bwk@mitre-bedford.ARPA (Barry W. Kort) (09/14/88)
I have Digitalk Smalltalk V/286. It runs fine on a Zenith 248 AT (IBM clone). But I cannot run it on my AT&T PC 6300 Plus. My Plus has 1 MB of RAM on the motherboard, and another 4MB of extended memory. I have tried all combinations of command-line parameter settings, but nothing seems to work. Can anyone offer some insight into the problem or suggest a fix? Many thanks. --Barry Kort
jr@amanue.UUCP (Jim Rosenberg) (09/18/88)
In article <39875@linus.UUCP> bwk@mbunix (Barry Kort) writes: >I have Digitalk Smalltalk V/286. It runs fine on a Zenith 248 AT >(IBM clone). But I cannot run it on my AT&T PC 6300 Plus. I've only used Smalltalk V/286 lightly, so I'm only guessing. ST/V 286 uses protected mode, which means it has to be switching in and out of protected mode constantly. The designers of the 286 thought they were building the Great Shell in the Sky's gift to multitasking, so they made it impossible to switch from protected mode to real mode. The reasoning was quite sound, actually: if you can switch under program control from protected mode to real mode this could be a security hole in a multiuser operating system. (So why didn't they just make it privileged??) The details on how one actually achieves a switch from protected mode to real mode are almost too gross to even contemplate. The CPU farkles some bits in the CMOS and actually *RESETS* the CPU chip!! At some point this involves sending data to the *KEYBOARD*. (Come on now, could I have made this up???) When the CPU is reset (can you spell context switch take forever?) it sees from the CMOS setting, Oh, this isn't a real reset. The whole thing does work, but just barely. The problem comes if the interface between the CPU and keyboard is not completely 100% AT compatible. Although I'm only guessing, I would bet this is the problem. The 6300+ is a strange beast, and was never designed as an AT clone. Do you have any other software that does work that you know is switching between protected mode and real mode? You're also guaranteed to have trouble if the 6300+ does not have CMOS that it addresses the same way as a genuine AT. Methinks you may be completely out of luck. (Apologies that this message has nothing to do with Smalltalk; follow-ups should probably be directed to comp.sys.ibm.pc.) -- Jim Rosenberg CIS: 71515,124 decvax!idis! \ WELL: jer allegra! ---- pitt!amanue!jr BIX: jrosenberg uunet!cmcl2!cadre! /