[m5-dev] 8254 PIT (timer device) programming

[Gabe Black]

   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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