Path: utzoo!utgpu!watmath!isishq!f171.n221.z1.FIDONET.ORG!izot
From: izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh)
Newsgroups: comp.sys.cbm
Subject: Re: Can REL files be copied?
Message-ID: <2030.2442CAD5@isishq.FIDONET.ORG>
Date: 11 Apr 89 15:22:21 GMT
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 > From: dwtamkin@chinet.chi.il.us (David W. Tamkin)
 > Message-ID: <8190@chinet.chi.il.us>
 
 > One difficulty in copying relative files is that EOI (st=64) is sent at the
 > end of every record.  The only way to know when to stop reading is an error
 > 50 (record not present) from the source disk.  The other is that BASIC's
 > INPUT#, GET#, and PRINT# commands respectively untalk, untalk, and unlisten
 > the addressed device when they are done, and unlistening or untalking a
 > disk
 > drive with an open relative file bumps the record pointer to the start of
 > the next higher record.
 
   Sorry to say this, but that serves you right for doing this in BASIC. File
copying accross devices is slow enough without introducing the fun of a BASIC 
interpreter. And, as you say, the BASIC commands do things you don't want them 
to. That's always the risk when using a high-level language.
 
 > One possible algorithm is this: read the block count and record length of
 > the
 > source file from its directory entry on the source disk.  Allow for side
 > sectors and take an estimate of how many records there are (empty as well
 > as
 > used).  Try to position to that record in the source file, and if you get
 > an
 > error 50, try one record lower; if you get an ok from the drive, try one
 > record higher.  Keep going until you've had at least one 50 and one ok so
 > that you have the proper count of records in the source file.
 
   Sounds like a good technique to me. Using a record buffer (only need one 
page, since records won't exceed 255 bytes in length), an ML program could 
copy the files quickly & easily:
 
Open the files;
 
LDX INCHAN              ; secondary address used for input file
JSR CHKIN
LDY #0
while not EOI {
  JSR $FFE4
  STA BUFFER,Y
  INY
  }
STY RECLEN
JSR CLRCHN              ; untalk
LDX OUTCHA              ; secondary adderss used for output file
JSR CHKOUT
LDY #0
WRLOOP LDA BUFFER,Y
JSR $FFD2
CPY RECLEN
BNE WRLOOP
JSR CLRCHN              ; unlisten
 
Repeat that for as many records as you need;
Close the files.
 
   In this way, commas, quotes, CRs, etc. all get copied into the new REL file 
record. No intermediate untalks to foul up record pointers.
 
 > But yes, relative files can be copied.  The c: DOS command in dual drives
 > (both from Commodore and from MSD) did it flawlessly.
 
   I have dumps of those ROMs in my Toronto office; perhaps it would be worth 
seeing how they did it (it may not always be the best way, but it works well 
(therefore always a good candidate for "best" anyways).
 


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