Re: [Xenomai-core] Re: CAN updates & questions

[Wolfgang Grandegger <wg@domain.hid>]

Hi Matthias,

Matthias Fuchs wrote:
> Hi Wolfgang,
> 
> Wolfgang Grandegger wrote:
>> You have to define the real CAN system clock, which is 16/2 = 8 Mhz for
>> most SJA 1000 hardware even if the oscillator is running at 16 MHz. I
>> will add some reasonable note to rtcan_dev.h
> Is there any special reason for this? Wouldn't it be more meaningful to pass 
> the SJA1000 externally applied clock frequency? I can imagine that others 
> will also run into this issue as Jan and I did yesterday ;-)

The frequency is used to calculate reasonable bit-timing parameters, not 
only for SJA 1000. It's used in a similar way in the Linux socket CAN 
driver.

>>> Then we will soon have to discuss how to deal with a rtcan_isa
>>> derivative that uses ioremapped memory instead of ports (naming,
>>> separation or integration).
>> We could add a generic device similar to ISA (or extend ISA accordingly).
> The SJA1000 isa driver is very simple - and so is the modified version for the 
> memory mapped SJA1000. I think that merging both ways of access to the 
> SJA1000 into a single driver will make the code much more dirty. I would 
> prefer different source files (= different drivers). 

I agree.

> It would be a compromise to add support for boards that use some kind of 
> indirect addressing to access the SJA1000 (address + data register) into the 
> isa and mem versions of the driver.

Fine if this could be done in a generic way. We also should add a 
generic PCI driver sooner than later.

> One more proposal: I think many (old) ISA drivers name the module parameter 
> for the ISA io port "io" instead of "isa". For the memory mapped SJA1000 
> driver, I'd like to call the parameter "mem".

Well, I cannot remember why I used the name "isa". Common is "io" or 
"port" or "ioport", indeed. "io" and "mem" or "ioport" and "iomem" would 
be fine for me.

Wolfgang.