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1 us delay generation

Note: This was originally posted on 11th May 2011 at http://forums.arm.com

Dear all,

I am using Linux OS with arm-elf tool chain. I am not able to generate 1 us delay using 'for loop' method of 'C' programming language.Is there anything that i can try?

thanks & regards
Avadhoot

Jerry Fan over 12 years ago

Note: This was originally posted on 11th May 2011 at http://forums.arm.com

sleep() can be used to get delay, but the accuracy is poor, almost 1ms, that is the tick of the linux system. So 1us can not be got by sleep() Cycle conter has a much high accuracy, that is the 1/CPU_freq. But the problem is that if "WFI" was used, for example, the idle task may use that instruction in some RTOS, the CPU will suspend, that is the cycle conter was supend. If "WFI" instruction was not used in Linux, cycle counter is a good way to delay 1us. I think some system API can be called to do that.
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Etienne SOBOLE over 12 years ago

Note: This was originally posted on 11th May 2011 at http://forums.arm.com

Maybe you could use the Cycle Counter Register

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0344b/Bgbjjhaj.html

I never succed to use it, maybe you'll have more chance !
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Martin Weidmann over 12 years ago

Note: This was originally posted on 11th May 2011 at http://forums.arm.com

Generating a reliable delay of a given length using a loop is difficult with modern processors, doubly so when running under a rich OS such as Linux. There is just so much going on you don't have control over.

Not done much Linux app development, but can't you use some sort of wait()/sleep() call from the OS?
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Marcus Harnisch over 12 years ago

Note: This was originally posted on 12th May 2011 at http://forums.arm.com

Not sure if usleep(2) is precise enough.
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Marcus
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