RE: [PATCH v3 1/4] Add correlated clocksource deriving system time from an auxiliary clocksource

-----Original Message-----
From: Peter Zijlstra [mailto:peterz@infradead.org]
Sent: Friday, September 04, 2015 7:28 AM
To: Richard Cochran
Cc: Hall, Christopher S; Thomas Gleixner; Kirsher, Jeffrey T;
hpa@zytor.com; mingo@redhat.com; john.stultz@linaro.org; x86@kernel.org;
linux-kernel@vger.kernel.org; netdev@vger.kernel.org; intel-wired-
lan@lists.osuosl.org
Subject: Re: [PATCH v3 1/4] Add correlated clocksource deriving system time
from an auxiliary clocksource

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(several milliseconds) and the result will be out of date by some

fraction of that

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amount.

Why does it take milliseconds to read one audio time stamp?

So what I suspect, but please correct me if I'm wrong Chris, is that a
DSP will buffer and process audio signals, and only later wake up the
main CPU.

So by the time the CPU is made aware of the data, it's 'old'.

That's about right.  The DSP runs on a 1 ms cadence.  Any access to registers controlled by the DSP will take 1-2 DSP ticks to access.