Re: COM port usage in UEFI

[Michael Zimmermann <sigmaepsilon92@gmail.com>]

COM ports may have had a naming scheme in past but in recent windows
versions you are allowed to assign any COM name to any device - even USB.

So he should really just obtain a handle to the correct protocol and try to
choose/configure the correct port if there is more than one.

Thanks
Michael

On Tue, Oct 25, 2016 at 6:50 PM, Andrew Fish <afish@apple.com> wrote:

>
> > On Oct 25, 2016, at 2:30 AM, GN Keshava <keshava.gn@gmail.com> wrote:
> >
> > Hi all,
> >
> > In my UEFI application, I'm using Serial protocol to access COM port. I'm
> > able to access COM port successfully.
> >
> > But I'm confused on how we can get user input regarding which COM port
> the
> > user wants to access.
> >
> > *Example, I have already a Windows application for the same, where user
> > selects the COM port number he wants to access, such as COM1: , COM30:
> etc.*
> >
> > In UEFI, I'm using COM port Handle Index (which user gets/uses in
> > *sermod *command,
> > like , *myapp.efi 31F* , where 31F is com port handle index).
> >
> > Is this best way possible in UEFI? Or is it better to use HANDLE itself?
> Or
> > is there any way to get input as COM port number same as Windows app?
> >
>
> Keshava,
>
> COM ports are kind of an early PC and DOS concept. I think the naming
> convention for COM1 - COM4 is based on I/O port and after that I'm not
> clear how it works, I guess that is made up by the OS?
>
> The ISA base (PC) Serial Driver is here: https://github.com/tianocore/
> edk2/tree/master/IntelFrameworkModulePkg/Bus/Isa/IsaSerialDxe <
> https://github.com/tianocore/edk2/tree/master/IntelFrameworkModulePkg/Bus/
> Isa/IsaSerialDxe>
>
> Looks like it produces a Component Name protocol that produces human
> readable strings for the port. That is probably the best thing to use in
> EFI. The other alternative is to use the device path on the handle, and
> attempt to decode that, but in doing that you are making assumptions about
> how the hardware works, so that could fail. For an ISA Bus there should be
> an ACPI Device Path node that has the HID and UID for the device.
>
> Thanks,
>
> Andrew Fish
>
> > Thanks!
> > Regards,
> > Keshava
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