Re: Olimex Lime 2 Board

[Denis 'GNUtoo' Carikli]

On Fri, 13 Sep 2024 02:52:33 +0000
myrcy@posteo.net wrote:

> Hello everyone,
Hi,

> Can users utilize the Olimex Lime 2 Board to flash their hardware? I 
> would love to help be a guinea pig and help test it out.
I think it should be possible but as far as I know no one documented
it (we need help for that).

Here's an example of how to do if you want to try:

- Unless you're very good at soldering and confortable with soldering
  on tiny pins, you will also need a cable and an adapter[1] to be able
  to have regular (2.54") pins headers.

- Then the next step is to understand to what pins you need to connect
  your clip. Olimex probably has documentation on that, so it shound't
  be that hard to find out.

- Then the next step would be to try it and see if it works. It might
  not work because the pins usually have multiple functions (like GPIO
  or SPI) and you might need to reconfigure that.

  If you need to reconfigure the pins, the easiest way to make it work
  for everybody do it would be to send a patch to Parabola (to the
  linux-libre kernels) to provide a patched devicetree and document
  how to use that somehow, or to provide patched devicetree in another
  Parabola package and also document how to use it.

  At home I use custom hardware, and so I also needed to patch the
  devicetree to reconfigure some pins to be GPIOs or buttons on a
  beaglebone black/green[2], so it could be used as an example on how
  to do it, however I didn't spend time integrating it in Parabola
  because I'm the only person with that use. Also there is a small
  issue in my code: it doesn't use exactly the same devicetree than the
  one Parabola ships as a base, and so it might not contain bugfixes
  and so on, but it's usually good enough for my use case. The
  advantage is also that it's much faster and much easier to do tests
  with that (you don't need to recompile a complete kernel).

  In your case however it makes sense to also work with Parabola to
  upstream your work since it is potentially useful for a lot more
  people. I didn't do that because it's custom hardware and I'm the
  only user.

Also, you will also need some way to measure the voltage as we don't
know how much current the Lime2 can provide. The issue is that when you
connect the lime2 to the flash chip, it will power it and it might also
power what's around it as well. So if it doesn't provide enough current on
the pins you use, the voltage will drop.

If it doesn't provide enough current you might need to provide 3.3v
from another source into the flash chip between the VCC and GROUND pins
of that chip, and also ask around if this doesn't put at risk the lime2
somehow (I don't think it could, but it's still a good idea to ask
somewhere where they could have an answer like you could try to ask
olimex and/or the community using lime2 and/or #electronics on IRC,
etc).

In general it's also a good idea to read the documentation about the
pins as sometimes there is some safety information with them. For
instance for the beaglebone green, there are some pins that don't
tolerate 5v and you risk frying the CPU if you do that, while other can
tolerate more abuse and/or higher voltage ranges.

And if you try what is in this mail, it would make things easier if
you document what you do along the way as it could help writing the
missing documentation.

Also note that I've a lime2 but I don't have the UEXT adapter and I
also need to reinstall it, so I can't really help with testing, but I
can still review patches nevertheless.

References:
-----------
[1]https://www.olimex.com/Products/OLinuXino/A20/A20-OLinuXino-LIME2-UEXT/open-source-hardware
[2]https://git.sr.ht/~gnutoo/bmc/tree

Denis.

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