Date   : Mon, 15 Apr 1985 22:05:23 GMT
From   : maxwell%eiffel.dec@BRL-TGR.ARPA
Subject: CP/M BIOS blues...

[This line has bugs.... >0OO OO0<]

Hep, ah say, hep me!!!

I  finally decided to replace my *old* upwards from CP/M (tm) 1.4 compatable
Xitan  ELDOS 'operating system' with CP/M 2.2. I wrote a BIOS, including the
guts  of  the ELDOS driver for my Xitan DDDC disk controller, and tested it.
Parts  actually  worked.  I then tried to create a system disk with CP/M 2.2
and my new BIOS and learned, much to my horror, the result was *too big*.

I  realize  that I could just increase the system tracks to 3 from 2, giving
more  room, but I've got a lot of software (150+ diskettes) that assume data
(directory) starts on track 3, so....

[Bright  idea,  after  much  gnashing  of teeth, pulling of hair, renting of
clothing,  although  I now realize that others (Heathkit) have done it, too]
"I'll  put  the CCP in a file (CCP.SYS), BDOS and BIOS on the system tracks,
and  have  the  cold  and warm starts load the CCP from disk using BDOS file
I/O. That'll give me plenty of room."

Soooo,  I  modify  the  BIOS  boot  to call BDOS to open CCP.SYS, read in 16
records, and presto, the CCP is loaded, right?

Wrong.  For  some  unexplained reason, no data is transferred. DDTing though
the  BIOS  I  find  that  a) CCP.SYS is opened just fine (FCB modified, disk
accessed,  no errors returned, an' ever'thing) but b) when BDOS is called to
read each record, no disk activity occurs although BDOS returns with 0 in <A
(that's  register  A,  for  all  you ZBUG fans), saying everything's kosher.
Balderdash!!!

If  I've  managed to leave the CCP in place (after DDTing old CPM.SYS), CP/M
executes normally, impling that my BIOS is alright, and that BDOS is alright
(I  can  execute STAT.COM and other .COM's, TYPE files, etc.). However, if I
zap  the  CCP before executing the warm start, BIOS thinks it loaded the CCP
from CCP.SYS and tries to execute garbage.

I  *must*  be  doing something wrong, but what? Help. ELDOS is too large and
too  old  to  continue  using,  and  I  need  CP/M  2.2 to continue using my
tools....

-+- Sid Maxwell