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Old 07-23-2008, 09:18 AM   #1
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Making CLOCK_TICK_RATE a variable in linux

I am using linux 2.6.19, I want the CLOCK_TICK_RATE macro defined in asm-arm/arch-at91rm9200/timex.h as a variable, so that the board can work in different clock frequencies.
Is it possible to do , as many of the macros depend on the CLOCK_TICK_RATE macro.
If it is possible please tell me how to go about.

Old 07-23-2008, 09:36 AM   #2
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If you want different values for CLOCK_TICK_RATE, you will have to compile different kernels for each value. If you don't want to do that, Red Hat have figured out a way to pass a tick divider to the kernel on boot in RHEL 4.7 and 5.

Other than that, you probably should check out dynticks which is not in the 2.6.19 kernel (and may not be supportive of your arch yet) and forget about the tick rate altogether unless you have a very specific reason for either high or low tick rates.
Old 07-24-2008, 04:44 AM   #3
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Thanks jcookeman for reply.

I am using linux 2.6.19 and a RFS for the Atmel sam920.
I have been able to change the u-boot 1.1.5 to support the variable clock frequency under which the board can work.

if the board is having is having 80MHz , then the kernel automaticallly takes care of working in 80MHz.
and the CLOCK_TICK_RATE in the include/asm-arm/arch-at91rm9200/timex.h has to be updated accordingly.

if the boards frequency changes to 150Mhz, then the kernel automatically takes care of working in 150MHz.
and the CLOCK_TICK_RATE in the include/asm-arm/arch-at91rm9200/timex.h need not to be updated, for the kernel to work properly. But only the date command does not work properly, as there will be drift in the seconds increment of the date command.

this can be adjusted using adjtimex .Is there a way to tell adjtimex the amount of tick , tolerance to be adjusted in accordance with the new board frequency( for 80mhz to 150Mhz ) .

Thanks for help


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