PERFORCE change 63901 for review

[Marcel Moolenaar]

On Oct 28, 2004, at 9:36 PM, M. Warner Losh wrote:

> In message: <200410290407.i9T47TB4031009 at repoman.freebsd.org>
>             Marcel Moolenaar <marcel at freebsd.org> writes:
> : http://perforce.freebsd.org/chv.cgi?CH=63901
> :
> : Change 63901 by marcel at marcel_nfs on 2004/10/29 04:07:23
> :
> : 	Add a rough (i.e. sketchy) bus frontend for a new scc(4)
> : 	driver. The scc(4) driver will handle SCCs so that puc(4)
> : 	can be released from that burden. No rocket science...
>
> What's SCC?

Serial Communication Controller, the term used for controllers
capable of multiple protocols like async, monosync, bisync and
sdlc/hdlc. Both the Siemens SAB82532 and the Zilog Z8530 are
SCCs.

The intend of scc(4) is to help deal with synchronisation between
channels. The Z8530, due to its origin, uses multiplexed registers
with each register containing bits for either or both channels.
This is very nasty and requires that the otherwise independent
channels are synchronised WRT hardware access.
A secundary goal is to allow drivers for synchronous communication
to share the scc bus with uart(4) so that the SCC can be programmed
accordingly.

-- 
  Marcel Moolenaar         USPA: A-39004          marcel at xcllnt.net