I2CMini/Driver poor decode quality?

Breakout boards, sensors, other Adafruit kits, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
argonblue
 
Posts: 93
Joined: Wed Apr 25, 2012 12:18 am

I2CMini/Driver poor decode quality?

Post by argonblue »

Has anyone gotten reliably clean I2C decodes from an I2CMini or I2CDriver?

I recently bought an I2CMini (product ID 4970). It seems to work well enough as a USB-based I2C controller, but I can't get very clean decodes when I'm monitoring a live I2C bus.

Here is an example capture from running i2c.capture() using the Python API. The sampled I2C bus is on an Adafruit Clue running the Bluefruit demo.

Code: Select all

d4 20 SS7d!7f!0f 01 69!7d!28!SS59!S33!07!d5!d6 SP
d4 20 SS7d!7f!0f 01 69!7d!28!S35!3c!9c 3f S7a!P
38 28 S39 11 SS6c S39!SP
d4 20 Sd5 S6f!S10 27 c7!S65!cf!cc 6f 68 0f!SS15!P
d4 20 SS7d!7f!S10 27 S1f cb!9f!S30!bc!S00!SSS58 P
38 28 SSS3d!38!SS0c P
ee fa Sef 81 e7 d0!P
ee f7 Sef 57 f0 a0!P
d4 20 SSS3f!81 SS3e!9a SS3c!a4 3f S2c P
d4 20 Sd5 fa ff 05 02 S3e!9a SS3c!a4 3f S2c P
38 28 S39 S4f SS7a SS21!P
d4 20 Sd5 SS3f!SS00 SS5f S1f!SS3c!98 bf b0!SP
d4 20 Sd5 S4f!S40 SSS65!8f!c9 4f 66 2f!S58 98 P
38 28 S39 d6 S5c 43 S3c!86!P
d4 20 Sd5 SS3f!83!SS7d!S66 0f!cb!ef S4f!S6c P
d4 20 SS7d 7f!09!S39!3e!95 SSS1e cd S58 SP
d4 20 Sd5 S3f!S30 27 67!SS5f!93!1e cd 1f!58 SP
38 28 S39 f2 S57 b0!SSSP
d4 20 Sd5 S6f!e1!a0 4e 4f!65 8f!cc S33!57!S36 P
d4 20 SS7d!7f!0e!01 71 7d!2a 7f 61 SS57!S66!SP
38 28 S39 SS4f S57!c3 S08 07 P
88 24 00 P
89 S03!2a!c9 6f!68!P
I know this particular demo runs the I2C bus at 400kHz, but capturing a different demo (the Arcada full board test for the Clue) running at 100kHz doesn't give a much better decode. Note that the longer transactions starting with 0xD4 (7-bit address 0x6A, probably the LSM6DS33 IMU) decode especially poorly, with spurious NAKs and multiple repeated START conditions in a row.

I've tried multiple combinations of pullup resistor settings on the I2CMini, including none, and they don't seem to help.

Also, sigrok seems to have no problems decoding a similar capture. It doesn't detect spurious NAKs or START conditions. (I didn't set up a simultaneous capture, but I did capture the same bus running the same Clue demo. I did the capture at 2Msamp/s using an Adruino Micro running a custom logic analyzer sketch.)

Based on these experiences, I actively recommend not using I2CMini as an I2C bus analyzer or decoder. My understanding is that it shares hardware and firmware with the I2CDriver, so a similar warning might apply there.

I'm not going to ask for a refund, because the USB-based I2C controller functionality is still worth something to me. I would have been very disappointed to have bought the more expensive I2CDriver instead and to have discovered this sort of problem with it.

User avatar
mikeysklar
 
Posts: 13936
Joined: Mon Aug 01, 2016 8:10 pm

Re: I2CMini/Driver poor decode quality?

Post by mikeysklar »

@argonblue -

The GitHub repo for the i2cdriver has a number of open issues with several related to getting complete clean decodes without noise.

https://github.com/jamesbowman/i2cdriver/issues

Your feedback might be helpful for Excamera Labs to receive as they could have some suggestions?
Would you like to contact them?

[email protected]

User avatar
argonblue
 
Posts: 93
Joined: Wed Apr 25, 2012 12:18 am

Re: I2CMini/Driver poor decode quality?

Post by argonblue »

Thanks. I remember looking at that repository before and not seeing anything helpful. It has a lot of open issues, many of which have been untouched for years.

Looking at the issues list more closely, there seem to be two open issues involving capture decode quality: one unanswered one from earlier this year, and one from more than two years ago that was responded to but not resolved. I'll try to open another issue, but I'm not optimistic about having it resolved.

User avatar
mikeysklar
 
Posts: 13936
Joined: Mon Aug 01, 2016 8:10 pm

Re: I2CMini/Driver poor decode quality?

Post by mikeysklar »

Opening an issue with them at least documents the decode quality concern and other users might also have suggestions (custom firmware build?).

Also please try the [email protected] email.

Locked
Please be positive and constructive with your questions and comments.

Return to “Other Products from Adafruit”