PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq

Compute the number of ticks to wait to measure TSC frequency.
Instead of (ACPI_TIMER_FREQUENCY / 10000) = 357 and 357 * 10000 = 3570000,
use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
363 counts is a calibration time of 101.4 uS.

The idea comes from Michael and Paolo.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul A Lohr <paul.a.lohr@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
index e6fea231123d9740964fa24b08ba9bc8b92aec19..020031e3f4a53c62eb14db7c6e1e113b145e40c5 100644 (file)
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
@@ -340,13 +340,13 @@ GetTimeInNanoSecond (
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r

-  during a 100us period as determined by the ACPI timer. The ACPI timer is\r
-  used because it counts at a known frequency.\r
-  The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000\r
-  clocks of the ACPI timer, or 100us. The TSC is then sampled again. The\r
-  difference multiplied by 10000 is the TSC frequency. There will be a small\r
-  error because of the overhead of reading the ACPI timer. An attempt is\r
-  made to determine and compensate for this error.\r
+  during a 101.4 us period as determined by the ACPI timer.\r
+  The ACPI timer is used because it counts at a known frequency.\r
+  The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r
+  or 101.4 us. The TSC is then sampled again. The difference multiplied by\r
+  9861 is the TSC frequency. There will be a small error because of the\r
+  overhead of reading the ACPI timer. An attempt is made to determine and\r
+  compensate for this error.\r

 \r
   @return The number of TSC counts per second.\r
 \r
 \r
   @return The number of TSC counts per second.\r
 \r


@@ -366,22 +366,28 @@ InternalCalculateTscFrequency (
   InterruptState = SaveAndDisableInterrupts ();\r
 \r
   TimerAddr = InternalAcpiGetAcpiTimerIoPort ();\r
   InterruptState = SaveAndDisableInterrupts ();\r
 \r
   TimerAddr = InternalAcpiGetAcpiTimerIoPort ();\r

-  Ticks = IoRead32 (TimerAddr) + (ACPI_TIMER_FREQUENCY / 10000);    // Set Ticks to 100us in the future\r
+  //\r
+  // Compute the number of ticks to wait to measure TSC frequency.\r
+  // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.\r
+  // 363 counts is a calibration time of 101.4 uS.\r
+  //\r
+  Ticks = IoRead32 (TimerAddr) + 363;\r

 \r
   StartTSC = AsmReadTsc ();                                         // Get base value for the TSC\r
   //\r
 \r
   StartTSC = AsmReadTsc ();                                         // Get base value for the TSC\r
   //\r

-  // Wait until the ACPI timer has counted 100us.\r
+  // Wait until the ACPI timer has counted 101.4 us.\r

   // Timer wrap-arounds are handled correctly by this function.\r
   // Timer wrap-arounds are handled correctly by this function.\r

-  // When the current ACPI timer value is greater than 'Ticks', the while loop will exit.\r
+  // When the current ACPI timer value is greater than 'Ticks',\r
+  // the while loop will exit.\r

   //\r
   while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {\r
     CpuPause();\r
   }\r
   //\r
   while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {\r
     CpuPause();\r
   }\r

-  EndTSC = AsmReadTsc ();                                           // TSC value 100us later\r
+  EndTSC = AsmReadTsc ();                                           // TSC value 101.4 us later\r

 \r
   TscFrequency = MultU64x32 (\r
 \r
   TscFrequency = MultU64x32 (\r

-                   (EndTSC - StartTSC),                             // Number of TSC counts in 100us\r
-                   10000                                            // Number of 100us in a second\r
+                   (EndTSC - StartTSC),                             // Number of TSC counts in 101.4 us\r
+                   9861                                             // Number of 101.4 us in a second\r

                    );\r
 \r
   SetInterruptState (InterruptState);\r
                    );\r
 \r
   SetInterruptState (InterruptState);\r

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
index 8819ebcfccef7446c88254b5c189052a3badfd64..29521f8b220b062541015318751cf38d0f373065 100644 (file)
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
@@ -20,13 +20,13 @@
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r

-  during a 100us period as determined by the ACPI timer. The ACPI timer is\r
-  used because it counts at a known frequency.\r
-  The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000\r
-  clocks of the ACPI timer, or 100us. The TSC is then sampled again. The\r
-  difference multiplied by 10000 is the TSC frequency. There will be a small\r
-  error because of the overhead of reading the ACPI timer. An attempt is\r
-  made to determine and compensate for this error.\r
+  during a 101.4 us period as determined by the ACPI timer.\r
+  The ACPI timer is used because it counts at a known frequency.\r
+  The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r
+  or 101.4 us. The TSC is then sampled again. The difference multiplied by\r
+  9861 is the TSC frequency. There will be a small error because of the\r
+  overhead of reading the ACPI timer. An attempt is made to determine and\r
+  compensate for this error.\r

 \r
   @return The number of TSC counts per second.\r
 \r
 \r
   @return The number of TSC counts per second.\r
 \r

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
index 7f7b0f8f62947712e3a3a3d66df51ddeece1c14a..b141c680fb823c59f08efd624d46a9731b3ff224 100644 (file)
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
@@ -20,13 +20,13 @@
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r
   Calculate TSC frequency.\r
 \r
   The TSC counting frequency is determined by comparing how far it counts\r

-  during a 100us period as determined by the ACPI timer. The ACPI timer is\r
-  used because it counts at a known frequency.\r
-  The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000\r
-  clocks of the ACPI timer, or 100us. The TSC is then sampled again. The\r
-  difference multiplied by 10000 is the TSC frequency. There will be a small\r
-  error because of the overhead of reading the ACPI timer. An attempt is\r
-  made to determine and compensate for this error.\r
+  during a 101.4 us period as determined by the ACPI timer.\r
+  The ACPI timer is used because it counts at a known frequency.\r
+  The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r
+  or 101.4 us. The TSC is then sampled again. The difference multiplied by\r
+  9861 is the TSC frequency. There will be a small error because of the\r
+  overhead of reading the ACPI timer. An attempt is made to determine and\r
+  compensate for this error.\r

 \r
   @return The number of TSC counts per second.\r
 \r
 \r
   @return The number of TSC counts per second.\r
 \r