Date   : Sun, 29 Jul 2007 16:40:40 +0100
From   : info@... (Sprow)
Subject: Comms software

In article <46AC6AF2.2060009@...>,
   Andrew Benham <adsb@...> wrote:
> Sprow wrote:

> > Isn't that why you can set the handshake threshold with OSByte 203?
> > Presumably a reliable link can be achieved by increasing this value from 
> > its default of 9 to (say) 18 or higher?
>
> Sorry, that's too late.  The bottleneck is in the interrupt service
> routine, reading the characters from the UART and putting them in
> the buffer.  

Another plan foiled.

> I'm now thinking whether there's a way to put a 16550 on the 1 MHz bus
> and use NMI to handle it.  Could speed up my program to backup my hard
> disk to the serial port...

Could you just lift the IRQ pin out of its socket and wire it across to
somewhere near S9? The MOS wouldn't see UART IRQs any more and you'd be free
to write an NMI handler to get bytes yourself, or one of my second serial
port boards
  http://www.sprow.co.uk/bbc/extraserial.htm
with a track cut from IRQ and wired to NMI,
Sprow.