1 files changed, 314 insertions, 0 deletions
diff --git a/os/pc/i8253.c b/os/pc/i8253.c
new file mode 100644
index 00000000..d7cff39e
--- /dev/null
+++ b/os/pc/i8253.c
@@ -0,0 +1,314 @@
+#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 > (4*MaxPeriod)/5)	/* strong attraction to 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 = i8253.hz;
+
+	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;
+}
+
+void
+delay(int millisecs)
+{
+	millisecs *= m->loopconst;
+	if(millisecs <= 0)
+		millisecs = 1;
+	aamloop(millisecs);
+}
+
+void
+microdelay(int microsecs)
+{
+	microsecs *= m->loopconst;
+	microsecs /= 1000;
+	if(microsecs <= 0)
+		microsecs = 1;
+	aamloop(microsecs);
+}
+
+/*  
+ *  performance measurement ticks.  must be low overhead.
+ *  doesn't have to count over a second.
+ */
+ulong
+perfticks(void)
+{
+	uvlong x;
+
+	if(m->havetsc)
+		cycles(&x);
+	else
+		x = 0;
+	return x;
+}