Date   : Fri, 17 Feb 1989 19:10:05 GMT
From   : pyramid!athertn!paul@lll-lcc.llnl.gov (Paul Sander)
Subject: CP/M-Plus Disk Access

A while back I posted a question on how to access a disk directly via the
CP/M-Plus BIOS on a banked system.  Several people replied, discussing the
"Direct BIOS Call" BDOS function (number 50).  Many thanks to those people.

However, I am still having problems setting up a buffer properly.  To
perform a disk access (say, a READ for this example) I make the following
calls to the BIOS via the BDOS:  SETBNK, SELDISK, SETTRACK, SETSECTOR, 
SETDMA, READ.  The result is that floppy drive turns on briefly, then turns
off, and the buffer I specified by the SETDMA call does not contain data
that I know are in the disk sector I specified.

The buffer I am trying to set up is not in the shared memory area, and I
get the feeling that the data are being copied into the wrong bank, and that
I'm very lucky not to have CP/M crash on me.

Here are my questions:  Am I really setting up this access properly?  If not,
what am I doing wrong?  Also, the reference I am using mentions the existence
of a "System Control Block" which contains a bunch of useful information,
and it also describes a BDOS function that returns the address of the block.
Does anyone know what the format of the System Control Block is, and could
they tell me what it is?

I've contacted the vendor of my CP/M implementation, and they no longer
carry DRI's Programmer's and System Guides.  DRI has passed CP/M support on
to a firm called Alexander and Lord, but they demand $350 for the manuals I
need (a price which I am not willing to spend right now).

Any help you can give me would be much appreciated.
-- 
Paul Sander        (408) 734-9822       | Do YOU get nervous when a
paul@Atherton.COM                       | sys{op,adm,prg,engr} says
{decwrl,sun,hplabs!hpda}!athertn!paul   | "oops..." ?