ARPAVAX:C70:info-cpm (08/18/82)
>From G.dag@Ucb-C70 Wed Aug 18 14:20:30 1982
I have a pseudo-ccp similar to ZCPR that I am currently attempting
to enhance. I would like to allow an application program to
set a completion code (successful, fail, etc..) so that a
command language routine can determine the next command to execute.
The way my ccp replacement works is as follows:
1) The hccp (the pseudo-ccp) loader is sysgenned into
the place of the former ccp. When CP/M attempts to
read in the ccp, it reads in the loader and executes it.
2) The loader then loads a transient program that is the
actual ccp replacement. This transient program needs
to get the completion code.
I would like to get that completion code from a spot in memory
unused by CP/M, application programs, the BIOS, or the BDOS. This
pseudo-ccp also has to be portable from system to system, so putting
a byte in the BIOS won't work. I could handle the completion code
problem by putting the code in a file (argh!) and requiring the
application to open a file and insert a code. Aside from the massive
overhead, this would be cumbersome and slow.
The location in memory I need would have to be secure, so that an
inconsistency in systems won't cause a problem. For instance, if
the user prints a program, then if the print worked and the file
was printed, the command file deletes the file. You can see the
hassle (understatement here) if the flag byte was corrupted.
I think a possible solution might have the flag byte at the absolute
top of transient memory (before the ccp). The major problem would
be that large programs won't be able to overlay the ccp (as well
as not allowing my pseudo-ccp to overlay it).
Any comments or suggestions would be greatly appreciated.
Thanks,
DavidARPAVAX:C70:info-cpm (08/20/82)
>From Chapman.ES@Parc-Maxc Thu Aug 19 23:45:57 1982