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* Re-program the timer for each loop instead of waiting for it to wrap around.

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With that we will usually start right away without having to wait for the
  timer to be in the desired state, which removes roughly 116ms of spinning
  around for a normal calibration run.
* Read back the value once after programming. The delay this introduces
  accounts for the fact that the counter will only start counting down on the
  next clock cycle.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@41680 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Michael Lotz 2011-05-23 13:25:44 +00:00
parent 2d62c17d26
commit 7adc7269d8
1 changed files with 16 additions and 14 deletions
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30
src/system/boot/platform/bios_ia32/cpu.cpp
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@ -185,9 +185,22 @@ calibration_loop(uint8 desiredHighByte, uint8 channel, uint64& tscDelta,
double& conversionFactor, uint16& expired)
{
uint8 select = channel << PIT_SELECT_CHANNEL_SHIFT;
uint8 channelPort = PIT_CHANNEL_PORT_BASE + channel;
out8(select | PIT_ACCESS_LOW_THEN_HIGH_BYTE | PIT_MODE_RATE_GENERATOR
| PIT_BINARY_MODE, PIT_CONTROL);
// Wait for the PIT to arrive at our starting position (high byte == 0xff)
// Fill in count of 0xffff, low then high byte
uint8 channelPort = PIT_CHANNEL_PORT_BASE + channel;
out8(0xff, channelPort);
out8(0xff, channelPort);
// Read the count back once to delay the start. This ensures that we've
// waited long enough for the counter to actually start counting down, as
// this only happens on the next clock cycle after reload.
in8(channelPort);
in8(channelPort);
// We're expecting the PIT to be at the starting position (high byte 0xff)
// as we just programmed it, but if it isn't we wait for it to wrap.
uint8 startLow;
uint8 startHigh;
do {
@ -221,26 +234,15 @@ static void
calculate_cpu_conversion_factor()
{
uint8 channel = 0;
uint8 channelPort = PIT_CHANNEL_PORT_BASE + channel;
uint8 control;
// When using channel 2, enable the input and disable the speaker.
if (channel == 2) {
control = in8(PIT_CHANNEL_2_CONTROL);
uint8 control = in8(PIT_CHANNEL_2_CONTROL);
control &= PIT_CHANNEL_2_SPEAKER_OFF_MASK;
control |= PIT_CHANNEL_2_GATE_HIGH;
out8(control, PIT_CHANNEL_2_CONTROL);
}
uint8 select = channel << PIT_SELECT_CHANNEL_SHIFT;
control = select | PIT_ACCESS_LOW_THEN_HIGH_BYTE | PIT_MODE_RATE_GENERATOR
| PIT_BINARY_MODE;
out8(control, PIT_CONTROL);
// Fill in count of 0xffff, low then high byte
out8(0xff, channelPort);
out8(0xff, channelPort);
uint64 tscDeltaQuick, tscDeltaSlower, tscDeltaSlow;
double conversionFactorQuick, conversionFactorSlower, conversionFactorSlow;
uint16 expired;