Re: Potential I2C API Enhancement

[Michael Jones <mjones@linear.com>]

From what I read, I believe the eCos strategy is to return status, not error, in APIs.

With respect to SMBus, the following are typically status:

- Timeout
- Loss of Arbitration
- NACK
- OK

NACK can indicate that a slave is too busy to accept a transaction.

These are a bit orthogonal to the need for a probe API.

One option would be to add a new device type, say "smb", in addition to i2c. Then map the smb interface over the i2c internal implementation. This would create a dependency between /dev/smb and /dev/i2c.

I don't know the eCos architecture well enough to know if this dependency can be managed properly with the CDL/Configuration, etc. But if it could, it would mean the i2c API could be left alone.

Can someone comment on whether this could be done?

Mike



On Jan 21, 2013, at 10:29 AM, Tomas Frydrych <tf+lists.ecos@r-finger.com> wrote:

> On 21/01/13 17:09, Michael Jones wrote:
>> I would also like to point out that SMBus 2.0 Section 5.5.1 documents
>> Quick Command, which is composed as:
>> 
>> S | Slave Address | Rd/Wr | A | P
>> 
>> which has no data. If this were performed with i2c_transaction_tx,
>> there is no way to know with the current API if the command was error
>> free by using the return value.
>> 
>> If the i2c API could return a negative integer, -1 could be used to
>> indicate errors like NACK, arbitration loss, timeout, etc.
> 
> I entirely agree that being able to report errors through the i2c API is
> desirable, and it's one of the issues I run into when implementing the
> Kinetis i2c driver. For example, there is no way to report when the bus
> is busy, so the driver ends up just waiting for the bus to become free
> -- this is not always desirable behaviour, as discussed in
> http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001397.
> 
> Tomas