Re: [avr-gcc-list] Off topic question - 3 1/2 PC Floppy drive

[Jesper Hansen]

> The bottom line is you CAN NOT do it with a single chip anything.
>
> The 512 byte sector is only the beginning. Reading the FAT and directory
> structure of the floppy is also needed.

Well, this is not absolutely true. He didn't say WHICH format he wanted on
the disk.
Spurred by a discussion on the AVRFREAKS discussion boards recently,
I tried writing and reading raw MF data to/from a floppy using a 8515.
It IS possible, but it's quite a heavy load on the CPU.
Reading a "normal" MFM PC format is not possible, but FM data at 250
kbps seems to be doable.
Adding a logic chip or two, this could be simplified greatly, and reading
a PC format floppy should be possible.
However, it would be MUCH easier to use a floppy controller like the
WD279x, but these are not to find anymore, (except in museums and in
my drawer.  (which is basically the same ;-) ).

> Decoding the FAT table so you can read where the next sector is located.
> This is not for the faint of heart ( or programmer ).

Well, decoding the FAT is a pieace of cake. Many have done that in various
projects - see mine : http://www.yampp.com

> This is why you do not see any floppy disk controllers on embedded
systems.
> ( except x86 type )
>
> I have built floppy based systems in the old days with 6502, Z80, and
8088.
> Floppy controllers were abundant days past, but not now.

Oh, those were that days. You could almost debug code visually by just
watching
the blinking lights connected to the databus !

> Before you go running off and say " I can do this", please be aware others
> have tried ( myself included ) and we have given up.

I haven't.

>Not worth the time.

Sad, but true.

/Jesper



>
> donaldV
>
>
> avr-gcc-list at http://avr1.org
>


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