Re: format difference between a 4040 and a 1541

It could very well be that there is a difference in gap length between 
formatting a disk and writing a sector. Those are two different code paths 
IIRC.

André


Am 28. September 2025 19:23:26 schrieb Francesco Messineo 
<francesco.messineo_at_gmail.com>:

> On Sun, Sep 28, 2025 at 6:48 PM Spiro Trikaliotis
> <ml-cbmhackers_at_trikaliotis.net> wrote:
>>
>> Hello,
>>
>> just to add a little bit to Andrés statements:
>>
>> * On Sun, Sep 28, 2025 at 02:44:10PM +0200 André Fachat wrote:
>>
>> > The dual CPU drives write 8 byte of real gap data bytes, which get translated
>> > into 10 GCR bytes.
>
> if the conversion program I'm using is doing its job, on a freshly
> formatted header, even the 4040 has 9 bytes of gap (gcr encoded).
>
> 4040 raw header:
> ; Following raw bytes:  52 57 d5 55 72 9a a6 a5 29 4a 52 94 a5 29 4a 52 94 a5
> 2b
>
> 1541-05 raw header:
> ; Following raw bytes:  52 57 95 79 72 9a e6 e5 55 55 55 55 55 55 55 55 55 55
> 55 ff
>
> (the ff should be the sector sync start)
>
> On the other hand, when a sector has been re-written after the initial
> formatting, there're differences:
>
> 4040:
> ; Following raw bytes:  52 57 25 29 72 9a a6 a5 29 4a 52 94 a5 29 4a 52 94 a5
> 10 de ff
>
> 1541-05:
> ; Following raw bytes:  52 57 75 29 72 9a e6 e5 55 55 55 55 55 55 55 55 55 55
> 52 bf
>
> It seems the 4040 waits one byte too much before starting to write the
> data part of a sector and "spoils" the start of the data sync. On the
> other hand the 1541-05 delay is consistent with the length of the gap
> used at format time.
> If I understand correctly what's going on of course.
>
> Best regards
> Frank IZ8DWF