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Sat, 20 Apr 2019 12:39:35 +0200 (CEST) (envelope-from per@hedeland.org) Subject: Re: I2c producing crazy console messages [[Re: insanely-high interrupt rates -- PARTIAL resolution (Pi2)]] To: Ian Lepore Cc: Karl Denninger , freebsd-arm@freebsd.org References: <004ddba628b94b80845d8e509ddcb648d21fd6c9.camel@freebsd.org> <669892ac3fc37b0843a156c0ab102316829103fd.camel@freebsd.org> <663f2566-b035-7011-70eb-4163b41e6e55@denninger.net> <20190325164827.GL57400@cicely7.cicely.de> <3db9cf8a-68ee-e339-67bf-760ee51464fd@denninger.net> <874l7fyrpr.fsf@news-spur.riddles.org.uk> <701e011f-3088-8ed4-4fbb-6fa93ac698f5@denninger.net> <67133e19-2be5-ccd1-2ded-008b36a866ec@denninger.net> <6f6f8471-8624-c5e2-547c-42b712254126@denninger.net> <8bcdb1e1-e561-6255-848d-e532ad4d5918@denninger.net> <499b53d5-23ed-c33b-3715-018720c536a3@hedeland.org> From: Per Hedeland Message-ID: Date: Sat, 20 Apr 2019 12:39:34 +0200 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 20 Apr 2019 10:39:44 -0000 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 >