I2C drivers (for AMBA)

Hi. I am working on a custom design that is based on ARM926EJ and AMBA
bus. OS of choice is uCLinux, patched with RTAI for RT performance. I
have to implement now I2C support, but looking at the existing driver
things seem a bit unclear for me.

Here is what I unserstood:
i2c-core.c is independent of the bus and is kernel module. This should
be working. But  what about AMBA bus? Is it supported? Is this file for
support of AMBA located in 'busses' directory? What are algos files? As
I undersand, these are bus dependent. Is AMBA supported by these?

If there are not, does anyone have idea how these can be written?

How can a proper working of I2C be tested? Can some dummy I2C
peripheral be created in Linux?

Also, if you have any eperiance with I2C linux drivers, please share
it. I do not know much about these, so any links to documentation abuot
writing these drivers, or explanation how they work will be more than
helpful!

Thanks,
Drasko

http://lwn.net/Kernel/LDD3/

That book should have pretty much everything you need to know about
Linux device drivers. If you want more beyond that, perhaps pick up
"Understanding the Linux Kernel," but I don't believe that one is
online (well worth the money, however).

Brian

I suggest also to look at http://www.lm-sensors.org/wiki/Documentation.

In the picture you can find the relationship between the various
modules.

In your environment you probably will have to write the algo part (I
guess that you have an i2c
adapter connected to the amba bus with registers to access i2c
functionality).
The algo-bus split is used when adapters share some common parts (like
the bit-banging adapter).


Ale

pmst wrote:
> I suggest also to look at http://www.lm-sensors.org/wiki/Documentation.
>
> In the picture you can find the relationship between the various
> modules.
>
> In your environment you probably will have to write the algo part (I
> guess that you have an i2c
> adapter connected to the amba bus with registers to access i2c
> functionality).
> The algo-bus split is used when adapters share some common parts (like
> the bit-banging adapter).
>
>
> Ale

pmst,
thanks for the waypoints.
ARM has Amba Peripheral I2C Bus Controller (ApI2c), which I guess is a
bridge between Amba and I2C (which comes out of the chip on two pins).
So, can you tell me:
1) what abot 'buses' part? It has to be dependeant on Amba?
2) what about 'chips part? Does it have to depend on ApI2c?
3) Do I have to write only adapter part -- is this the peice of code
that is ApI2c dependant, and not 'chips' part?

I am still not clear which part of driver ('algos', 'busses', and
'chips') depends on what... And waht of existing I can use and what I
have to write by myself.

Cheers,
Drasko

drasko <drasko.draskovic@gmail.com> wrote:
> Hi. I am working on a custom design that is based on ARM926EJ and AMBA
> bus. OS of choice is uCLinux, patched with RTAI for RT performance. I
> have to implement now I2C support, but looking at the existing driver
> things seem a bit unclear for me.

> Here is what I unserstood:
> i2c-core.c is independent of the bus and is kernel module. This should
> be working. But  what about AMBA bus? Is it supported? Is this file for
> support of AMBA located in 'busses' directory? What are algos files? As
> I undersand, these are bus dependent. Is AMBA supported by these?

> If there are not, does anyone have idea how these can be written?

> How can a proper working of I2C be tested? Can some dummy I2C
> peripheral be created in Linux?

> Also, if you have any eperiance with I2C linux drivers, please share
> it. I do not know much about these, so any links to documentation abuot
> writing these drivers, or explanation how they work will be more than
> helpful!

The OpenCore I2C driver with Wishbone interface has now a driver excepted in
the official kernel:

> See link for more info:

> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=history;f=drivers/i2c/busses/i2c-ocores.c

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

1) The bus part is were I would implement the support for ApI2C, Linux
     has support for AMBA bus (as I see in drivers/amba)
2) The chips part is bus-independent and handles devices (i.e. slaves)
    connected to the  bus.


I would start off with something like i2c-ali* or i2c-s3c2410 as a
starting point/example to follow.


Cheers, Ale

FYI, a couple more links that are more Linux/I2C specific:

http://www.linuxjournal.com/article/7136
http://www.linuxjournal.com/article/7252

Brian

Thanks all for support!

As I see for now,  I'll have to write 'busses' part of the driver to
suppport ApI2c interface. I gusess some kind of simple alogorithm will
be implemented within it. I'll check out existing code and try to
figure out something.

Maybe someone would know which bus adapter from 'buses' directory can
be godd for a start (that it resembles ApI2c, so can be easily
rewritten)? pmst sugessted i2c-ali* or i2c-s3c2410, but did not say
wahy these two...

lm-sesnors have several userspace tools for checking I2C functionality,
so this can be used as a rudimentary testing base...