Timing questions

boo_matic · 02-29-2008, 07:57 AM

Hello,

I was reading a bit about kernel hacking and module programming. I read an o'reilly book about it, etc...

I was wondering if I understand this right. Is it true I can't sleep for some time that's smaller than one jiffy, 4ms? I know there's udelay and mdelay, but busy waiting isn't really an option for me.

Or are there any other options?

sundialsvcs · 03-02-2008, 04:10 PM

Linux is not a real-time operating system (RTOS). If you need more precise timing than that, you're going to need to be looking at other alternatives.

Which (even within Linux) do exist! What is most appropriate for your application depends upon ... your application.

P.S. You cannot "busy wait" in the kernel. For very obvious reasons . . .

boo_matic · 03-02-2008, 11:19 PM

Thank you for your reply.

No busy-wait? I read about udelay and mdelay in an o'reilly book, they said this would be busy-waiting.

Can you tell me something about the alternatives within linux?

sundialsvcs · 03-03-2008, 08:44 PM

What are you trying to do?

What is the requirement that is prompting you to explore in this direction?

boo_matic · 03-04-2008, 10:32 AM

Well,
at the moment out of curiosity, because it's interesting. I'm just trying to understand linux a bit better.

Originally I was researching some ways to send DMX with an embedded linux device, open source, not for profit. But I think I'll do this with it's uart, which fortunately can be clocked at exactly 250kbit. But there's still one moment where I need to send a 88us break.

sundialsvcs · 03-04-2008, 09:00 PM

That's what you should use: a UART; a hardware-device that can be programmed to issue an external signal or an interrupt after a precisely controllable interval.

Linux can field at-least a "bottom half" response to a hardware interrupt "speedily," but it does not guarantee the interrupt-latency nor does it guarantee the additional latency inherent in scheduling the "upper half" (by any other name). This is not within the design scope of this operating-system.