Date   : Sat, 30 Jun 1984 11:09:04 EDT
From   : David Towson (CSD) <towson@Amsaa.ARPA>
Subject: Re: Recent query concerning MOVCPM "synchronization error"

David - Here are three messages I saved from a while ago which apply to your
recent query concerning MOVCPM "synchronization error".  If you work out the
patches to MOVCPM that will disable this feature, please let us know.  I
realize the feature was put there to prevent people from doing bad things to
CP/M by trying to move it with the wrong version of mover, but it is a
nuisance at times, isn't it.


Dave
towson@amsaa.arpa



----- Forwarded message # 1:

Received: From Brl.ARPA by BRL-BMD via smtp;  29 Jul 83 16:17 EDT
Date:     Fri, 29 Jul 83 15:56:47 EDT
From:     Rick Conn <rconn@brl>
To:       ACB.TYM@office-2
cc:       info-cpm@brl
Subject:  Re:  BDOS secrets

Hi --

1.  The first six bytes of the BDOS (before the entry point) contain the
serial number.  In CP/M systems, the serial number is contained within
the CCP and the BDOS.

2.  The four byte-pairs after the entry point are addresses of subroutines
to be executed when certain BDOS errors occur.  Specifically, these four
byte pairs have the following meanings:

       1st Pair:  Address of Permanent Disk Error routine; this
                       routine is executed when bad block is encountered
       2nd Pair:  Address of Select Error routine; this routine
                       is executed when a select to an invalid disk
                       (such as E when the BIOS allows for up to D)
                       is made
       3rd Pair:  Address of Disk R/O Error routine; this routine
                       is executed when a write to a R/O disk is attempted
       4th Pair:  Address of File R/O Error routine; this routine
                       is executed when a write to a R/O file is attempted

As a rule, these routines usually print an error message and then do a
warm boot.  Utilities may use these to trap out errors they cause and
perform other functions besides warm boot.

To summarize, the picture looks like this:

Base of BDOS:  DS      6       ;Serial Number
               JMP     BDOSE   ;Enter the BDOS at the command processor
               DW      PERSUB  ;Permanent Disk Error
               DW      SELSUB  ;Select Disk Error
               DW      ROSUB   ;R/O Disk Error
               DW      RONSUB  ;R/O File Error
BDOSE:         ...             ;BDOS command processing


       Rick

----- Forwarded message # 2:

Received: From Brl.ARPA by BRL-BMD via smtp;  30 Jul 83 20:58 EDT
Received: From Mit-Mc.ARPA by BRL via smtp;  30 Jul 83 20:52 EDT
Date: 30 July 1983 20:50 EDT
From: Ronald G. Fowler <RGF@mit-mc>
Subject:  [RGF: BDOS secrets]
To: INFO-CPM@mit-mc


Date: 30 July 1983 18:50 EDT
From: Ronald G. Fowler <RGF>
To:   ACB.TYM at OFFICE-2
cc:   RGF
Re:   BDOS secrets

1) Those six bytes at the beginning are the CP/M serial number; they 
   have little significance to anything other than the MOVCPM program
   (which disables interrupts and halts if these numbers do not match 
   MOVCPM's internal serial number).  I'm also told that some rather
   rude implementations of CP/M come with utilities that take it upon
   themselves to do this serial number check also.

2) The four vectors are pointers to the following routines (in order):

       a. Permanent error subroutine (ie, BDOS ERROR ON X: BAD
          SECTOR)
       b. Select error
       c. Disk read/only error
       d. File read/only error

   The BDOS uses these addresses to find the corresponding error-
   handling subroutine; in theory, a transient program could overlay
   this table with pointers to its own routines, and thereby circum-
   vent the unfriendly BDOS error handlers, replacing the routines
   with more human-oriented messages.  In practice, few programs do
   this; it's a risky practice, and not quite as clear-cut as it
   sounds.                     --Ron Fowler


----- Forwarded message # 3:

Received: From Brl.ARPA by BRL-BMD via smtp;  1 Aug 83 2:46 EDT
Received: From Rand-Relay.ARPA by BRL via smtp;  1 Aug 83 2:41 EDT
Date: 1 Aug 1983 01:26:05-EDT
From: goldfarb.ucf-cs@rand-relay
Return-Path: <goldfarb.UCF-CS@Rand-Relay>
Subject: Re:  [RGF: BDOS secrets]
To: RGF@mit-mc
Cc: info-cpm@brl
Via:  UCF-CS; 31 Jul 83 23:28-PDT

Have you ever noticed that when MOVCPM halts with a serial number
disparity, it prints:

            SYNCRONIZATION [sic] ERROR

This goes back as far as I can remember (version 1.?).  Maybe they 
were looking for one byte to save in MOVCPM and dumped the 'H'? :-)
                               Ben

----- End of forwarded messages