sht3x: use periodic report mode

[nefelim4ag]

SHT3X supports periodic mode, which allows us to completely skip the "write" phase and wait, and just read data in one command.

Also, I corrected reactor pauses to the right numeric order (they are also wrong in htu21.py).

Thanks.

[JamesH1978]

Thank you for submitting a PR, pleas refer to point 3 in "What to expect in a review" in https://github.com/Klipper3d/klipper/blob/master/docs/CONTRIBUTING.md and provide a signed off by line.

Thanks
James

[KevinOConnor]

Thanks. Happy to commit this when you are ready.

Note, though, that host based pause() commands do not enforce a chip delay. The i2c_write() commands are queued and sent to the mcu for execution - pausing between queuing of commands does not ensure the mcu will have a pause between execution of commands.

There are a variety of ways to fix this. I'd guess the simplest would be to add an i2c_write_wait_ack() to bus.py (that uses self.i2c_write_cmd.send_wait_ack()). I'm not entirely sure what the sht3x chip requirements are though.

-Kevin

[nefelim4ag]

I'm not an experienced embedded developer, so I write pauses according to the datasheet with some additional sane margin "just in case".

In HTU code they all look like x10 of max datasheet values, maybe because reactor pause does not guarantee timings?
So, Initially, without complete understanding, I used the same order of values.
(like 20ms = 0.20, instead of 0.020)

With that said:

• If you would like, I can add and test wait_ack for i2c here, and after for some bme sensors, because I also have them (in separate PR if their timing differs as here). It looks like wait_ack should not cause issues, only a little overhead.
• Or, I can return pauses to x10 of max values and leave everything as is.

Thanks

[KevinOConnor]

Thanks. I committed this change.

The pause() timing is accurate - I'd guess that other code exaggerates delays to try to account for host delays not easily correlating to mcu delays. If you can make and test fixes for the bme code then that would be great.

-Kevin