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Re: [MirageOS-devel] Writing to Multiple Serial Ports

Hi Paul, Aaron,

On Tue, Oct 6, 2015 at 8:27 PM, Paul Skentzos <paul.skentzos@xxxxxxxxxxxxxxx> wrote:
We are trying to access a serial port passed to a domu. We're very new to Mirage
and ocaml, but plan on converting our existing system to use MirageOS for
various domU's.

So, at the moment, the question we have is whether anyone has had any success
writing to multiple serial ports with one of those serial ports being accessed
from a domu?

As a first attempt, we took the Mirage console example and added a second
console. We connected it to '1' and then to /dev/null and tried to print to it.
Neither of the ideas were valid. We're not sure what the console should be named
or what the hashtbl is looking for. The application compiles, but the VM halts
with a message stating. "... waiting for hotplug". The application built for
unix didn't work either.

We are trying to read data from a GPS receiver from a domu.

Interesting! Is the GPS receiver connected to a physical serial port on the host?

The virtual serial ports that Mirage can see need to be served by something on the host (a "backend", typically in dom0). If you're creating your VM with "xl create" then you can declare "channels"[1] which will spawn a qemu process in dom0 which will act as the server/backend. At the moment the backend can only be connected to a fresh tty or a Unix domain socket -- there is no built-in support for proxying to a real /dev/ttyS* device.

I think the first thing to do is to verify that adding a 'channel' to your xl config file causes the Xen domU to get further than "waiting for hotplug". After that I think you could declare the backend to be a Unix domain socket, and then run a proxy in dom0 which would write the data to the appropriate ttyS device.

Sorry that's a bit clunky -- when I added the channel support to "xl" I didn't think about the possibility of a real serial port. I'm sure that could be added in future though.

What do you think?

Dave Scott

Any ideas where we should look for getting this capability?

I appreciate the help!

Paul Skentzos
Aaron Cornelius

MirageOS-devel mailing list

Dave Scott
MirageOS-devel mailing list



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