How to correctly disable MPC5646C eMIOS channels temporarily?

[mbu2015]

Hello All,

in my project I need to disable eMIOS channels temporarily.

I have to generate arbitrary pulses. I setup a SAOC channel fed by timer bus A with the compare value and set EDPOL to 1 to generate the rising edge.

Then in the channel interrupt I clear EDPOL and setup the compare value for the falling edge.

If I leave the channel active additional compare interrupts occur (as expected) which I have to avoid because the output period can be longer than the timebase period.

How do I prevent these needless compare IRQs from occuring?

I tried the following things without success:

1.) Clear UCPREN / set FEN in the interrupt after the falling edge: No effect

2.) Clear FEN / set UCPREN after falling edge: Only every other edge occurs at all (even worse)

3.) Clear both UCPREN+FEN: Same as 2.)

4.) Setting corresponding bit in EMIOSUCDIS breaks the whole system. Somehow the IRQ request does not go away by its own and contineous interrupts occur.

Touching EMIOSMCR.GPREN is not an option I think, as the eMIOS module itself has to operate contineously.

What is my misconception on channel deactivation? Are there timing constraints I'm not aware of?

With best regards

Matthias Busch

[PetrS · Accepted solution]

Hi,

If just interrupt have to be deactivated it is enough to clear the FEN bit. Then once the FLAG is set on next match the interrupt is not generated, unless FEN is set again and FLAG is set.

UCPREN disable clock to the channel internal counter so if Timer Bus A is used it makes no sense.

BTW you can easily use the DAOC mode to generate arbitrary pulse. But this mode is supported only on Type G and H channels.

BR, Petr

[mbu2015]

Hello Petr,

Thanks for your response.

The reason why clearing FEN alone was not sufficient was that I had to clear all flags in the CSR prior to setting FEN initially.

By doing so everything is fine now!

Best regards

Matthias