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apic: fix lapic timer divider (fixes wrong lapic frequency on boot)

loading the divider before programming one shot mode *sometimes*
gives the wrong frequency. (X200s got 192Mhz vs. 266Mhz, after
5 boot attempts)

also reload the divider after programming periodic mode. (from
http://wiki.osdev.org/APIC_timer)

--- a/sys/src/9/pc/apic.c

+++ b/sys/src/9/pc/apic.c

@@ -124,6 +124,12 @@

 	lapicw(LapicTICR, lapictimer.max);

 	lapicw(LapicTIMER, LapicCLKIN|LapicPERIODIC|(VectorPIC+IrqTIMER));

+	/*

+	 * not strickly neccesary, but reported (osdev.org) to be

+	 * required for some machines.

+	 */

+	lapicw(LapicTDCR, lapictdxtab[lapictimer.tdx]);

+

 	lapicw(LapicTPR, 0);

 }

@@ -134,8 +140,8 @@

 lapictimerinit(void)

 {

 Retry:

-	lapicw(LapicTDCR, lapictdxtab[lapictimer.tdx]);

 	lapicw(LapicTIMER, ApicIMASK|LapicCLKIN|LapicONESHOT|(VectorPIC+IrqTIMER));

+	lapicw(LapicTDCR, lapictdxtab[lapictimer.tdx]);

 	if(lapictimer.hz == 0ULL){

 		uvlong x, v, hz;

-- 

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