MeasureTicks.c

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#include "../OcCpuInternals.h"
 
#include <Library/BaseLib.h>
#include <Library/IoLib.h>
 
VOID
EFIAPI
AsmMeasureTicks (
  IN  UINT32  AcpiTicksDuration,
  IN  UINT16  TimerAddr,
  OUT UINT32  *AcpiTicksDelta,
  OUT UINT64  *TscTicksDelta
  )
{
  UINT32  AcpiTick0;
  UINT32  AcpiTick1;
  UINT32  AcpiCurrentDelta;
  UINT64  Tsc0;
  UINT64  Tsc1;
 
  AcpiTick0 = IoRead32 (TimerAddr);
  Tsc0      = AsmReadTsc ();
 
  do {
    CpuPause ();
 
    //
    // Check how many AcpiTicks have passed since we started.
    //
    AcpiTick1 = IoRead32 (TimerAddr);
 
    if (AcpiTick0 <= AcpiTick1) {
      //
      // No overflow.
      //
      AcpiCurrentDelta = AcpiTick1 - AcpiTick0;
    } else if (AcpiTick0 - AcpiTick1 <= 0x00FFFFFF) {
      //
      // Overflow, 24-bit timer.
      //
      AcpiCurrentDelta = 0x00FFFFFF - AcpiTick0 + AcpiTick1;
    } else {
      //
      // Overflow, 32-bit timer.
      //
      AcpiCurrentDelta = MAX_UINT32 - AcpiTick0 + AcpiTick1;
    }
 
    //
    // Keep checking AcpiTicks until target is reached.
    //
  } while (AcpiCurrentDelta < AcpiTicksDuration);
 
  Tsc1 = AsmReadTsc ();
 
  //
  // On some systems we may end up waiting for notably longer than 100ms,
  // despite disabling all events. Divide by actual time passed as suggested
  // by asava's Clover patch r2668.
  //
  *TscTicksDelta  = Tsc1 - Tsc0;
  *AcpiTicksDelta = AcpiCurrentDelta;
}