Microros baudrate issue103

[PaulBouchier]

This PR closes Issue #103 where the pico runs 115200 baud rate, and the default is 115200 if not specified. This would cause a mismatch after linorobot2 PR #174 is merged. The baud rate for all microcontrollers is set to 921600.

The README.md is updated to give an overview of this repo and to advise when using this repo is appropriate, and to note its coupling to the Jazzy branch of linorobot2, and to point to the hippo5329 repo for new users. This advice should be good until most of the goodness in the hippo5392 repos are migrated to this upstream repo.

This PR is tied to linorobot/linorobot2#176

Please merge this and the associated linorobot2 PR at the same time, to avoid inconsistent repos.

[grassjelly]

does changing to this new default baud rate work on Teensy 3.1/3.2?

[PaulBouchier]

According to this: https://www.pjrc.com/teensy/td_uart.html the manufacturer PJRC says Teensy 3.2 can go up to 4.8Mb/s. According to this: https://forum.pjrc.com/index.php?threads/teensy-3-1-max-baud-rate.29400/ back in 2015 someone said they'd done a fair bit of testing around 1Mb/s.
So I think the answer would be it should work, but I haven't tested it.

Your question begs the question, "what should our test matrix be?" Or, what hardware configs should we test before releasing an update. I'm open to your view on this, but you don't have any HW, right? I have pico and ESP32 but not Teensy. The statement in the README about Teensy being legacy is essentially a "not tested" disclaimer. I think the same kind of question will arise with all the flavors of lidar and IMU. You've probably heard the saying, "if it's not tested, it's broken". I guess at one time all these things were tested by someone, but at this point we probably have to wait for issues to be raised to know if something we don't test doesn't work.

Thoughts?

[grassjelly]

thanks @PaulBouchier . I'm okay with the changes. LGTM. Could we add a deprecation notice in the README.md about this change, and perhaps this PR as well just to point out the decision changes. This is just to guide users who might rebuild their robots and still in the Teensy series.

[PaulBouchier]

Great! Thanks. Yes I'll push an update to README momentarily. It will have wording like this:

Teensy support deprecated

The last versions of the Teensy microcontroller family (4.0 and 4.1) were introduced in 2019 and 2020. The owner, PJRC, has transferred the design to Sparkfun and there will be no more Teensy models. This version of linorobot2_hardware should support the Teensy family of microcontrollers as it used to - support has not been removed - but Teensy is untested on this version and the Teensy family should be considered deprecated. Problems may not be fixed. This version of firmware changes the default baud rate for a serial connection to the microcontroller to 921600 baud. Specs indicate the Teensy 3.2 and later should support that baud rate but this version of linorobot2_hardware has not been tested with any of the Teensy miicrocontrollers.

If someone in the linorobot2 community really feels Teensy should get continuing support, they are welcome to come forward and test it and contribute fixes to anything that breaks.