Date   : Fri, 28 Aug 2009 00:00:55 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Tube FIFO

Jason Flynn G7OCD wrote:
> Upon reading the Acorn application note 004 (Tube) I note
> that at one point it says the large FIFO will be at least 10
> words deep and then the schematic shows 24.
> 
> Can anyone give any information on:
> 1) What size the large FIFO in a real Tube device actually is.
> 2) Whether a different FIFO size (say 8,16 or 32 words deep)
> would have any major impact on performance/compatibility.
 
At least 10 items in the VDU FIFO allows a whole 10-byte VDU 23
sequence to be sent with no pause. A larger FIFO will will let the
client send more VDU characters before having to wait for the I/O
processor to deal with them, but the impact drops off as the client
will be spending more time processing than waiting to send a VDU
character.
 
If designing a Tube ULA replacement, you can get away with one-byte
FIFOs, as each side polls for empty/full, and a deep FIFI O just
lets more data be pushed into the ULA before you have to wait for
it to be taken out of the other side.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC BASIC for Windows and Internationalisation
  See http://mdfs.net/Software/BBCBasic/Windows/ProgTips