On 2013-05-08, at 11:53 PM, Guenter Roeck wrote:
> Guess the real conclusion is that one should avoid two active masters
> in the first place if possible.
I agree, I can't think of any benefits worth the trouble.
> Is one of the I2C adapter drivers your own ? If so, you can disable auto-detection
> in the adapter code by setting the adapter class to 0 (specifically, don't set it
> to I2C_CLASS_HWMON). You can do the same in the Kontron driver if you have the
> source (it is GPL so you should be able to find it). While not perfect, that should
> be better than disabling auto-detection in the affected chip drivers.
That's great advice!! I will look into this, thanks!
> Note that the Kontron driver also sets I2C_CLASS_SPD, which means EEPROMs are
> auto-detected on address 0x50.
Funny, I had to explicitly inject "I2C_BOARD_INFO("24c32", 0x50)" to see
Kontron's JIDA chip.
>> [...] Right now I have a working setup where some slaves are
>> declared on bus 0 (PLD i2c master) and others on bus 1 (FPGA i2c master). I have
>> yet to stress test the setup within the next day or so, but so far, it seems to
>> work ok.
>>
> Sure, it does work, I am just not sure what the benefits are of having two
> masters in this scenario.
My thoughts exactly. I would have avoided it. Right now I am trying to improve
and existing design.
> Guess you are saying that the I2C master in the
> Kontron PLD can not drive the AD7147 - is that correct ?
Well no, it does drive it, we have it in stable production. It's just that when
you have your finger on the wheel, CPU usage goes up to 5-15%. More intense
polling of the sensors also takes a toll on the CPU. For different reasons other
than the ad714x, the FPGA i2c core option suddenly became attractive.
> If so, and if that
> means you have to use your own I2C core anyway, why bother using the Kontron
> PLD's I2C bus to start with ? You could just ignore it (ie not instantiate
> or build it at all) and use your own.
Yeah, we already considered that... our FPGA's reset and flash select are
controlled by an i2c I/O expander! Hehe, so this I/O expander needs to be
mastered from the kempld. Reality is a bummer ;)
>
> Did you tell Kontron about the problems with their PLD ? Maybe they have a
> solution.
Yes we did. If I remember correctly, the problem is the absence of an interrupt
line from the PLD to the CPU, which explains the high CPU since the driver
sleeps-polls for async PLD completions and statuses. ... I know...
Thanks for the reply!
Cheers,
/jfd
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