Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site utcsri.UUCP
Path: utzoo!utcsri!greg
From: greg@utcsri.UUCP (Gregory Smith)
Newsgroups: net.micro.apple
Subject: Re: Apple //e Interrupts
Message-ID: <3222@utcsri.UUCP>
Date: Mon, 4-Aug-86 01:06:22 EDT
Article-I.D.: utcsri.3222
Posted: Mon Aug  4 01:06:22 1986
Date-Received: Wed, 6-Aug-86 10:20:49 EDT
References: <283@ski.UUCP>
Reply-To: greg@utcsri.UUCP (Gregory Smith)
Organization: CSRI, University of Toronto
Lines: 82
Summary: 

In article <943@rti-sel.UUCP> jb@rti-sel.UUCP (Jeff Bartlett) writes:
>> >I haven't seen mention of this, but interrupts during disk I/O
>> >can corrupt your disk.
>> >
>> >I have to agree that the Apple ][ family is really not designed
>> >for real-time, multitasking use.  There's no reason it shouldn't
>> >have been, except they didn't think of it in the first place.
> 
>> Oh yeah? Any idea how much cost was saved ( way back when ) by making the
>> CPU work its tail off in disk I/O, rather than using an LSI disk controller
>> chip ? ( Not to mention trimming everything from the drive, e.g door switch,
>> index hole sensor, track zero sensor. TUKATUKATUKATUKATUKATUKA!!)
>> 
>> Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg
>
>An Apple ][ with software disk control will beat a
>   Radio Shack model II (w/controller) hands down in disk performance.

My brother recently purchased a //c ( which is why I am reading this grp ) and
I am impressed at the speed of the disk. But I imagine your comparison is
more of a reflection on the Radio Shack...

I have an EPSON QX-10 ( "A WHAT??" I hear you say...) with controller and DMA.
With one of the operating systems, a BIOS call to write the disk will return
immediately and perform the write in the background, even if the drive needs
spinning up first. 
The point is that the Apple implementation makes it impossible to handle
interrupts ( or anything else ) during disk i/o.

>
>   * Faster track to track seek time.
>   * Higher density.
>   * Fast transfer times.

Yes, and the latter two are impressive, given the software support required.
>
>Also you can operate the disk spinning backward, or lay down spiral sectors.

Can you operate the disk spinning backwards? Do Tell.
As for spiral sectors, the inability of hardware to do such nasties protects
users from horrible copy-protection schemes. This applies to half-tracking,
as well.

>
>Maybe they should include a 2nd CPU on-board to process IO.
>
>(My grip is:
>    "why didn't they tie the parallel keyboard input into the interupts",
>'Can you say "POLL" boys and girls?, I thought you could.' )

Yes. Can you say "No typeahead without the software doing handstands?"
Even a keyboard interrupt would not allow typeahead during disk i/o
without a 'real' disk controller.

The problem with all this, is that any mods to the Apple II line must
be compatible with all previous software. 90% of the value of an Apple
is due to this software base.  If this were not the case, the //e would have
been VERY different. They would have used a CRT controller chip to
straighten out the screen addressing, e.g., and they might even have
switched to a decent processer.

Don't get me wrong, the original design of the Apple ][ gave excellent
performance for the price at the time ( sure beat the PET ). But the
momentum of compatibility has caused much grief as the machine has
outlived its design. Of course 96% of users will never know
or care about this, but dyed-in-the-wool bit-hackers like me will...

What bothers me is that even the Apple //c goes 'TUKATUKATUKATUKA' when
aligning its head. If the processor sent 'step in' and 'step out'
pulses to the hardware, it would be a simple matter to add a track-0
sensor and disable the step-out signal when it sensed track-0. It seems (?)
that the CPU directly controls the stepper-motor coil signals though, so
this annoying noise cannot be easily eliminated without modifying the CPU's
view of the controller, which would break software that bypasses DOS and
would thus be Impossible. I believe Apple would have loved to eliminate
this if it were possible to do it at reasonable cost. 

-- 
"You'll need more than a Tylenol if you don't tell me where my father is!"
						- The Ice Pirates
----------------------------------------------------------------------
Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg