Hi Wolfram,
On Mon, Feb 23, 2015 at 02:08:42PM +0100, Wolfram Sang wrote:
> Hi,
>
> On 2015-02-15 15:44, Yoshihiro Kaneko wrote:
> >From: Ryo Kataoka <ryo.kataoka.wt@xxxxxxxxxxx>
> >
> >Even if R-Car I2C received NACK, after that it might receive ACK
> >by HW auto restart. In case of that, driver would continue process.
> >If R-Car I2C didn't receive ACK, the driver would detect timeout
> >and would report NACK as -ENXIO.
> >
> >Signed-off-by: Ryo Kataoka <ryo.kataoka.wt@xxxxxxxxxxx>
> >Signed-off-by: Yoshihiro Kaneko <ykaneko0929@xxxxxxxxx>
>
> Excuse me, but what exactly is HW auto restart in this case? Is it a feature
> of the I2C slave?
I asked Kataoka-san about this and his response was as follows:
It is a feature of the i2c-rcar(H/W) master.
If system(CPU) is busy, NACK procedure may have interrupt latency.
Since the clear of ICMCR.ESG bit is delayed, i2c-rcar(H/W) may auto-restart
after NACK. Please refer to ESG bit of H/W UM section 55.3.5.
For example, this is I2C write transmitting.
1.Start / 2.SlaveAddr,ACK / 3.RegAddr,ACK / 4.RegData,ACK / 5.Stop
If No.2 has NACK and interruption has delay, this transmitting is as follows.
1.Start / 2.SlaveAddr,NACK/ 1x.auto-restart / 2x.SlaveAddr,ACK
/ 3.RegAddr,ACK / 4.RegData,ACK / 5.Stop
NACK of No.2 is invalidated by ACK of No.2x. It means recover.
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