read this carefully it may save a disk some day. i'm about to tell you a secret about the 1541 that you may have heard about before in some of those inside dos books.
as you might already know the 1541 is composed of 3 parts theres the code for a hi level comand interpreter which knows what to do for commands i,s,r and a few others. then theres level 2 which knows how to read,write,extend and poison files. level 2 and level 3 have many bugs in them most of which cause poison disks. a simple way to see this is to scratch more then 3 files in a row and then try a save&replace. now try to read the most recent file written to the disk before the scratches and it will have had a few of its sectors over written by the s&r file. the same thing will occur with a few other of the level 3 s,r commands.
a little note to young hackers
All of you 5 year old's out there remember, next time you write an operating system to be careful and write lots of little modules that can be tested and debuged instead of 16k of jumping around in mainline,irq and nmi monster routines which never seam to end, but instead just run on into something else.
level 1 will be the most useful to any one contiplating writing an improved operating system. it's the monster code which reads and writes sectors to disk memory. in the stuff i've read it's been called the job que.
the job que is how the dos reads sectors. it simply puts a comand followed by the track and sector into the job que memeory and off goes the drive. job que memory is composed of 3 bytes per memeory buffer. yes there more that one place to read sectors into. In fact there are 5 sector buffers in the drive
heres the break down
job que buffer
0000 command 0300-03ff
01 command 0400-04ff
02 command 0500-05ff
03 command 0600-06ff
04 command 0700-07ff
05 i havent used it it
06 track 0300-03ff
07 sector
08 track 0400-04ff
09 sector
0a track 0500-05ff
0b sector
0c track 0600-06ff
0d sector
0e track 0700-07ff
0f sector
with this you can read and write sectors using only the m-r and m-w commands
i'll upload a program in a few day's which will be the bios of my new os it will contain the routines to read and write sector an a heck of alot more when i feel like using all the features of the routines i wrote.i'll also give the specifics of how to use all of it.
i've used all of these thing's in my forth system and they sure do work. one last thing the only secondary thats used is 15 and due to the way things work it never has to be opened. you can just tell it to talk and listen.
finally if any of this intrigues you let me know i'm going to need all the people i can get to test the "public domain operating system one" which i will distribute as freeware. Since thats the only way I figure it might gain acceptance.
bye for now
irwin r. shapiro
as this is freeware if you feel it is helpful or it fills a void between what you have and what you want let me know and send donation if possible.
you can reach me via the following:
this sig.
compuserve mailbox 73145,130 .
western union easylink telex II 9103338689 (irssi) .
western union easylink mailbox 62803073
or simply my mailing address.
irwin r. shapiro, psc 1 box 8189, homestead, fl 33039
