Timer interrupts

Timer interrupts

[madprops]

Hi,

i'm using CP0_Count/CP0_Compare to get timer interrupts. They should be
turned off while being in kernel mode (performing syscalls / handling
tlb-misses etc) and enabled in user mode. 

Whenever a timer interrupt happens in kernel mode, the exception should be
delayed until it is switched back to the user. Up to now I set
CP0_Status(IE) to zero when entering the kernel. Does this allow pending
interrupts or are incoming interrupts totally ignored then ??

The problem that might arise (in the second case) is that CP0_Count reaches
and passes CP0_Compare while interrupts are turned off. Back in user mode,
the running user process would get an unacceptable excessive time slice.

Thanks,

Thomas





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Re: Timer interrupts

[Dominic Sweetman]

> i'm using CP0_Count/CP0_Compare to get timer interrupts. They should be
> turned off while being in kernel mode (performing syscalls / handling
> tlb-misses etc) and enabled in user mode. 

This isn't going to work.  The hardware does nothing to inhibit
interrupts in kernel mode, and the system depends on them (performance
would be truly dreadful if no interrupt could be taken in kernel mode).

The kernel is already using CP0_Status and Count/Compare for its own
purposes, which you will be breaking...

Whatever it is you were trying to do, you need to do some other way!

--
Dominic Sweetman
MIPS Technologies