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From: tilmann@mcshh.hanse.de (Tilmann Reh)
Newsgroups: comp.os.cpm
Subject: Re: BIOS Problems with Zilog Registers
Message-ID: <9115@mcshh.hanse.de>
Date: 29 Apr 91 17:31:30 GMT
References: <9104261028.AA09385@LL.MIT.EDU>
Lines: 22



Jay Sage writes:

> ... that may have been the result of failure of the BIOS to preserve the
> Z80 alternate and/or index registers.  This is a suprisingly common problem.

> We provide an extended version of the NZCOM virtual BIOS that preserves
> whatever registers the BIOS trashes.

> Some experiments with a debugger might reveal exactly which BIOS
> calls are trashing the registers, and then perhaps a patch could be squeezed
> into the BIOS.

Wouldn't it be better to fight the reason for the problem instead of the
results? As I pointed out some time ago, *NO* program is allowed to trust in
the values of *ANY* register after a BDOS or BIOS call (quoting the CP/M-3
programmers manual). So why does noone search for the error-causing passage
in UCRLZH and corrects it? (Then it would run on *every* machine, of course!)

Tilmann Reh		tilmann.reh@hrz.uni-siegen.dbp.de
			tilmann@mcshh.hanse.de