Re: Address of second TMSCP controller

[Johnny Billquist <bqt%update.uu.se@localhost>]

On 2021-01-26 16:56, David Brownlee wrote:
> On Tue, 26 Jan 2021 at 15:20, Anders Magnusson <ragge%tethuvudet.se@localhost> wrote:
> > Den 2021-01-26 kl. 16:05, skrev Paul Koning:
> > > > I imagine you could add a second mtc line to your config at whatever
> > > > address you put your Dilog card at.  ISTR that DEC had a bunch of rules
> > > > for such addresses - the phrase "floating CSR space" comes to mind -
> > > Right.  In the DEC rules, this is a "first unit fixed, rest float"
> > > device, just like the MSCP disk controllers.  The float CSR rank is 30.
> > > Does NetBSD do the floating CSR address algorithm?  If not, yes, just
> > > pick some address and tell the OS what it is.
> > No, NetBSD do obey the floating CSR spec.
> > This code is actually from 4BSD which didn't either.
>
> Is it just a matter of adding mtc* lines to the config for the 2nd and
> subsequent floating address - or is there some risk of false positives
> if a different device is at that address?

To do it properly, you cannot at all use the config lines as NetBSD have 
it today.
But yes, you can add additional lines for mtc with other CSRs. But there 
are limits to how well devices can be probed, so if you have something 
else on that address, it might be a false positive indeed.

The whole point of the DEC defined floating CSR configuration rules was 
in order to reliably identify each controller type. But it requires a 
rather more intelligent contextual probing of the address space instead 
of the NetBSD rules based matching system.

  Johnny

--
Johnny Billquist                  || "I'm on a bus
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