I2c producing crazy console messages [[Re: insanely-high interrupt rates -- PARTIAL resolution (Pi2)]]

[Per Hedeland]

On 2019-04-19 18:04, Ian Lepore wrote:
> On Fri, 2019-04-19 at 13:32 +0200, Per Hedeland wrote:
>> But anyway I would be *extremely* surprised if I saw them, since
>> AFAIU
>> the i2c bus per se has no concept of interrupts - you need to connect
>> some other wire from the device to e.g. a gpio pin (with appropriate
>> config) in order to generate interrupts - and I haven't done that.
>> (The
>> ads1015 does have an ALERT/RDY pin that could potentially be used for
>> it, but since FreeBSD AFAIK doesn't have a way to deliver the
>> interrupts to userland code, I had no interest in it.)
> 
> You're thinking about this all wrong.  The interrupts have nothing to
> do with the i2c bus, but the i2c controller still uses interrupts to
> signal things like "trasnfer done" or "fifo empty".

OK...

> If there's nothing
> on the bus, you don't end up doing any transfers, so you don't get any
> spurious interrupts.

That much is clear even to me, but I'm doing 128 transfers/second
without seeing any spurious interrupts. But I guess my observation
matches the second alternative in one of your earlier messages (where
the first alternative, as far as I understood, was about interrupts
from the i2c device itself...) - i.e. interrupts being dispatched to
multiple cores. This obviously can't happen on the RPi 0/1 that I've
tried, since they're single-core.

--Per

> I can't reproduce this using RTC or EEPROM chips.  We use ADS1013 parts
> at $work, I may have some around here somewhere.  If so, I'll see if I
> can reproduce the problem using them.
> 
> -- Ian
>