minor lora sx126x _cmd optimization

[maholli]

Currently, the micropython-lib lora sx126x driver dynamically creates at least one, sometimes two, memoryview objects with each call to _cmd. This PR simply provides the class with a long-lived memoryview object for _cmd to easily slice as necessary.

Unlike the SX127x chips, Semtech unfortunately designed the SX126x modems to be more command-centric (as opposed to directly setting registers). Given the amount _cmd is called during normal device operation, even a minor improvement here should have a decent impact.

Basic TX and RX tests pass on hardware.

@projectgus, care to review?

[projectgus]

Thanks for noticing this and submitting a fix, @maholli!

The other thing to change is micropython/lora/lora-sx126x/manifest.py. Please bump the version from 0.1.2 to 0.1.3 so that clients will update.

I have a suggestion for a further change inline, too.

The CI is also failing on the commit message format. To make CI happy, make any code changes changes then run commit --amend to change the existing commit contents and also rewrite the message to match the project format. After this you can git push --force back to your branch on GitHub in order to update.

For more details see:

• https://github.com/micropython/micropython-lib/blob/master/CONTRIBUTING.md#pull-requests
• https://github.com/jimmo/git-and-micropython#README

[maholli]

Requested changes have been made and the checks are happy. Let me know if there's anything else. Thanks again, @projectgus.

[projectgus]

Looks good to me, thanks @maholli. I would probably squash the two commits into one, but we can probably also do that when we merge this.

[maholli]

Looks good to me, thanks @maholli. I would probably squash the two commits into one, but we can probably also do that when we merge this.

@projectgus Yes, feel free to squash when you merge. Thanks again!

[dpgeorge]

Thanks for the contribution. Squashed and merged in 60d1370