How to "activate" the isr for PWMs?

Question

The isr still doesn't trigger on the PWM cycle. I guess I need to set bits 1 and 2 of register PWL0R to some non-zero value to give the isr a priority (if those bits are 0 the isr is disabled). What is the best way to do that. It seems that the WrPortI(PWL0R, NULL, 0x02) command should work, but I can't read back that register and when I use the WrPortI function to write the value the debug connection will drop out.

Answer 1

You might want to look at code in Lib/Rabbit4000/Peripherals/PWM.LIB. In particular, pwm_set() looks like it will configure PWL0R with an interrupt priority.

Since you can't read back the PWL0R register, you'd use the address its "shadow" register (&PWL0RShadow) as the second parameter to WrPortI(). So something like:

// set ISR priority
WrPortI(PWL0R, &PWL0RShadow, PWL0RShadow | 0x02);

You could also use BitWrPortI() to change a single bit.

Edit: That answer covers Dynamic C 10 and the Rabbit 4000 or later. The pwm_set() function in Dynamic C 9 doesn't allow setting an interrupt level because the original Rabbit 3000 didn't have that feature. You may be able to copy some of the pwm_set() code from Dynamic C 10 for use within Dynamic C 9.

https://github.com/digidotcom/DCRabbit_10/blob/master/Lib/Rabbit4000/Peripherals/PWM.LIB

Make sure your board has a Rabbit 3000A processor (UL2T or UZ2T marking instead of IL1T/IZ1T). I'd think that anything sold in the last 15 years would have the old revision 0 version of the 3000 chip.

Comments

Note that I've added additional information in the response to your support case.

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I did dig down into the R3000.lib and found that the pwm_set() command will write over the entire PWL0R with only one possible option on bit 0 for "spreading".  This effectively disables the ISR priorities every time it is used.
I copied that and added an |= 0x02 to the byte being written to PWL0R.  That works, but now when that is executed the code will stop working.  Even if I don't set the vector.
Could it be that the priority should be 2 or 3 instead of 1?