RP2: Hard I2C not working

[massimosala]

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Port, board and/or hardware

rp2

MicroPython version

MicroPython v1.22.2

Reproduction

from machine import Pin, I2C
from ssd1306 import SSD1306_I2C
bus = I2C(id = 0, scl = Pin(9), sda = Pin(8), freq = 100_000)
display = SSD1306_I2C(128, 64, bus)

Expected behaviour

ssd1306 working

Observed behaviour

Failure with errors EIO / ETIMEDOUT.

Tested with id 0 and 1, on different pins.
Works like a charm using SoftI2C.

Additional Information

Could be related to this ticket ?
RP2: Hard I2C is intolerant of clock stretching
#8167

[peterhinch]

I have used the following with two different designs of I2C hardware:

i2c = I2C(1, scl=Pin(27), sda=Pin(26), freq=100_000)

You might want to try that setup and pins and run I2C.scan().

[massimosala]

Hi Peter.

As per your request, I make a new test.
Setup: official Raspberry rp2 and generic ssd1306 display. No other components.

I used these displays from over a year, they have fixed i2c addr 0x3c.
They consume very little, so I wired their Vdd to rp2 pin 36 (3.3 Vout).

Testing I2C:
bus = I2C(1, sda = Pin(26), scl = Pin(27), freq = 100_000)

It fails:

Traceback (most recent call last):
File "", line 1, in
File "web_display_ex.py", line 302, in
File "ssd1306.py", line 1, in init
File "ssd1306.py", line 1, in init
File "ssd1306.py", line 1, in init_display
File "ssd1306.py", line 1, in show
File "ssd1306.py", line 1, in write_data
OSError: [Errno 110] ETIMEDOUT

Testing Soft i2c:
bus = SoftI2C(sda = Pin(26), scl = Pin(27), freq = 100_000)

No errors, the display works.

@peterhinch, are you trying with the same configuration: rp2 with ssd1306 display?

Perhaps the ssd1306 is a bit finicky... but on esp8266 and esp32 the I2C works fine with these displays.

[Flipje1955]

use various brands rp2's with ssd1306 and have no issues using "hard" fast i2c but have 4k7 pullups on the i2c pins. U2 ?

[massimosala]

Hi @Flipje1955

use various brands rp2's with ssd1306 and have no issues using "hard" fast i2c but have 4k7 pullups on the i2c pins. U2 ?

Certainly I have pullups, otherwise SoftI2C doesn't work too.
I use 5.1k resistors.

[robert-hh]

About scan and RP2: scan() just sends the address. In that case there is no data and SoftI2C is used, even when the Hard I2C API is called.