Re: Projects that take Commodore computers to 2021

Am 14. Dezember 2021 00:18:07 schrieb Julian Perry <jp_at_digitaltapestries.com>:
> There is one difference between SEQ and PRG files when writing out that
> I've noticed. I don't know whether it has to do with filetype, or the
> secondary address used when opening the file for write, but I noticed a
> difference in the way the files are written out on the 1541 (at least).
> When SAVING a PRG file, the drive just writes out the file, only updating
> the BAM when the save is complete, and the file handle closed.
> When WRITING a SEQ file, however the behaviour is different. The drive
> fills a track with data from the file, but before stepping to the NEXT
> track to continue writing, the head moves back to track 18 (presumably to
> update the BAM).
>
> As I said, I haven't ever been sufficiently curious as to plough through
> the drive code to see whether it's a secondary address function, or a
> PRG/SEQ file type distinction that triggers this difference in behaviour. I
> suppose just writing out a seq file as a PRG filetype (,P,W) would show
> that, too: might try that later.
>
> Anyone else notice this?



That's probably Because the SEQ file is written with PRINT#, and after each
of these statements there is an UNLISTEN command to the floppy, followed by
LISTEN on the next PRINT#.

SAVE on the other hand does a single LISTEN when it starts writing, and a
single UNLISTEN at the end.

That UNLISTEN, maybe together with a track change, could trigger the BAM
update.

André