Hyperpixel i2c [Errno 121] Remote I/O error

Support
1

Hi,

I am trying to get the Hyperpixel i2c interface to work. I have a brand new Raspberry Pi 4, running 64bit raspbian. I have been following the guide here https://learn.pimoroni.com/article/getting-started-with-hyperpixel-4.

I get the display to work. I get touch to work. However, I am unable to run the command:
sudo ln -s /dev/i2c-3 /dev/i2c-1

I get the error:

ln: failed to create symbolic link '/dev/i2c-1': File exists

ls /dev | grep i2c gives me:

i2c-1
i2c-20
i2c-21
i2c-22

I can run i2cdetect -l, which gives me:

i2c-20	i2c       	Broadcom STB :                  	I2C adapter
i2c-1	i2c       	bcm2835 (i2c@7e804000)          	I2C adapter
i2c-21	i2c       	Broadcom STB :                  	I2C adapter
i2c-22	i2c       	i2c@0                           	I2C adapter

If I run my script using example code from here, I get the following error:

File "/myscript.py", line 81, in main
    ioe = io.IOE(i2c_addr=0x18)
  File "/usr/local/lib/python3.9/dist-packages/ioexpander/__init__.py", line 345, in __init__
    chip_id = (self.i2c_read8(REG_CHIP_ID_H) << 8) | self.i2c_read8(REG_CHIP_ID_L)
  File "/usr/local/lib/python3.9/dist-packages/ioexpander/__init__.py", line 353, in i2c_read8
    self._i2c_dev.i2c_rdwr(msg_w, msg_r)
  File "/usr/local/lib/python3.9/dist-packages/smbus2/smbus2.py", line 658, in i2c_rdwr
    ioctl(self.fd, I2C_RDWR, ioctl_data)
OSError: [Errno 121] Remote I/O error

My /boot/config.txt has these (I believe) relevant lines:

dtparam=i2c_arm=on
(...)
dtoverlay=vc4-kms-dpi-hyperpixel4
dtparam=rotate=270,touchscreen-swapped-x-y,touchscreen-inverted-x

For further debugging, this is what i2cdetect -y X gives me:
i2cdetect -y 1

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

i2cdetect -y 20 and i2cdetect -y 21 (their outputs are identical):

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         08 09 0a 0b 0c 0d 0e 0f
10: 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
20: 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f
30: -- -- -- -- -- -- -- -- 38 39 3a 3b 3c 3d 3e 3f
40: 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f
70: 70 71 72 73 74 75 76 77

i2cdetect -y 22

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- UU -- -- -- 18 -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

I have never worked with i2c before, and must admit I am fumbling a bit, not really understanding the i2cdetect command. Any help would be greatly appreciated!

2

all the files in /dev are hardware-related. You cannot just create a symbolic link from /dev/i2c-1 to /dev/i2c-3. Well you could if /dev/i2c-1 did not already exist, but it exists as you can see from your i2cdetect command: it is the i2c-bus on the bcm2835.

But even if /dev/i2c-1 did not exist already, you would not do something like that.

3

You cannot just create a symbolic link from /dev/i2c-1 to /dev/i2c-3

Thanks. I assumed that was the case, but I was following the getting started guide. Strange that the guide shouldn’t work as I’m working on a brand new Raspberry, and a brand new Hyperpixel.

Still struggeling with this one…

4

I can see it in the getting started guide but I’m scratching my head.

The question is: what is missing? Do you need I2C for external devices? And the strange thing is: the installation routine should create an I2C-3 device (on GPIO10/11), which it obviously does not.

One thing to try: connect an I2C-device to the connector on the back. Then run your i2cdetect commands to see on which bus it is.