RE: ATN trap needed for C128 as well?

Hi,

Disclaimer: I don't know what Server64 is or really the scope of
environment is your describing but I caught that there was connections to
some control lines and possible code changes.  I don't know how the PC is
connected or what function is serves from the description

Using the symptoms of C128 runs when speed booted into C64 mode and
possible runs if hooked up after booted then I would start to think of a
race condition during the initialization phases or something grabbing a
hard control line like the reset which runs everywhere.

1) Scope the reset line where it comes up to the 6502/8510 and see if it
is active and that it didn't do any kind of stutter step that that
confuses the internals of the '02.
2) Consider that lines like the NMI and IRQ are valid lines to toggle but
if they are active at the wrong time, I.E. before the MMU is set up for
example then they could result in attempting to jump to an interrupt while
memory or map is in an illegal state.
	* Check if /IRQ is already low or goes low  early after /Reset.
If you are hooking the code doesn't let a CLI get executed until the
system really is ready for an interrupt.  Sometimes this means not calling
a "normal" call too early as it may CLI so that interrupts can nest or if
something clears the mask to early.
	* Check if there is an /NMI edge way early, again the processor is
forced to jump to the NMI Reset vector and if _anything_ needed to execute
the code is missing or not initialized it could/should crash.
	* Honestly I forget the order of things, I used to be able to
trigger on something near the end of the initialization stuff but I have
long since forgotten the details.  The concern would be more of the same
if code is hooked or an interrupt and NTSC hasn't been set yet, or all of
the sources of real interrupts haven't been enabled so that you actually
cant clear an interrupt.  Check that /IRQ's are already stuck low before
crash, once times are set they could go low after the crash.   Maybe
successfully executed interrupt but didn't have anything to return to or
it is stuck processing nothing but interrupts.  One time it took 15
minutes to boot because it would execute exactly one instruction before
going back into /IRQ. (Missing pullup syndrome, how to make your system
crawl over a $.01 part)

Bil

-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Baltissen, GJPAA
(Ruud)
Sent: Thursday, February 23, 2012 9:43 AM
To: cbm-hackers@musoftware.de
Subject: ATN trap needed for C128 as well?

Hallo allemaal,


I was given a PC case made of Perspex. It is quite wide and that gave me
the idea of placing a C128 left of the drives and in such a way that all
connectors were accessible. As the C128 was placed on the left side, there
would be no room for the original PC board. But before cutting the needed
holes, I got the weird idea to exchange the side plates and turn the back
plate upside down. This still enabled me to install a PC as well!

My IEEE drive emulator originates from Server64. At that time I replaced
the IEC routines by IEEE ones. The idea rose to add the IEC routines so I
could use this PC as IEC drive emulator. I started with the original
program to make sure things worked out fine. But it didn't. two
problems: after a reset READY wouldn't appear until I disconnected the
cable and directories didn't appear on the screen as they should. (I
didn't try more things) I remembered that that happend as well when I
tried to improve the program 15 years ago. But at that time I bcame more
interested in the CBM's and decided to use for IEEE drives alone.

But yesterday evening I booted the C128 into the 64 mode by pressing the
C= key and things ran fine, but why ???

Today I had a look at CBM-HD to see what I had to change. With an
exception everything was quite low-level so I didn't forsee many problems.
The exception were the routines to de/activate the ATN trap. I first
thought about adding a line in the sprit of "if it is an IEC devive,
simply exit the routine now". But then I realised that this phenomen
looked like the problems I had with the IEEE drives years ago (that is,
IIRC). If this is indeed the case, I have to have another look at the
software to see if I can create a ATN trap there: Nick Coplin's 64HDD can
do it as well! In the worst case I have to tinker a bit with my hardware.


But I have no idea what causes the C128 NOT to start up as long as the PC
is connected. I see on the screen that Server64 goes into action the
moment the C128 has been reseted but haven't any idea yet what it is
waiting for. Anyone an idea (could save me some time)?

Many thanks!


--
     ___
    / __|__
   / /  |_/     Groetjes, Ruud
   \ \__|_\
    \___|       URL: Ruud.C64.org



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