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Re: RM5231A: problems in timer using COUNT/COMPARE register.

To: Dinesh Nagpure <>
Subject: Re: RM5231A: problems in timer using COUNT/COMPARE register.
From: Dominic Sweetman <>
Date: Tue, 24 Sep 2002 09:40:49 +0100
In-reply-to: <AEC4671C8179D61194DE0002B328BDD2070C3F@ATLOPS>
Original-recipient: rfc822;
References: <AEC4671C8179D61194DE0002B328BDD2070C3F@ATLOPS>

> I am in the process of porting Linux to our FPGA platform using RM5231A
> processor. The COUNT/COMPARE register timer is acting funny with me. When I
> set the compare register value to something like 0x0100_0000 or less I get
> timer interrupt as expected but if I set the COMPARE register to a greater
> value timer interrupt never happens. I have verified this using our boot
> loader also and the results are the same. I am waiting for a reply from PMC
> but would also like to know if there is anyone out there who faced similar
> problems with RM5231A. From data sheets and user manual I know the count
> register is 32 bit but apparently there is some hitch somewhere that I need
> to discover. 

I'd be really surprised if there's a hardware bug; the RM5231A is an
old core and it always seemed to work.  Standard practice is to leave
COUNT free-running, and to get timer interrupts by setting COMPARE
ahead of it; this relies totally on being able to use the whole range
of values, and running seamlessly while COUNT overflows back to zero...

Unless you've already done a really low-level, nothing-else-running
software sanity check on this, it seems more likely that some piece of
software is periodically resetting COUNT, or changing COMPARE, behind
your back.

Dominic Sweetman
MIPS Technologies

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