Re: Commodore 15 Second disk format routine disassembled

From: Peter Rittwage <*peter_at_rittwage.com*> Date: Fri, 19 Jun 2026 07:58:02 -0400 Message-ID: <CAJxOZi1m8V_7=eqMnjq38qQtngUWNfaMPPwsTJRXZhYyFH7bqg_at_mail.gmail.com> · peter_at_rittwage.com

That part would be easy with custom firmware on the drive, but it will
likely not be reliable. I am sure there was a reason for the other
densities.

On Fri, Jun 19, 2026 at 3:36 AM Francesco Messineo <
francesco.messineo_at_gmail.com> wrote:

> 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?
>
> IZ8DWF
>
>

-- 
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Peter Rittwage