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From: Michael Jones <>
Subject: Re: Potential I2C API Enhancement
Date: Mon, 21 Jan 2013 17:09:00 -0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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.


On Jan 21, 2013, at 8:08 AM, Michael Jones <> wrote:

> While working with the I2C interface using Kinetis to write a SMBus/PMBus layer over it, I could not implement a probe.
> PMBus developers typically probe the bus looking for slaves by sending an address and using ACK/NACK to determine presence.
> The only way one can probe with the current I2C API is to send at least one data byte, so that the return is an indicator of success or failure. However, this is a dangerous way to probe, because it might have side effects.
> Sometimes people probe with Addr+Read, but most use Addr+Write, because that avoids a potential ARA response.
> I am looking for ideas how best to deal with this problem. Potential solutions:
> 1) Use a target specific API
> 2) Add to existing API, like i2c_slave_present(...
> 3) Add new API/Package
> In my opinion, choice 2 would be the best because it is target independent, and least confusing.
> The practical impact is people developing SMBus/PMBus tend to use Cortex M. There are a small number of targets (5) in the dev tree. So perhaps it is still possible to add to the I2C API?
> Thoughts?
> Mike

  reply	other threads:[~2013-01-21 17:09 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-21 15:08 Michael Jones
2013-01-21 17:09 ` Michael Jones [this message]
2013-01-21 17:29   ` Tomas Frydrych
2013-01-21 19:53     ` Michael Jones

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