Re: [hatari-devel] TOS 3.06 does not boot from ACSI

[Thomas Huth <th.huth@xxxxxx>]

Am Wed, 5 Oct 2016 21:51:10 +0200
schrieb Christian Zietz <czietz@xxxxxxx>:

> Christian Zietz schrieb:
> 
> > Now, sadly I don't own a TT to test this theory, but I suppose that
> > the GPIO register is preserved across a reset and thus allows a
> > one-time (not permanently stored in NVRAM) boot selection.  
> 
> The huge amount of Atari data I recently browsed -- you may have seen
> parts of it at <http://www.chzsoft.de/asic-web/> -- also contains
> technical specifications of several TT ASICs. Part of it confirms my
> statement above:
> 
> | The SCU also contains two read/write registers that can be used for
> | system configuration information. Since these registers are only
> | reset at power-on, their contents can be used across reset button
> | resets.

Christian,

thanks a lot for that information. You're right of course, that
register is not a VME GPIO register, but rather some general purpose
register without connection to the outside. I was just fooled by the
"Hardware Register Listing" from Dan Hollis which lists this register
in a section labeled "VME Bus ...", but looking at the official TT
Hardware Reference manual from Atari, it is clearly also not labeled as
VME there.
So I changed the Hatari sources again and implemented it as simple
readable+writable register instead, and everything still works fine as
expected, no need to force a certain value in this register here with a
dedicated handler.

 Thomas