RE: L4 interrupt association

[Volkmar Uhlig]

> -----Original Message-----
> From: Peter 'p2' De Schrijver [mailto:address@hidden 
> Sent: Tuesday, May 13, 2003 11:51 PM
> 
> I'm playing around with associating IRQs. I can't associate 
> IRQ 8 (RTC) though. This would be useful to accurately read 
> the RTC. (Ie. use the RTC update interrupt to read the current 
> time). Associating other IRQs does seem to work.
> I tried IRQ 4 (UART 0) and that works fine. Any comments ? 
> Does L4 use the RTC IRQ for it's own purposes ?

Firstly, I assume you are talking about L4Ka::Pistachio on ia32. 
Note, that L4 exists in different APIs (V2, X0, X2/V4) and multiple
implementations (L4Ka::Pistachio, L4Ka::Hazelnut, FIASCO, L4/MIPS,
L4/Alpha, L4/x86) for many architectures (IA32, IA64, ARM, MIPS, Alpha,
PPC). It is not always obvious about what kernel version and what
architecture you are talking about.

On IA32 systems without a local APIC the RTC is used as the time base
for timer ticks. Therefore, you can't associate the IRQ externally. On
systems with APIC the more accurate local APIC timer is used.

I do not think it makes sense to use the RTC timer in the first place,
since L4/X2 provides you an accurate time base using the SystemClock
syscall which also respects processor frequency changes etc and is
extremely cheap.  This also makes the code portable over different
hardware platforms.

- Volkmar