Newsgroups: comp.sys.cbm
Path: utzoo!utgpu!jarvis.csri.toronto.edu!godzilla.ele.toronto.edu!leblanc
From: leblanc@godzilla.ele.toronto.edu (Marcel LeBlanc)
Subject: Re: Burst Mode on C-64 ?
Message-ID: <8806010545.AA22977@godzilla.ele.toronto.edu>
Summary: High bit rates through software
Organization: EECG, University of Toronto
References: <1988May27.175829.5648@ziebmef.uucp> <4241@killer.UUCP>
Date:	Wed, 1 Jun 88 00:25:16 EDT

In article <4241@killer.UUCP> elg@killer.UUCP (Eric Green) writes:
>in article <1988May27.175829.5648@ziebmef.uucp>, ross@ziebmef.uucp (Ross Ridge) says:
>> On a local BBS we had a discussion about burst mode on the 64. We thought the
>> biggest problem would be be the hardware modifications, but our goal was to
>> be able to do it through software only. The CIA's (6526) serial port *could*
>> be emulated through software (side note: the 64 can go as high ar 4800 baud
>> or 7200 half-duplex if you completely re-write the RS232 routines) however
>> burst mode used serial line that wasn't connected on the 64...
>
>Note that bit-rate for each byte during burst mode is 250,000 baud, not 4800
>baud. Burst mode is FAST. With the 1581, which reads data off disk at a
>reasonable rate, the 128 is almost as useful as a real computer.
	8-)   It IS a real computer !   8-)	   ^^^^^^^^^^^^^
>You'll never do it in software. In particular, the 1581, in fast mode or burst
>mode, clocks data out at 250,000 baud. No software in the world is going to be
>able to sample fast enough to cope with that. Hardware is necessary. Period.

	I agree that software can't compete with hardware for raw speed, but
it is indeed possible to transfer data at very high rates over the commodore
serial bus (even at BURST speeds!).  The first thing thing that must be
pointed out is that the 250,000 bps BURST transfer rate is nowhere near the
effective file transfer rate using present commodore burst software.  Using
the commodore burst protocol, the CLK bit must be toggled (by software)
after each byte transfer.  During this time, the bus is idle.  The result is
a very short period of very high speed transmission (for a single byte),
followed by a relatively longer idle period where only the CLK bit is
toggled.  Also consider that although the 1581 is very fast because it makes
use of a disk cache, some time is required to read each half track into the
cache, then transfer sectors from the cache to the file buffers before each
sector is transmitted to the C128 (assuming LOAD operation).  It turns out
that the effective transfer rate for LOAD operations using a 1581 is only
about 50,000 bps, or 6Kbytes/sec (still much higher than 4800 baud).
	The point of this posting is to point out that the SAME speed or
faster can be achieved on a vanilla C64 using only special software.  The
1581 turbo LOAD routines on Super Snapshot V3.0 (using a C64) are the same
speed as BURST loading with a C128 & 1581 (turbo SAVE is faster with SS V3.0
than with C128 BURST save).  In more concrete terms, this means that you can
load a 202 block file on a C128 or C64+SS(V3.0) from a 1581 in 9 seconds.

...
>If you are doing true burst mode, and not just a software fastload/fastsave
>routine. 

	The C128 kernal only supports BURST mode for loads and saves.  For
other types of transfers, either fast serial or slow serial transfers are
supported (in the case of the 1581, this will always be fast serial).  I
don't find that fast serial is a significant speed improvement over slow
serial.  It doesn't even come close to the speed of BURST transfers.
Although other specialized types of BURST transfers are supported, these
require custom software.

>    Eric Lee Green                     {cuae2,ihnp4}!killer!elg

  Marcel A. LeBlanc
  University of Toronto -- Toronto, Canada
  also: LMS Technologies Ltd, Fredericton, NB, Canada

CSNET:	leblanc@godzilla.ele.toronto.edu   CDNNET: <...>.toronto.cdn
UUCP:	{decvax,ihnp4,linus,utzoo,uw-beaver}!utcsri!godzilla.ele!leblanc
ARPA:	leblanc%godzilla.ele.toronto.edu@relay.cs.net
BITNET:	leblanc@godzilla.ele.utoronto (may not work from all sites)