PPC440 hangs after first interrupt

The thing is really odd. I wanted to figure out when the program jumps to the address 0x60. I used XMD, set a breakpoint to the interrupt and went through the whole interrupt stuff step by step (i.e. instruction by instruction). I could see, that the program is continued correctly after the interrupt (it sends data through UART). So everything worked as expected! However, when I then use "con" to continue the program (after the interrupt was successful and the normal program already continued), the program freezes again and the program counter is set to 0x60 (which seems to be a program exception or something like that).

How can that be?

Matthias

Just a small update again. I managed to get the design working a bit better... I modified my linker script, such that the .vectors section is now stored in the BRAM memory instead of the DDR2 memory. As a result the processor keeps working after an interrupt. So maybe the problem was some kind of timeout error because of the slow DDR-RAM?

But I now have the problem that the processer seems to see interrupts all the time. Actually there are no interrupts from the interrupt controller. So the processor just stays in the interrupt routines for an external interrupt all the time and the normal program is never continued after there was one or more real interrupts. But it is now possible to have more than just a single interrupt.

The odd thing again is that the processor goes to the normal program when I use step by step in XMD.

Matthias

Matthias Alles schrieb:

I found that catching interrupts when debugging is very hard to do. I had the same problem of missing interrupts when trying to write the stack frame save code for a RTOS that I wrote. I was using the PPC405 though.

---Matthew Hicks

I found the solution for this problem. The thing is that the flag for a decrementer interrupt (DEC) was set in the timer status register (TSR) after powerup. Since I don't use this DEC interrupts the flag of course is never cleared. Now when I enable my external interrupts (EE flag in MSR) the DEC interrupt is enabled as well. Since I don't have an interrupt handler for this case the interrupt occurs all the time and the normal program is never executed anymore. So a single line in the startup code does the trick:

XTime_TSRClearStatusBits(XREG_TSR_CLEAR_ALL);

The difference between stp and con in XMD seems to show that stp just doesn't care about interrupts at all.

Matthias