Re: [hatari-devel] Re: ACSI issue with Hatari

[Thomas Huth <th.huth@xxxxxx>]

Am Fri, 21 Nov 2014 23:09:58 +0000
schrieb "Konador, Cyprian" <cyprian.konador@xxxxxx>:

> 
> 
> > From: Troed Sangberg
> > Sent: 3 October 2014 19:39
> > To: hatari-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [hatari-devel] Re: ACSI issue with Hatari
> >
> > > first, then the higher address. So this driver has definitely a
> > > bug.
> > >
> >>  I think this just works "by accident" with other emulators and
> >> real
> > > hardware, e.g. because in real hardware there might be a small
> > > delay within the device or so.
> > Well. If it works on real hardware then that is the expected
> > behaviour and there's no bug in the driver. (semantics, but
> > important) /Troed 
> 
> Roger Burrows just has thrown light on that case:
> http://dev-docs.atariforge.org/files/ACSI_DMA_Guide_6-28-1991.pdf
> 
> DMA CHIP ANOMALY - It is possible to get a double strobe from the DMA
> chip it the DMA Mode Control Register is not written to immediately
> after the DMA Data Port. For this reason. while writing to the DMA
> Data Port it is necessary to write the DMA Mode Control operation for
> the next operation. This can be done by writing a long word to the
> Date Port with the data in the upper word and the next operation in
> the lower word.

That's a good reason for writing both registers at the same time. But
you still have to do it the right way. That driver did it the wrong way
(it did not write a value for the next operation to the DMA mode
control register, but for the _current_). So it likely also
failed on real hardware in certain cases.

 Thomas