Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!UHHEPG.BITNET!RALPH
From: RALPH@UHHEPG.BITNET
Newsgroups: comp.os.cpm
Subject: Stack in the BIOS, and the SB180 format
Message-ID: <8805030614.AA03984@ucbvax.Berkeley.EDU>
Date: 3 May 88 03:10:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 43

Date:  2-MAY-1988 19:56:16.05
From: Ralph Becker-Szendy RALPH AT UHHEPG
To:   0::"info-cpm@simtel20.arpa",RALPH
Subj: Stack in the BIOS, and the SB180 format
Hi

I am writing my own BIOS. So far it has been quite easy (thanks to a real
smart disk controller), and the BIOS has been structurally simple.

Now the BIOS is growing (for example interrupt-driven buffered IO, and several
switchable disk drivers) and getting more complicated; that involves several
layers of subroutines in regular BIOS routines and interrupt service routines.

So far I simply ignored the problem of having enough space on the stack when
the BIOS is called; the bios will just never need more than 4 bytes for itself
(two levels of subroutines), so I just assume that whenever the BIOS is called
(regardless whether from the BDOS or from an user program) there are at least 4
bytes left on the stack, and never ran into a problem. Now I may have to use up
to 30 or 40 bytes on the stack, and I'm getting scared. So, here is the
question: Is there any generally accepted rule about how much stackspace should
be available when the BIOS gets called ? If no, what can one usually get away
with ? What are your experiences ???

I know that I can keep a seperate BIOS-internal stack, and switch stacks
whenever the BIOS is called. That is awkward (for example, it gets confusing
when one BIOS routine calls another one, or even worse, an interrupt-service
routine calls a BIOS routine !) and time-consuming (that is particularly bad
for interrupt-service routines).

Second part of the question (quite unrelated to part one): Could a kind soul
tell me about the details of the 5 1/4" disk formats usually used by:
- Heathkit H89
- Byte/Micromint SB180
- Kaypro portable.
I want ALL THE DETAILS (SD/DD, # tracks, # sectors, sector length, SS/DS,
side bits set on which side, directory length, sector skewing).

As usual, answers directly to me, i'll write a summary.

Thanks a lot in advance !

Ralph Becker-Szendy                                     RALPH@UHHEPG.BITNET
University of Hawaii / High Energy Physics Group              (808)948-7391
Watanabe Hall #203, 2505 Correa Road, Honolulu, HI 96822