Tutorial example output anomaly using low level access PPI on MDBT42Q breakout board

Tue 2020.03.17

Spent yesterday toying with Low Level Access on STM32 using a Pico. All went well, but not all the functionality appears to be available as with the nRF52LL

So, this morning, after heeding this note:

** Real time counter
You should only set on ch2 as 0 and 1 are used by Espruino/Bluetooth

I modifed the toggle channel to 4 and the enable channel to 3. Now the setWatch can be added without killing the underlying PPI counter. But, the setWatch never detects a pulse that clearly swings both rails.

That is, until during code cleanup to post to the forum, I failed to remove a commented out line of code within the setInterval initialization that caused a separate function to execute unintentionally.
It contains a local scope copy of the toggle command, (and now I see the global scope one also) but isn't really needed. Why it allows PPI and setWatch to play together is still a bit of a mystery, but at least I have a stable, repeatable, reloadable after power up chunk to play with.

There is also another anomaly, that when specifying 'af_output' using pinMode, that after PPI signal is sent to the external LED, that the mode changes from 'af_output' to just 'output' with no intentional change by me. (maybe this is why this code block now appears to be stable? - but don't we need the special 'af_' prefix as we are using PPI?)

While I continue to play/learn how all the bits work under the hood, the following still needs review:

• The flipped buttons in post #5
  
• What channel setWatch is using that may conflict with PPI channels
  
• The prescaler code that limits the counter frequency post #11
  
• Inadvetent pinMode change 'af_output' to just 'output'
  
• Review reset(1) to stop underlying PPI post #10
  
• Requirement to force a hard counter stop when making a setup change
  
  

When playing with this code file, be aware it takes around five seconds to upload and initialize before commands may be entered.

1 Attachment

• codeNRF52LLPPI20200317Forum.js