Re: [hatari-devel] floppy media change on TT

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 30/05/2019 à 15:03, Christian Zietz a écrit :
> Nicolas Pomarède schrieb:
>
> > As I don't have a TT to test this myself, could someone read the content
> > of FFFA81 when a floppy is inserted in the internal drive and when the
> > drive is empty ? (I don't know if this bit is inverted before going into
> > MFP GPIP6).
>
> As promised, I did some tests on my TT. It's not the original floppy
> drive, though. I found the following:
>
> - The drive only signals a disk change on pin 34 when it is selected via
> the corresponding drive select signal.
> - If the drive is selected, it will drive pin 34 low in case of a disk
> change. Much like the other signals on the floppy drive interface, this
> is an open-collector output. A pull-up resistor is located in the TT.
> - The signal is inverted before going into the TT-MFP. Therefore, bit 4
> gets set to '1' in case of a disk change.
> - The drive will only reset the disk change signal after receiving a
> step pulse. Thus, if the head is already on track 0 and TOS just reads
> the boot sector, FAT and root directory from track 0, the disk change
> signal will stay asserted (=line low, bit '1') even after TOS has
> finished detecting the media change.
>
> Hope that helps,
> Christian

Hi

thanks for your tests ; I read a similar description about bit being 
reset only on the next step signal on PC, so this seems to be the common 
behaviour of most drives for pin 34 to keep its "ejected" value until a 
step is explicitely made (I read somewhere that it was made this way to 
be sure the host program had time to read pin 34 in case of a very fast 
eject/insert sequence)

Seeing Roger's test on his TT, where bit 4 was always 0 (ie inserted) it 
seems though that not all TT had a compatible drive with such pin 34.

I might had support for insert/eject pin34/bit4 anyway, even if TOS 
doesn't use it, maybe some programs do.


Nicolas