ArmPkg/TimerDxe: Changed calculation to allow 1KHz granularity frequency

Prior to this change the frequency was rounded to 1Mhz.
This change rounds the timer frequency to 1KHz.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15921 6f19259b-4bc3-4df7-8a09-765794883524

ArmPkg/Drivers/TimerDxe/TimerDxe.c

@@ -141,12 +141,13 @@ TimerDriverSetTimerPeriod (
   ArmArchTimerDisableTimer ();
 
   if (TimerPeriod != 0) {
-    // Convert TimerPeriod to micro sec units
-    TimerTicks = DivU64x32 (TimerPeriod, 10);
+    // TimerTicks = TimerPeriod in 1ms unit x Frequency.10^-3
+    //            = TimerPeriod.10^-4 x Frequency.10^-3
+    //            = (TimerPeriod x Frequency) x 10^-7
+    TimerTicks = MultU64x32 (TimerPeriod, FixedPcdGet32 (PcdArmArchTimerFreqInHz));
+    TimerTicks = DivU64x32 (TimerTicks, 10000000U);
 
-    TimerTicks = MultU64x32 (TimerTicks, (PcdGet32(PcdArmArchTimerFreqInHz)/1000000));
-
-    ArmArchTimerSetTimerVal((UINTN)TimerTicks);
+    ArmArchTimerSetTimerVal ((UINTN)TimerTicks);
 
     // Enable the timer
     ArmArchTimerEnableTimer ();

ArmPkg/Library/ArmArchTimerLib/ArmArchTimerLib.c

@@ -82,8 +82,10 @@ MicroSecondDelay (
   UINT64 TimerTicks64;
   UINT64 SystemCounterVal;
 
-  // Calculate counter ticks that can represent requested delay
-  TimerTicks64 = MultU64x32 (MicroSeconds, TICKS_PER_MICRO_SEC);
+  // Calculate counter ticks that can represent requested delay:
+  //  = MicroSeconds x TICKS_PER_MICRO_SEC
+  //  = MicroSeconds x Frequency.10^-6
+  TimerTicks64 = (MicroSeconds * PcdGet32 (PcdArmArchTimerFreqInHz)) / 1000000U;
 
   // Read System Counter value
   SystemCounterVal = ArmArchTimerGetSystemCount ();