Re: [hatari-devel] Re: Hatari floppy drive detection with EmuTOS

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 15/01/2014 20:49, Roger Burrows a écrit :
> On 15 Jan 2014 at 18:56, Nicolas Pomarède wrote:
> > approx 1.5 sec per drive to complete would match the time needed to do
> > the spin up associated to the restore command (if the head is already
> > near track 0) ; but what I don't understand yet is that the WD1772 doc
> > says it needs to count 6 revolutions (index hole) from the floppy drive
> > to determine when the spin up is good.
> >
> > But my understanding about this is that if the drive is disconnected,
> > you will never receive the index pulse, so the revolutions counter will
> > stay at "0", spin up will never complete, and restore will never
> > complete too, because it needs spin up to complete first.
> Ah, I see your point!  That's what the WD1772 docs seem to say.  Perhaps, as
> long as you have at least 1 drive connected (which is all I've tested on real
> hardware), then the FDC sees the index pulses from the _connected_ drive when
> it's trying to do a restore on the _unconnected_ drive?  In other words, the
> restore will only complete as long as at least one drive is connected.  It
> seems unlikely, but who knows?  If I don't have any drives connected, loading
> EmuTOS is going to be tricky ...

No, I don't think that the case, signals are really separated when you 
choose one drive or the other. And it wouldn't solve the case where you 
only have one drive and it still detected.

Note that to detect index pulses you normally need one drive, but also 
one floppy in it. So, there must be something else in the WD1772 (maybe 
an internal timeout), else a disk with no floppy would not be able to do 
the spin up sequence either.
Which means only drive with a floppy would be detected, which is 
obviously not the case.

By doing a restore without spinup and just testing if signal TRK0 is 
received, you can check if a drive is ON, without having to bother about 
the spin up.

But for now, I don't see what part of the doc explain how the spinup 
succeed when the drive if off or empty.


> Here are the floppy detection times (in clock ticks) from my tests:
> 1) Both drives connected
>    Time to detect presence of drive A: 258
>    Time to detect presence of drive B: 1
> The time for drive A is mostly motor spinup time (6 revolutions at approx 300
> rpm is 1.2 seconds = 240 ticks).  Drive B was obviously at track 0 to begin
> with.
>
> 2) Only drive A connected
>    Time to detect presence of drive A: 258
>    Time to detect absence of drive B:  153
>
> I looked at my docs again and the step time for step rate 0x03 is actually
> 3msec: 3*255 = 0.765 seconds = 153 ticks!  Again drive A is spinup time.
>
> Regards,
> Roger

Thanks for those numbers, they confirm the effect of the spin up 
sequence that I need to analyze better.

Regarding case 1), drive B is detected immediatly because when you 
select another drive, the WD1772 is not aware of that. So the status 
register remains with "motor on + spin up complete" (even if drive B has 
no motor running !), which means the restore command+spinup completes 
very fast on B, as the head is already on track 0 I guess.

I'm working on other parts of the WD1772 emulation at the moment, so I 
can't mix too many things at the same time in the code, I will come back 
at this spinup "problem" after.

Thanks

Nicolas