I imagine it's both, and implementation dependent if an interrupt
occurs when the PIT timer expires, but it's been a long time. I
imagine the datasheet for at 8254 timer would be a good place to start.
Ali
On May 24, 2008, at 5:40 AM, Gabe Black wrote:
I'm at a point now where the kernel is trying to wait for the 8254
timer to tick 300 times before moving to the local APIC timer to use
for timer interrupts. As we determined before, the 8254 is the same
as the PIT used in Alpha Tsunami, so I'm going to move the Alpha
code to a neutral location and use it in x86 as well. What is the
event that the timer schedules? Is that a tick to update the
counter, or is that to fire the periodic interrupt? If it's the
former that seems really inefficient. If it's the later, then I'm a
little concerned that the way the timer is being programmed by the
OS isn't a factor in when it fires. That would especially be a
problem with the tickless kernel where the timer interrupt doesn't
happen all the time. I would imagine that has to happen by
programming the timer not to go off for a while until it actually
needs to.
Gabe
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