Adding support for a new bus-master chip is actually rather easy. OWFS only
requires a few functions be supported. This is actually the point of OWFS:
the bus master and slave functions are encapsulated easily. Since we
support so many different devices, the level of abstraction is very precise.
1. Detection/configuration step. This includes any hardware configuration
and setting up the communication channel (e.g. open the serial port and
setting baud rate).
2. Sending a set of bits or bytes and reading the bus ( works for reading,
too, when sending 0xFF's ).
3. Some kind of "discovery" to enumerate the 1-wire slaves. Often hardware
assisted.
4. Optional "Power bit".
You'll also need to add a command line configuration option. If you can
describe your bus master to me, I can easily write a rough draft that you
can test and perfect. (Or send me a sample).
Paul Alfille
On Feb 18, 2015 3:59 PM, "Martin Rapavy" <martin.rap...@kistler.com> wrote:
> > Am 18.02.2015 um 21:19 schrieb Martin Rapavy:
> > > I was exactly in favor of avoiding w1 because of bus polling. It is
> > > important for me not to use the bus frequently (the wire is also
> > > shared for reading out data from sensors). Do you think that the w1
> > > polling might be turned off using w1_master_search (w1 sysfs
> > > interface)?
> > >
> > That's exactly the purpose of this node. OWFS sends an explicit search
> > command through the netlink socket to the w1 driver at
> >
> > module/owlib/src/c/ow_w1.c, line 112ff
> >
> > so turning off w1_master_search only affects other services which rely
> > on it. BUT: depending on your hardware, hot-plugging a battery may
> > already rely on this! It's a bit of a pity this is a global flag and
> > cannot be turned off by bus. Check your hardware whether it has other
> > services on another onewire.
>
> > Second pitfall: if your hardware has several buses, the w1 driver will
> > all join them into one.
> I guess this is really a deal-breaker. There really might be multiple
> buses (onewire channels) connected to that piece of hardware.
>
> > Nevertheless, patching the DS1WM w1 driver may be sufficient and easy
> > enough.
> >
> >
> > >> Option B -------- Write a fake I²C host adaptor kernel driver which
> > >> creates a new "I²C bus", with your onewire host adaptor the only
> > >> device "connected" to that "bus. This may be the easiest option if
> > >> your device behaves very much like the original DS2482. OWFS drops
> > >> in neatly, no strings attached.
> > >
> > > I like this approach but I guess I should have been more clear on
> > similarity with DS2482 -- it is conceptually similar (hardware based
> > multichannel bus master chip) but the interface is different. The
> > interface of that custom chip closely matches DS1WM.
> >
> > Then this is *not* the way to go.
> >
> >
> >
> > >> Option C -------- Memory-mapped IO from userspace, which is *UGH!*.
> > >> See module/owlib/src/c/ow/ow_ds2482.c for all the things to write
> > >> and change. The disadvantage is owfs has to run as root to do
> > >> MMIO.
> > > I don't mind running under root. I suppose this is the only feasible
> > > option if I don't want to use Linux w1. I will have a look into that
> > > source.
> > >
> > Well, if you don't show it to anyone... (^__^);
> I'm aware of non-reusability of that solution but on the other hand also
> quite specific piece of hardware and from your selection of choices I don't
> see any other way. Am I right?
>
> Best regards,
> Martin
>
> > Kind regards
> >
> > Jan
>
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