[ECOS] DSR stops running after heavy interrupts.

Joe Porthouse jporthouse@toptech.com
Wed Apr 5 21:09:00 GMT 2006

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.

	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

        // 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?

Many thanks,
Joe Porthouse
Toptech Systems, Inc.

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