Re: L4 interrupt association

[Peter 'p2' De Schrijver]

On Wed, May 14, 2003 at 12:36:53PM +0200, Volkmar Uhlig wrote:
> > -----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.
> 

Yep. L4Ka::Pistachio on IA32.

> 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.
> 

Ok. IC.

> 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.
> 

Oh, does the SystemClock give me the wall clock time then ? I was under the
impression SystemClock gives me the time passed since system boot.

Thanks,

p2.