Date: Tue, 20 Aug 2019 13:50:08 +0200 From: Hans Petter Selasky <hps@selasky.org> To: Per Hedeland <per@hedeland.org>, Ian Lepore <ian@freebsd.org> Cc: freebsd-arm@freebsd.org Subject: Re: Is it a good idea to use a usb-serial adapter for PPS? Yes, it is. Message-ID: <ce77ae35-40dc-1f97-110f-74e354cf3725@selasky.org> In-Reply-To: <8e28c96e-92c6-5beb-277f-0876a5aba272@hedeland.org> References: <alpine.BSF.2.21.99999.352.1908071046410.98975@autopsy.pc.athabascau.ca> <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> <345bae77417c2495f55799b4c7ca2784f4ece9ed.camel@freebsd.org> <7312032d-2908-9414-0445-6b442c3a02e5@hedeland.org> <523b6f0a0fa5f2aeec298fa74df25d3c4af66acc.camel@freebsd.org> <0426fc8b-5398-d8ab-561e-7823c24403a5@hedeland.org> <24b0eaf25b64d6098b390df092866c69e352d859.camel@freebsd.org> <16c91be1-6f2a-b26d-22c7-be8e4ba8eec0@hedeland.org> <72a964c78cbfc36be2345919633ca2196f0783e3.camel@freebsd.org> <fe2c2d77-3030-6734-e1d8-c1375f231a24@hedeland.org> <cd1b38bb0b8873af96a41bce1b03676f735ae3f9.camel@freebsd.org> <540c8b5f-5e81-b67b-4a00-49b86044efe0@selasky.org> <8e28c96e-92c6-5beb-277f-0876a5aba272@hedeland.org>
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On 2019-08-20 13:38, Per Hedeland wrote: > > I'm sorry, I'm afraid I still don't really understand... The question, > at least in my mind, was whether polling was done in a "strictly > periodic" fashion, at most once per 125 us for USB 2.0 - or whether > the host controller would poll "as fast as it could", which could > result in a *much* higher polling rate. That depends on the endpoint type. INTERRUPT endpoints poll regularly, one time, every 125 us for example, when a job is queued. BULK endpoints poll all the time, depending a bit on the HC in use. Anyways, the computer is not notified of the completion before the HC is generating an interrupt. This usually happens at some fixed point in time. I.E. multiple completions can be joined into one HC interrupt. It is the completion interrupt which notifies the software about the PPS event. --HPS
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