Subj : OT: horrible 8086 segmentation
To   : All
From : mm0fmf
Date : Mon Nov 25 2024 17:33:37

Raspberry Pi relevance : I'm writing some Pi Pico code


I was doing some head scratching when I remembered I'd written something
very similar in the distant past to what I was doing. I had to dig
through piles of CD-Rs to find the one with the backups on from all
those years back. It still reads fine, 21st July 1998 is the date on the
CD. 26 years old.

Anyway, I've pulled the files from it on to the wee Linux machine for
updating and use in the project. There's a date in the header saying
"created 1993" and last changes were "16th July 1996". I was just
starting to go bald then!

I've been rummaging through this old CD-R looking at what I was up to
all those years ago and found all sorts of horrible 8086 segmentation
management in the C code

e.g.
"
     // start of barrel
     EventRec far* searchp = (EventRec far*) work.bufs;

"


My eyes! My eyes! That was COMPACT model code, so 64k of code and 1MB of
data, code addresses were 16bit offsets to the CS reg and data was far
so 32 bits of segment and offset of DS or ES. And of course you had to
be extra careful of any pointer arithmetic as a far pointer wrapped
after 64k. You had to use slower HUGE pointers to get automatic
normalisation. God it was shit.

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