ESP32-S2 I2C does not honor repeated-start (no stop) in API?

[ladyada]

hey @me-no-dev i verified someone trying an ESP32-S2 with an lc709203f and i am pretty sure that the issue is that when we ask for no-stop in uint8_t TwoWire::endTransmission(bool sendStop) its sending a stop anyways.

This is the correct I2C transaction to read the ID code (on avr chipset)

we write 0x11 register command to i2c device 0xB, don't stop, then read 3 bytes of data

if we run the same code on ESP32-S2 I get:

(there's a delay due to serial printf)
with wrong data 0xFF

if we go back to avr and turn ON stop (which is incorrect), we get the same resulting trace:

same wrong data

this could be the root cause for
#4589
#4561
#4375
#4403

those are also repeated-start devices. not all i2c devices require repeated start

[me-no-dev]

@ladyada sorry for the delay. I2C for S2 uses ESP-IDF's I2C driver. I did not find a way to ensure no-stop there and remember that in order for that to work, write and read need to happen in one bus transaction (not really Arduino-friendly and with possible multitasking issues). Unfortunately we have not heard from @stickbreaker in a loong time (he was maintaining the driver) but we are looking into getting some help internally to be able to handle that in near future.

[ladyada]

hihi thanks for replying - there's quite a few chips that require write-then-read in one no-stop transaction. we haven't heard of this problem before for ESP32 (just S2) so it could be a regression in v4.2 or for S2

either way its OK if there's a separate call just for write-then-read added, we have abstracted away the API for all our sensors so we could easily add that exception - just let me know :)

[erichiller]

Is there a surround workaround for this? Perhaps @ladyada you know of one?
I'm encountering this with:

• Adafruit ESP32-S2 Metro
• Adafruit MLX90640 (55°)

[ladyada]

there is no work-around, it must be fixed here/IDF :)

[me-no-dev]

we are aware of the issue, it will be fixed before 2.0.0 is released :)

[ladyada]

awesome thank you @me-no-dev :)

[VojtechBartoska]

This issue will be solved internally in ESP-IDF IDF-3460

[hallard]

ahah Just came up here after scratching my head for 2 hours trying to have battery monitoring on Metro ESP32 S2. Glad to see it's not on our side. Just let us know if there is a fixed branch to test before official release of 2.0.0

[SuGlider]

@ladyada , I just submitted a PR #5664 that shall fix the issue you reported.
Could you please apply it to your environment and verify if it solves this issue?

Thanks!

[ladyada]

@SuGlider LC709 works right now, so it seems to have solved at least that issue!

[me-no-dev]

Hi @ladyada could you please re-test with this new PR: #5683
I have only MLX90614 as sensor that requires repeated start and that worked without issues.

[nseidle]

I can confirm #5683 fixes the repeated start problem. Below is original bad recorded on ESP32-S2 w/ MLX90640:

Now with #5683 changes:

Sensor is happily reporting. Thanks @me-no-dev!