On Tue, Oct 06, 2009 at 06:59:24PM +0200, Oliver Hartkopp wrote:
> Marc Kleine-Budde wrote:
> > Kurt Van Dijck wrote:
>
> >> I planned to do just a 'proof of concept'. Like, the PCA82c251 has a slope
> >> control resistor, that I don't know the exact formula is, but that resistor
> >> controls the maximum baudrate. I was just making space to implement the
> >> formula.
> >> To extend the concept, I'm working on a tja1041 too, altough I never
> >> used this one before.
> >> What I want to know from this tja1041 or similar is: What pins are usually
> >> connected to the cpu, what pins are usually not, and what pins are
> >> sometimes connected. This allows me to provide a 'minimum required' set
> >> of gpio the transceiver driver needs.
> >>
> >> I _assume_ the wake pin is mostly not connected to the cpu, but direct
> >> into the power circuitry. What can a linux driver do with the wake pin?
> >
> > it can generate an interrupt that wakes up the whole linux system from
> > suspend to ram. Imagine a fast booting concept in the automotive
> > environment.
>
> Yep. The 'wake' pin is some kind of additional input to wake the system not
> only by detecting CAN traffic. E.g. you could attach a RTC or something else
> here ...
You mean the 'wake' pin from power circuit here?
I (and Marc too, I guess) meant the 'wake' output from the TJA1041
>
> Please check the schematic on page "15 of 26" from
>
> http://www.nxp.com/acrobat/datasheets/TJA1041_6.pdf
>
> This is the common application for fault tolerant transceivers that support
> the sleep modes.
>
> You need to set EN and /STB in order to set the transceiver into the sleep
> mode - see table 4 in chapter 7.1.
>
> Usually EN and /STB are both set to 1 (or open collector) and when you want to
> go to sleep, you need to perform the steps
>
> 1. Set /STB and EN to 1 (default)
> 2. Set /STB to 0 and EN to 1
> 3. Set /STB and EN to 0
>
> And then the INH line switches to off and kills your power supply :-)
>
> Our system makes a usleep(500000) (to wait for power loss) and then executes a
> system reset, e.g. when CAN traffic just re-appeared and the INH line did no
> do it's job.
>
> So for the TJA1041 we would need:
>
> EN, /STB and /ERR to be connected to the CPU via GPIO.
all 3. ok.
>
> A real goodie would be to connect /ERR to an interrupt line that also detects
> state changes - but this is not really needed.
I figured that an interrupt would come handy.
>
> I'll take a look on other 'intelligent' transceivers, if there are any
> requirements that exceed the described TJA1041 / TJA1054 needs.
My proof of concept is basically a new device class, can_transceiver,
which should enable people to develop drivers for other chips. When new
functionality arises, the class should be extended then. And it should
not be too hard.
Those are the goals.
>
> Regards,
> Oliver
>
Kurt
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