[arch-general] Access for ordinary users to USB FTDI devices

Friedrich Romstedt friedrichromstedt at gmail.com
Sat Jun 27 12:29:32 UTC 2020


Since end of 2019 I am using the PyFtdi Python package by Emmanuel
Blot to talk to an FTDI chip on some controller board. Documentation
of PyFtdi is hosted on http://eblot.github.io/pyftdi/. FTDI (Future
Technology Devices International) chips (and similar chips by other
vendors) implement an Universal Asynchronous Receiver Transmitter
(UART) via USB. This can then be used to send messages to the device
and receive replies. According to
http://eblot.github.io/pyftdi/installation.html, it is at least on
Debian and Ubuntu Linux necessary to write an `udev` rules file in
order to permit ordinary users access to such an USB device. I
attempted to use PyFtdi on my Arch Linux box (patched daily) as an
ordinary user, and successfully talked to the device without any
additional `udev` rule. We (Emmanual and me) would like to find out
why and how Arch is configured to permit this. As I observed this
behaviour, I opened Issue #161 on https://github.com/eblot/pyftdi:
https://github.com/eblot/pyftdi/issues/161. There were some posts by
Emmanuel and by me, but we didn't achieve anything substantial so far.
Furthermore, the question arises if there are more places other than
PyFtdi where this result might be relevant. Finally it might apply
also to other Linux distributions different from Arch Linux aside
Debian and Ubuntu; the documentation of pyftdi maybe could be updated
to reflect this.

Any pointer is welcome.
Best wishes,

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