Date   : Mon, 05 Jan 2015 20:55:33 +0000
From   : public@... (Daniel Beardsmore)
Subject: Serial console active at power-on

On 2015-01-05 19:40, nicola giacobbe wrote:
> About the keyboard suggestion (i.e. to remove it) and the technical
> insight that followed, my original idea was to have an FPGA to
> simulate the keyboard ...

You might be thinking of a PC keyboard, which typically has a single chip
that handles everything from strobe and sense through to the communication
protocol. I think some really old keyboards would actually output pure ASCII
codes instead of scancodes.

The BBC Micro keyboard isn't like that: strobe and sense comprises around 
four small chips and that's all you've got on the keyboard PCB (and interestingly, 
being such lowly chips, they're not endowed with manufacturing date codes
like some larger chips are including full-on keyboard controllers from the
likes of Intel, Daewoo/Appian and Signetics).

I assume that the keyboard controller code is actually inside MOS itself, 
which uses the system VIA to communicate with the chips on the keyboard PCB.
You'd have to actually simulate the low-level circuitry on the keyboard PCB,
and I imagine that's going to be even more of an adventure than writing a
sideways ROM!

> Thanks a lot John, this is a good suggestion which, combined with
> the previous e-mail will let me complete the project easily. Thanks
> to all in the mailing list, I did not imagined that removing the 
> keyboard could spur so many troubles.

>From my limited experience, one failure mode I know all too well is the 
MODE 0 hang when the keyboard isn't properly connected! I always thought
that this was due to POST failing, not that the OS had finished starting
and was waiting for the user to release ctrl+shift.