Dirk Eibach wrote:

I have spent some time designing a RTDM I2C driver based on the linux
i2c driver. It's stripped down in some aspects but porting existing
clients and adapters should be fairly easy.
For this draft I have ported the IBM PPC4xx driver, because that is what
I have here for testing.

It's my first RTDM project, so I hope I haven't messed things up too much.

Any comments welcome!

Great! I almost forgot this topic as it was quiet after my reply, but
now we even have code to discuss.

It took some time for me to understand the RTDM concepts and to understand what the i2c linux driver is doing.

Before I start looking into implementation details, it would be nice if
you could sketch the basic idea of your API proposal and the typical use
cases. Code is more explicit, I know, but it's also a bit more tricky to
grab an overview from it. Do you also have some simple demo to show how
one should use your interface?

What I grabbed so far:
 - for each I2C interface, a RTDM device is registered
 - rti2c-api.h is ought to become the RTDM I2C device profile
 - we have read/write and a bunch of IOCTLs as API

Here is a typical usecase:

  int fd;

  //open a instance of the RTDM device
  fd = rt_dev_open( "rti2cppc4xx", 0);

  // set the address of the device on the bus
  rt_dev_ioctl(fd, RTI2C_SLAVE, addr);

  // write a value to register of the addressed device
  rti2c_smbus_write_byte_data(fd, register, value);


Many common i2c usecases are packed in inline functions in rti2c-api.h so you don't need to fiddle with IOCTLs that much.

What I didn't grabbed:
 - is transfer synchronous or asynchronous?
 - can applications access an adapter concurrently?
 - what are the major differences to the Linux model?

The interface is synchronous (just like its linux pendant). Applications can access an adapter concurrently, access is serialized in rti2-core.c/rti2c_smbus_xfer by a (per adapter) mutex.

The linux implementation has not only the device driver interface but also a kernel-api. There is a i2c_driver concept, that enables you to provide device drivers for i2c (client-)devices as kernel modules. I left out this concept because I thought it does not fit the RTDM concept.
Further I left out all the sysfs stuff.

I'm looking forward to see some nice generic RTI2C in Xenomai soon(er or

Me too :)



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