickshift;
}