Date   : Sun, 29 Jul 2007 10:34:27 +0100
From   : adsb@... (Andrew Benham)
Subject: Comms software

gARetH baBB wrote:

> Hardware flow control is not really the problem, the OS buffering system 
> and IRQ setup is just too slow to cope with 19200 bytes/s.

I think the missing text here is 'sustained use at'.  The BBC can't
send 19200b/s at a rate that saturates the serial link (i.e. there
are inter-character gaps), and it can't keep up with receiving a
saturated 19200 link.

As I recall, there was a cryptic note to this effect in the documentation.

The BBC has only one IRQ line, and has to poll all possible interrupt
sources to determine which device needs servicing.  This takes extra
time.  I seem to remember that the UART is checked twice, once at the
top of the interrupt routine and again at the bottom, to improve
performance, but it still isn't quite enough for sustained 19200.

-- 
Andrew Benham         adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill"