Re: Z-Link hangs on my ][c

[zcaa1122@rpool8.rus.uni-stuttgart.de (Wulf Hofbauer)]

In article <2k9nll$qr7@jadzia.csos.orst.edu>,
Critical Mass <daye@CSOS.ORST.EDU> wrote:
>In article <CLIGEs.2p9@darkside.osrhe.edu>,
>phil cloud <pcloud@aix1.ucok.edu> wrote:
>>Zlink does NOT work on ][c.  (lets see if I can find the file )
>
>I know for a fact this is NOT true.  I ran Zlink on a //c (dunno the exact
>ROM revision, but it had the memory expansion under the keyboard) for several
>years with NO problems what-so-ever, and if I ever get up to see my cousin
>(who now has the beast :), I'm sure it still runs just fine.

I can't imagine why my two //c's should be different from the rest, but these
are my experiences:

I've tried two versions of ZLink (don't know the release dates now, sorry)
on both a ROM 1 (original) and ROM 2 (UniDisk 3.5) //c. In every case, the
program crashed with a System Error of 1 (unclaimed interrupt).

I've disassembled the interrupt handlers to determine the problem.
The following analysis is from memory:

When trying to send a character, ZLink reads the ACIA status register and
waits until the transmission of the previous character has completed.
Reading the status register however clears the IRQ detection bit of
the ACIA. Thus, if the receipt of a character coincides with an attempt
to send one, an interrupt will be generated, but the status register will
have been read before the IRQ handler is called.

The only way to get around this is to use some tricky scheme when reading
the status register. It essentially disables interrupts and calls the
IRQ handler manually if an IRQ would have been imminent at the time the
status register was read.

The same method is used in the serial firmware of the //c, at least for
ROM revision 2 (of which the listing is included in my reference manual).

This problem isn't specific to me. I've had reports from other //c
owners on this kind of problem with ZLink. I've written a patch for ZLink
that works for me and apparently for others as well who have tried it
(though I really don't use ZLink as I don't have a modem... I've checked
it by null-modem transfers from/to a VAX and different PC's).

If you say you don't have any problems with ZLink on your //c, I must
believe it; I cannot imagine however how this should work unless you have
a different or already patched version.

- Wulf

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 ______________________________________________________
|                                                      |
| Wulf Hofbauer | zcaa1122@rpool1.rus.uni-stuttgart.de |
|                                                      |