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I was wondering whether or not e.g. GPIO 1 should be used for connecting to EEPROM's only, or whether it is still fully functional for all other purposes.

It could maybe also be that the pin is only used for EEPROM's because of convention, I am not sure.

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Q: "Is GPIO 1 functional for other purposes?"

Yes, it is. Most GPIO pins on the RPi are functional for other purposes. You can see this in the 3rd party pinout guide, for example.

Perusing the README file (/boot/overlays/README on your local filesystem, or in the GitHub repo) may give you additional insights into other uses for GPIO 1 available via overlays in the device tree. For example, on the RPi 4, GPIO 1 may be designated as the SCL for the i2c6 bus by using the dtoverlay=i2c6 overlay.

You may also choose to use GPIO 1 simply as digital input or output; GPIO = General Purpose Input Output.

In general however, it is likely safer to use GPIO pins in accordance with their default configuration unless there are reasons to deviate from that.

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  • Have you ACTUALLY tried this?
    – Milliways
    Oct 3, 2021 at 20:55
  • @Milliways: Which usage do you feel is incorrect?
    – Seamus
    Oct 4, 2021 at 4:37
  • I didn't say it was incorrect, I asked "Have you ACTUALLY tried this?" While I have used GPIO0 on a B+ using Wheezy it didn't seem to work last time I tried on a modern Pi/OS which AFAIK use the reserved I²C for internal purposes.
    – Milliways
    Oct 4, 2021 at 5:35
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To answer the Question you actually asked "Does GPIO 1 have to connect to an EEPROM?"

No - I don't use HATs so there is nothing connected.

It is possible to "prevent the firmware from trying to read an I2C HAT EEPROM (connected to pins ID_SD & ID_SC) at powerup" using force_eeprom_read=0.

See https://www.raspberrypi.org/documentation/computers/config_txt.html#force_eeprom_read

This does not necessarily mean you can use the pins for other purposes (which is undocumented).

My attempt to set GPIO0 as output shows ERROR: no permission to update GPIO

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