Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!mit-eddie!killer!elg
From: elg@killer.DALLAS.TX.US (Eric Green)
Newsgroups: comp.sys.cbm
Subject: Re: Simultaneous disk & RS-232 access
Message-ID: <7023@killer.DALLAS.TX.US>
Date: 3 Feb 89 06:34:17 GMT
References: <738@csd4.milw.wisc.edu>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 62

in article <738@csd4.milw.wisc.edu>, jgreco@csd4.milw.wisc.edu (Joe Greco) says:
> In comp.sys.cbm article <89Feb1.163849est.2383@godzilla.eecg.toronto.edu>, leblanc@eecg.toronto.edu (Marcel LeBlanc) wrote:
> ]about 10 mins.  Thats 173K/10mins, or about 290 bytes/sec.  If we assume
> I don't know where you pull these figures from.... my clocking of
> serial has always been somewhat higher (perhaps 500cps).  However,
> that does not account for the 1541's slow write time....

I informally clocked it at around 360-380cps, doing a "load" using
normal Kernel routines (which is just calling the normal serial
get-a-char routine). 

As for the 1541's slow write time, I have NOT clocked that recently,
but would assume it's slower than the read times, especially
considering its design.

> ]obvious solution:  read from/save to a RAM buffer, and use fast disk I/O

This is, certainly, an obvious solution (you might remember, Marcel,
that I suggested this as a way of speeding up sequential file access).
It needn't be a large RAM buffer. Even buffering just 1 block at a
time would be worthwhile. Just compare C-128 Burst Mode speeds with
C-128 Fast Mode speeds.... Burst Mode transfers the bytes at the same
rate, but blows off per-byte negotiations (uses per-block
negotiation), and is considerably faster (4 or 5 times so on reads,
much less so on writes because of the design of the 1541/1571).

Another solution to the disk drive speed problem would be to use a 128
with a 1581 ;-). If you're really wanting to use your 64 to do it,
there should be products out there that add fast serial to your 64.
Note: "burst mode" is NOT a software product. People who say they give
you "burst mode" with a software cartridge that plugs into your
computer are LYING. Burst mode requires hardware, whether via hacking
the insides of your 64, or adding an external CIA (fast mode & burst
mode use the internal shift register of a CIA to shift data in and
out under hardware control, at 256kbps or 1 bit per every 4 clock
cycles). I don't know whether advertisers are simply ignorant, or are
trying to decieve, but that's something to think about.
     Of course, hardware burst mode isn't cheap... I once estimated
that it would cost at least $100 for a company to make money off the
easiest-to-install setup (external CIA, buffers, & bank-switching ROM,
with only two jumpers into the internals of your computer).

> 
> The only thing I don't like is device specific programming.  I use CBM
> 8050 drives nearly exclusively, with a BusCard II, and nasty tricks
> like fast disk I/O won't work.  Somebody who wrote Z-Modem using a
> fast disk I/O would earn my eternal hate... hehehe
> 
> You might also run into some flames from the 1581 folks.

He won't run into flames from the 1581 folks, because his product
already supports the '81 ;-). I just wish that "burst mode" wouldn't
be used in conjunction with such software speedups... because true
burstmode is at least twice as fast as anything you can do with
software (256kbps, 25 kbytes/second, but that's slowed slightly
because you do have to toggle the clock after each byte transfer,
fetch the byte out of memory, etc.). 

--
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