Re: Commodore 15 Second disk format routine disassembled

From: groepaz <groepaz_at_gmx.net>
Date: Fri, 19 Jun 2026 13:50:12 +0200
Message-ID: <1991725.eGJsNajkDb_at_zweitrakete>
Am Freitag, 19. Juni 2026, 09:34:14 Mitteleuropäische Sommerzeit schrieb 
Francesco Messineo:
> On Fri, Jun 19, 2026 at 12:37 AM Maciej Witkowiak <ytm_at_elysium.pl> wrote:
> > In its extended format disk the disk will have tracks 35-41 formatted and
> > it reports 840(!) free blocks.
> > 
> > It not only formats the inner tracks, but, if I got the disassembly right,
> > the whole disk is formatted with the same density as tracks 1-17, with 21
> > sectors on each track. I'm not able to reproduce this in VICE or YaPe. I
> > don't have a real 1551 to check how reliable this is either, but indeed
> > it works on emulated Pi1551.
> and how does it configure the clock divider to allow 21 sectors on the
> smaller tracks?

The density config is independent from the track. The problem here is that the 
faster/more dense setting becomes less reliable on the inner tracks (which is 
why it exists in the first place)

That said, as for making this work in VICE - or any other emulator for that 
matter - it will probably not work on most of them, most implementations i 
have seen do not actually allow to write at arbitrary density. Or at least, 
they can't produce a correct image after that. HOXS64 might be able to do it 
IF you use g64 (it converts to flux stream internally). In VICE it should work 
if you use p64 instead.


-- 

https://cc65.github.io            https://rr.pokefinder.org
https://vice-emu.sourceforge.net  https://magicdisk.untergrund.net

Wer Ficken super findet hat noch nie was anstaendiges gegessen. 
<Jihad/Hitmen>
Received on 2026-06-19 13:00:01

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