Reduce QTR PIO program size

[adamgreen]

I moved the initialization of the OSR, Y, and X registers from the start of the PIO program and put it into the QTRSensors.run() method before starting each sensor read. This reduced the size of the PIO code by 3 instructions.

NOTE: This change requires a more recent build of MicroPython which extends the rp2.StateMachine.exec() method to accept pre-encoded machine code. The commit which adds this functionality can now be found in this MicroPython master branch commit: https://github.com/micropython/micropython/commit/f9958417d8adb21147de776361a4414073cf7c77

[pdg137]

Hi! Thanks for this improvement. I finally merged it in https://github.com/pololu/pololu-3pi-2040-robot/commit/6ddb719da080c21d9d1fb03e9f92007a12848f24 (though that's a cherry-pick commit from the Zumo repo so it doesn't show up like a merge).

It seems to work but I would appreciate it if you could take a look too!

[adamgreen]

Ok. I will pull things together and test it on Friday.

[adamgreen]

Looks good to me:

• I code reviewed the merge and it matches my memory of the change I made last year.
• I upgraded the version of MicroPython running on my 3π+-2040 robot to Build 240117-9512cf9 micropython-pololu-3pi-2040-robot-v1.22.1-240117.uf2 This version includes the required PIO library change and matches what is currently recommended by the Pololu 3pi+ 2040 User's Guide
• I upgraded the python sources on the robot to match those in the master branch of this repository.
• I verified that the IR sensor samples ran as expected.

[pdg137]

Thank you for checking!