Re: Beginner question about GPIO and mirage build process

[Nick Betteridge <lists.nick.betteridge@xxxxxxxxx>]

Hi Michael,

Please forgive this delayed response - I've been trying to think of an 
elegant and easy way of setting up a path between a gpio and unikernels.
There are no interfaces per-se dealing with direct io interaction. 
However, you could try writing a device interface for the backend using 
the block [1] or kv [2] signatures - the '-unix' give the unix 
implementations.
There are gpio bindings [3][4] which you could look at and there's also 
a good example of reading/wring to a gpio/memory in rpi-boot-ocaml [5]
Hope this helps and happy hacking!

Nick

[1] https://github.com/mirage/mirage-block/blob/master/src/mirage_block.mli
[2] https://github.com/mirage/mirage-kv/blob/master/src/mirage_kv.mli
[3] https://github.com/vbmithr/ocaml-gpio
[4] https://github.com/LaurentMazare/ocaml-rpi-gpio
[5] https://github.com/dbuenzli/rpi-boot-ocaml/blob/master/src/rpi.mli

On 19/02/2021 21:56, Michael Chiu wrote:
> Hi Everyone,
>
> I was hoping to get some help / advice on two related issues.
>
> 1. I'm new to both OCaml and MirageOS and am trying to figure out how to 
> access GPIO when targeting a unix backend. I've looked at all the 
> tutorials and have a basic understanding of how mirage works, but 
> couldn't find more in depth documentation on what's happening behind the 
> scenes, or what the available configuration options are for. Does the 
> unix backend have support for GPIO? Is there some documentation that I 
> haven't found?  I'd appreciate some advice to better understanding 
> mirageOS.
> 2. I'm not too familiar with the build system in both ocaml and 
> mirageos, but I do know how to make a simple module package using dune. 
> I'm trying to get a custom module working in mirage but it's unclear to 
> tell the mirage toolchain about my custom module.
> Any suggestions are appreciated, thanks in advance.