Date   : Sat, 25 Nov 1989 16:45:05 GMT
From   : ubc-cs!alberta!calgary!amc-vlsi!willy@beaver.cs.washington.edu (William Gonnason)
Subject: ZSID question

I don't have a copy of ZSID, so you may have to take the following analysis
with a grain of salt.  However, it's not too different in syntax from
some other CP/M debuggers I've used...  With the previous warning in mind,
here is my analysis of your batch file:


       ZSID PROG.COM      - invokes ZSID (Symbolic Debugger for Z80 ) and
                            loads "PROG.COM" to transient Program Area
                            (typically 0100H on conventional CP/M systems)
       A80                - assemble the following code beginning at address
                            0080H

       LD HL,6100        \
       LD DE,6200         \  Relocates a large block of memory (I would
       LD BC,6001         /  suspect the BIOS... ???)
       LDDR              /   (ie, shift 6001H bytes down by 0100H (assuming
       NOP                   the default assembler base is hexadecimal!)
       NOP
       .                  - end of code...
       P8B                - got me, but I think this sets a breakpoint in ZSID
                            at location 008BH, returning control to ZSID when
                            address 008BH is encountered.  It would appear to
                            prevent the need for a "RET" instruction in the
                            assembly code segment...
       G80                - execute code stating @ 0080H
                            ( effectively a jump, which will relocate memory,
                            then return control to ZSID... )
       IPROG.COM          - set up File Control Block for filename "PROG.COM"
       R                  - read in file set up with previous "I" command

       GO                 - execute program in TPA without reloading it
                            (usually, this is effectively a JMP to 0100H )
                          - GO is a CCP command, meaning that you
                            have exitted ZSID somehow between the "R"
                            command and the "GO" command, although I don't
                            see how (perhaps an embedded ^C in the batch
                            file ???)

       SAVE 32 CPROG.COM  - save 32 pages starting @ 0100H to the
                            file "CPROG.COM" (one page being 256 bytes)
                          - "SAVE" is also a CCP command, which makes
                            me sure you have left ZSID by this point...

The code is quite likely a quick and dirty way to read in a program,
offset said program (somehow) and then write it out again.  However,
it sure plays hell on absolute addressing schemes...  But, I can't offer
any more information than this.  Perhaps someone else on the net?


- OS/2 - the other half takes EVEN MORE RAM ... [ willy@amc-vlsi.CA ]
 OS/2 - the other half takes EVEN MORE RAM ... [ willy@amc-vlsi.CA ]


End of INFO-CPM Digest V89 Issue #206
*************************************