I2C: garbage output on DragonBoard410c

[ric96]

I get garbage OR whatever was there on the last frame displayed on the display, and the code hangs for a long time.
Here is an example of the oled displaying the last frame, while running the demo code in readme:

This library is working as expected, so at least its not hw.
https://github.com/codelectron/ssd1306

[ladyada]

do you know for sure that display is SSD1306? knockoffs often use other chipsets

[deshipu]

In particular, SH1106 is very popular, but sadly it doesn't support the addressing mode that SSD1306 uses by default (so most drivers won't work).

[ric96]

I've tried this display with Arduino, Zephyr, MRAA and the above mentioned library all worked fine so i'm assuming its SSD1306.

[makermelissa]

What is the exact code that you're running and what are the dimensions of that display? I'd like to test it out on a similar setup with an equivalent Adafruit display.

[makermelissa]

A couple of things I just thought of are if this is running on the DragonBoard 410c and you're using a logic level shifter:

1. Make sure it's I2C Safe such as https://www.adafruit.com/product/757
2. Make sure VCC is 3.3v and not 5V or at least the same voltage as the logic levels.

[ric96]

@makermelissa running the code that is in the Readme of this repo under usage example.
I've got a bmp280 working fine with this very setup.
I've separately tried a 128x32 and 128x64 oled display. Both of these had the i2c address set to 0x3c if that helps.
Again, the display works fine using another library so i think I'm good on the level shifter end.
PS. Using the Audio Mezzanine as the level shifter. This has worked well for i2c usecases over the years.

[makermelissa]

Hi, I finally got around to testing with https://www.adafruit.com/product/931 on the DragonBoard and can confirm that the issue occurs (random dots plus hanging) with Adafruit displays as well.

[makermelissa]

After hitting Control-C and waiting a couple minutes, I finally got this error output in addition to the expected keyboard interrupt error:

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/adafruit_bus_device/i2c_device.py", line 68, in __init__
    i2c.writeto(device_address, b'')
  File "/usr/local/lib/python3.7/dist-packages/busio.py", line 65, in writeto
    return self._i2c.writeto(address, buffer, stop=stop)
  File "/usr/local/lib/python3.7/dist-packages/adafruit_blinka/microcontroller/generic_linux/i2c.py", line 38, in writeto
    self._i2c_bus.write_bytes(address, buffer[start:end])
  File "/usr/local/lib/python3.7/dist-packages/Adafruit_PureIO/smbus.py", line 244, in write_bytes
    self._device.write(buf)
OSError: [Errno 22] Invalid argument

[makermelissa]

I wonder if this is related to adafruit/Adafruit_Python_PureIO#4

[ladyada]

probably not, smbus is the native I2C library/interface, havint it in pureio would be rad, but its really not essential. also repeated start isnt used on this display

[makermelissa]

Ok, good to know :)

[ric96]

Hi,
any updates on this?

[makermelissa]

Hi, thanks for checking in. I was planning on taking another look at this later this week.

[makermelissa]

I think I may have found something in that Blinka has trouble with i2c write-only devices on certain boards (DragonBoard 410c and Jetson Nano I've found). I'm looking into this further.

[makermelissa]

This might just need a reset line hooked up. I've seen similar behavior with microcontrollers. That solution will probably only work with the displays that have a reset line though.