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Forum Topic - dynamic cpu clock speed and QNX:

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Josh Schmiedlin(deleted)

09/19/2008 3:07 PM

post13720

Hi I'm running QNX 6.3.2 and was wondering if there were any sort of gotcha's or things to look out for if I were to 
change the core clock speed of the processor.   I have attempted this in the past (moving from a high clock rate to a 
significantly lower one, ~20 MHz) and it seemed (sorry I don't have any solid numbers) that QNX was very very slow to 
respond to just about everything including typing on the terminal.

I was just wondering if there if anyone has experience with this sort of issue and if QNX supports dynamic clock rate 
changes.

Thanks,

Josh

Colin Burgess(deleted)

09/19/2008 3:15 PM

post13721

Re: dynamic cpu clock speed and QNX

We don't support it.

Josh Schmiedlin wrote:
> Hi I'm running QNX 6.3.2 and was wondering if there were any sort of gotcha's or things to look out for if I were to 
change the core clock speed of the processor.   I have attempted this in the past (moving from a high clock rate to a 
significantly lower one, ~20 MHz) and it seemed (sorry I don't have any solid numbers) that QNX was very very slow to 
respond to just about everything including typing on the terminal.
> 
> I was just wondering if there if anyone has experience with this sort of issue and if QNX supports dynamic clock rate 
changes.
> 
> Thanks,
> 
> Josh
> 
> _______________________________________________
> OSTech
> http://community.qnx.com/sf/go/post13720
> 

-- 
cburgess@qnx.com

Josh Schmiedlin(deleted)

09/25/2008 12:06 PM

post14035

Re: dynamic cpu clock speed and QNX

Is there any plans for future support of this?

Would you be able to point me to something specific in the kernal/ipl/etc that is based on cpu clock cycles rather than 
actual time?  And if so is there a way to modify these values after the system is booted?

Thanks,

Josh

Colin Burgess(deleted)

09/25/2008 12:51 PM

post14038

Re: dynamic cpu clock speed and QNX

Josh Schmiedlin wrote:
> Is there any plans for future support of this?

Not that I'm currently aware of.

> Would you be able to point me to something specific in the kernal/ipl/etc that is based on cpu clock cycles rather 
than actual time?  And if so is there a way to modify these values after the system is booted?

The nanospin routines would need it (affecting many drivers).  cycles_per_sec in qtime would need to be adjusted, as 
would other qtime values.

The kernel trace module would have to be notified of the frequency change - this would invalidate the header that 
tracelogger wrote.  The IDE's SystemProfiler plugin would also need to be
updated.

Adaptive partitioning uses ClockCycles for microbilling.

Many systems assume that ClockCycles() is synchronised across CPUs, and increments at the same rate.

The profiling libs would need to be udpated too.

So not a trivial job, although doable.  It might be advisable to switch ClockCycles to another timer (such as an APIC 
timer) if this course would be pursued.

Do you have a specific business requirement for this?  You might be able to convince the powers that be that it makes 
sense if you have a good opportunity. :-)

> Thanks,
> 
> Josh
> 
> _______________________________________________
> OSTech
> http://community.qnx.com/sf/go/post14035
> 

-- 
cburgess@qnx.com

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