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From: dwl10@amdahl.UUCP
Newsgroups: comp.sys.cbm
Subject: Re: 1750 & C-Power 128
Message-ID: <15454@amdahl.amdahl.com>
Date: Thu, 1-Oct-87 13:01:03 EDT
Article-I.D.: amdahl.15454
Posted: Thu Oct  1 13:01:03 1987
Date-Received: Sat, 3-Oct-87 06:31:44 EDT
References: <467@polyslo.UUCP> <15298@amdahl.amdahl.com> <967@csustan.UUCP>
Reply-To: dwl10@amdahl.amdahl.com (Dave Lowrey)
Organization: Amdahl Corporation, Houston TX
Lines: 64

In article <967@csustan.UUCP> rayz@csustan.UUCP (R. L. Zarling) writes:
>In article <15298@amdahl.amdahl.com> dwl10@amdahl.amdahl.com (Dave Lowrey) writes:
>>C-Power's shell resides in memory from $0801 to $17ff. Programs that
>>run under the shell are loaded starting at $1800. No room to add
>>any code.
>
>I did a disassembly of the C64 shell a year and a half ago.  There *is* some
>room for expansion.  The region from $0801 ends somewhere short of $17ff.
>Then there is some storage which extends up to $17ff.  There is room for
>expansion between the code and storage.  Sorry, I don't remember how much
>right now.  It wasn't a lot...
>
>Also, there was a lot of code which could be quite trivially shortened and
>improved.  I opened up a *lot* of space for expansion by rewrites of
>existing code.  Of course, you need a good symbolic disassembly to start
>doing things like that.

I beg to differ, but there isn't much spare room above the shell
code.

Brief shell memory map:
$0801-$1677 - Shell code
$1678-$16c8 - Command input buffer
$16c9-$1749 - Buffer used by s/f/printf library routine
$174a-$179a - Buffer used by library routines to buffer keyboard input
$179b-$17ae - Cmd parm pointers
$17ad-$17c7 - File neame for re-directed I/O
$17c8-$17db - Name of currently loaded program
$17dc-$17e6 - Buffer for disk status message
$17e7-$17f6 - I/O status buffers
$17f7       - Current offset into kbd buffer
$17f8-$17f9 - Number of chars in kbd buffer
$17fa       - "SYS" device number
$17fb       - "SYS" drive number
$17fc       - "WORK" device number
$17fd       - "WORK" drive  number
$17fe       - stdin file number
$17ff       - stdout file number
$1800-$cfff - User's programs


As you can see, not much room to spare. You could indeed re-code some of
the existing shell code. Perhaps even eliminate some, such as "rm", "mv",
and such (you still have the "disk" command that can do the same thing).

There is even a routine, from $14eb-$1506 that doesn't seem to be called
by anyone else.

So, if you feel up to the challange, go ahead an try to add the RAM-DISK
code. But it won't be easy. If you want, you can just lend me your REU for
a few weeks, and I will try  :-).
-- 
-------------------------------------------------------------------

                  "Familiarity breeds attempt"

                          Dave Lowrey
                          Amdahl Corp.
                          Houston, Texas
                          (713)-850-8828
                         ...!{ihnp4,cbosgd,hplabs,oliveb}!amdahl!dwl10

[ The opinions expressed <may> be those of the author and not necessarily
  those of his most eminent employer. ]