Re: Handic VIC-Switch

Den Thu, 2 Nov 2017 10:31:52 -0400 (EDT) skrev Jim Brain
<brain@jbrain.com>:
> C128 #1 gets a bit ahead of the rest, and so the switch immediately
> connects #1 to the bus

It was me who started this thread. I would actually prefer if the boot
procedure of a C128 fails if I don't push some button on the switch or
similar. (Maybe I forgot some key combination that skips the auto boot
of the C128, except C= key for C64 mode)? Making auto boot fail could
be implemented by a delay from a reset pulse until letting a
computer on that port access the bus.

> Once the bus calms down, the cycle will repeat.  For any situation
> where a second computer accesses the bus while another computer
> already "owns" the bus, burst mode will not be available for the
> subsequent devices, until the bus calms down again.  That sounds like
> an annoyance but not a real problem, however, if a 128 sends a few
> burst commands successfully, will it be able to send the next command
> to the same device, not get burst mode, and be OK?  Or, is there a
> flag in the 128 that is set during OPEN that indicates the device is
> burst capable.  And, the rest of the communication assumes (a
> reasonably valid assumption) that the device continues to be burst
> capable.  If so, then your idea will cause hangs if there is any bus
> contention.

This is something worth investigation :)

Also I thing you are correct in that doing slow transfers with
open/input#/print#/get#/close will fail if they use the same channel /
secondary device.

I can live with that. I would probably not do much database management
on my VIC-20 :)

Probably the most common use case where more than one controller wants
to use the bus more or less at the same time is when transfering files
PC->drive->8-bit computer (or the other way around). Otherwise the bus
would almost always be idle when a controller wants to use the bus.

(I use the word controller as it both describes an 8-bit computer and
also the small microcontroller interface for connecting modern
computers to IEC devices).

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