decrementer exception(0x900).

[vbaradur]

This is with regard to POWEPC MPC 8555

We are observing the decrementer exception(0x900), resulting in board reboot

About Decrementer exception from datasheets
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The decrementer will cause an exception when it rolls over from all zeros to the LSB being set high again to begin the counting process.

My Question
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Wanted to check with you experts, that DECR should be loaded before the count reaching to 0x0000?

We are seeing this exception only now(one time occurence) from the history of last 10-15 years.

If you have more detail, can you please share

[r8070z]

Have a great day,

The MPC8555 has E500 core where decrementer interrupt can be disabled in the Timer Control Register (TCR[DIE]) even if external interrupt is enabled (MSR[EE] = 1). To avoid redundant decrementer interrupts, before reenabling MSR[EE], the interrupt handler must clear TSR[DIS] by writing a word to TSR using mtspr with a 1 in any bit position to be cleared and 0 in all others.
Details of the decrement operation you can find in section 9.4 Decrementer Operation of “EREF 2.0: A Programmer’s Reference Manual for Freescale Power Architecture Processors”
http://cache.freescale.com/files/32bit/doc/ref_manual/EREF_RM.pdf

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