off topic: irq8 realtime clock

Calamar · Posted: Thu Jul 14, 2005 10:54 am

how much seconds are every irq8 interruption ??
it's a fixed interval for all PCs ?? or it depend from bios ??
I don't remember but I think it could be change right ??
Some tutorial ??
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Daniel H. Sagarra
La Plata (Argentina)

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

What is an irq8? I never heard of this one before.

Calamar · Posted: Thu Jul 14, 2005 12:08 pm

The output pulsesn of the real time clock is used as a pacing clock to generate interrupts on IRQ8
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Daniel H. Sagarra
La Plata (Argentina)

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

He is not talking about a PIC but rather a PC

Ttelmah · Guest

This is very off-topic, but the answer is that it does not depend on the BIOS, and is the same on every PC, _but changes with the OS_.
The hardware is the same (or has to _emulate_ the same behaviour) on all PC's, but the actual frequency is programmable, and will vary with the OS being used. It is (for example), different between W9x, and WXP. It is also different on specialist systems like 'NT embedded'.
You need to either look at the chip registers, or the paperwork for your OS, to find what frequency this interrupt will occur at.
It is normally 18.2 times/second on W9x.
Several existing programs may interfere with this. The old drivers for SoundBlaster cards, used to reprogram this interrupt, as do a number of other things that did accurate/fast timing. This was the reason for the clock 'drifting' when some programs were run in W9x. In NT, 2K, and XP, the internal clock is resynchronised to the RTC, at a more frequent interval, which helps correct this.
Generally it'd be more 'normal' to use higher level access to give clock information, which would include higher frequency events if required. Using this directly, is also not possible under protected mode OS's, without writing a ring0 driver.

Best Wishes

valemike · Guest

I googled irq8, and found that it is one of the PCI bus interrupt levels on a PC where the RTC resides. Other irqX levels include keyboard, com1, com2, mouse, etc.

http://www.aesystems.com/irq_map.html

Calamar · Posted: Fri Jul 15, 2005 10:11 pm

thank you valemike, Ttelmah and mark.
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)

mustafa yuce · Guest

mustafa yuce · Guest