[ECOS] DSR stops running after heavy interrupts.

[Stefan Sommerfeld]

Hi,

>> In a nutshell:
>> The real time clock DSR stops getting called after several minutes
>> of heavy UART ISR traffic.  I have been running into this on and off for 
>> a
>> while.  Lowering the serial ISR priority seems to help some, but not
>> eliminate the problem.
>>
>> Background:
>> Application is on a custom xScale PXA255 board without redboot.
>> When problem occurs the Real Time tick clock simply stops updating.  All
>> other aspects of the program seem to work correctly.  The real time ISR 
>> is
>> still getting called as well as other ISRs, but the real time clock DSR 
>> is
>> no longer called.
>>
>> In the Vectors.S file I can step through the execution and see what
>> is happening.  On return from the ISR the return code is examined to
>> determine if a DSR call should be added to the DSL list.  This check is 
>> done
>> here:
>>
>>         // The return value from the handler (in r0) will indicate 
>> whether a
>>
>>         // DSR is to be posted. Pass this together with a pointer to the
>>         // interrupt object we have just used to the interrupt tidy up
>>
>>         cmp     v1,#CYGNUM_HAL_INTERRUPT_NONE
>>         beq     17f
>>
>> When the problem occurs the branch (beq) is occurring that skips
>> adding the DSR to the list and ends the ISR.  I can see that R0 is 
>> correctly
>> 0x03 but the branch still occurs.  The problem may be in how this is 
>> getting
>> compiled.  In my JTAG tool I see the above code as:
>>
>> 00008C5C e3740001   CMN       R4,#00000001
>> 00008C60 0a000003   BEQ       00008c74
>>
>> Obviously there is some assembler substitution going on.  I'm not
>> sure why if the value is in r0, why v1 is being checked (not familiar 
>> with
>> the "v" register notation).  Also not sure why the resulting code refers 
>> to
>> R4.  R4 has a different value then R1 at this point in the execution.
>>
>> Any ideas on this?
>
> The fast that this works for a while and then breaks suggests it is
> something unusual going on.
>
> When the problem occurs take a look at the actually contents of memory
> which contains these instructions. Has it been corrupted? Be careful
> with your debugger here. If you just ask it to disassemble the code it
> might show you what is in the elf file, not what is in memory. Do a
> hex dump and compare the machine code bytes.

I had that experience too, not just with the uart (i'm using a PXA270). 
Currently using my FIFO DSRs it works better, but please do more research 
on that topic to fix this once and forever.

Bye...


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