Stack Depth requirements for CP/M 2.2 CBIOS - test-drb@ccmp.vtda.org

31 Jan 2009

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Subject: RE: Stack Depth requirements for CP/M 2.2 CBIOS
   From: "ROBO5.8" <robo58 at optonline.net>
   Date: Sat, 31 Jan 2009 07:54:55 -0500
     To: "'General Discussion: On-Topic Posts Only'" <cctech at
classiccmp.org>

Hi Chuck,

Thanks for the reply.

My IDE drive is about 2GB which is overkill and beyond the capacities of
CP/M 2.2.  So I'm only using 20MB of the drive for this project.  My system
uses Interrupts for Floppy but polling for the IDE. 
Anything under 16drives of 8mb will fly (128mb) and not using the full 
drive is not an issue.

...
 In the mid 70's and early 80's I did lots of
CBIOS work and never ran into
stack problems with CP/M.  Maybe the code was simpler and I used fewer
Calls, Pushes and Pop's.

I am currently using a Private Stack for some of my CBIOS debug routines
since they are more stack intensive.

Did you find that you had to make any other changes to the
Blocking/Deblocking code other than the recommended CP/M 2.2 patches for
success? 
I'dn look at drive selection and allocation vector (alloc) for a 8mb logical
drive that nees to be at least for 4kb allocation size should be at least 
256bytes for each drive!  You can make it smaller by making the allocation 
chunks larger (8kb would only need 128bytes).

I've never had stack size issues for just disk IO but interrrupt handlers 
yes always on creatign private stack.  I generally develop the disk IO
with minimal polled IO to limit the number of things that can go wrong
and ones the disk IO is up then roll in the interrupt IO and added features.

Allison

...

Thanks Robo

-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Chuck Guzis
Sent: Friday, January 30, 2009 7:29 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Stack Depth requirements for CP/M 2.2 CBIOS

On 30 Jan 2009 at 19:08, ROBO5.8 wrote:

  I have rewritten my old systems CP/M 2.2 CBIOS to
add an IDE Drive.

 I've run into a problem that has me stumped.  Everything works as long as I
  don't try and copy or assemble a large
Assembly file (>80KB).

 I will be going along fine and then out of nowhere I will see CP/M request
 access to Drive "T".  My debug info says SELDSK is requesting Drive
0FF00h.

 I have added debug code to all the CBIOS routines so that they report what
 they are doing to the console (slow but nice).

 I've gone through my code many times and tested each routine via an embedded
  debug monitor.  I believe I have added every CP/M
2.2 patch (1-6 and 9)that
  is specific to the CBIOS including those dealing
with Blocking/Deblocking. 
What do you mean by "large"?  I've run 2.2 with disks up to 20MB with 
no problems.

CP/M's stack can't be depended upon for much space at all.  Since my 
BIOS code was interrupt driven, every interrupt service routine 
started with a change to a private "system" stack.  I recall having a 
lot of problems before doing that.

Cheers,
Chuck