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Vinod Koultiwai
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ALSA - hda: Fix timestamping documentation
Some typos in the documentation, so fix them up. Signed-off-by: Vinod Koul <[email protected]> Signed-off-by: Takashi Iwai <[email protected]>
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Documentation/sound/alsa/timestamping.txt

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@@ -14,7 +14,7 @@ provides a refined estimate with a delay.
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event or application query.
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The difference (tstamp - trigger_tstamp) defines the elapsed time.
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The ALSA API provides reports two basic pieces of information, avail
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The ALSA API provides two basic pieces of information, avail
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and delay, which combined with the trigger and current system
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timestamps allow for applications to keep track of the 'fullness' of
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the ring buffer and the amount of queued samples.
@@ -53,21 +53,21 @@ case):
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The analog time is taken at the last stage of the playback, as close
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as possible to the actual transducer
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The link time is taken at the output of the SOC/chipset as the samples
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The link time is taken at the output of the SoC/chipset as the samples
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are pushed on a link. The link time can be directly measured if
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supported in hardware by sample counters or wallclocks (e.g. with
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HDAudio 24MHz or PTP clock for networked solutions) or indirectly
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estimated (e.g. with the frame counter in USB).
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The DMA time is measured using counters - typically the least reliable
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of all measurements due to the bursty natured of DMA transfers.
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of all measurements due to the bursty nature of DMA transfers.
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The app time corresponds to the time tracked by an application after
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writing in the ring buffer.
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The application can query what the hardware supports, define which
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The application can query the hardware capabilities, define which
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audio time it wants reported by selecting the relevant settings in
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audio_tstamp_config fields, get an estimate of the timestamp
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audio_tstamp_config fields, thus get an estimate of the timestamp
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accuracy. It can also request the delay-to-analog be included in the
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measurement. Direct access to the link time is very interesting on
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platforms that provide an embedded DSP; measuring directly the link
@@ -169,7 +169,7 @@ playback: systime: 938107562 nsec, audio time 938112708 nsec, systime delta -51
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Example 1 shows that the timestamp at the DMA level is close to 1ms
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ahead of the actual playback time (as a side time this sort of
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measurement can help define rewind safeguards). Compensating for the
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DMA-link delay in example 2 helps remove the hardware buffering abut
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DMA-link delay in example 2 helps remove the hardware buffering but
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the information is still very jittery, with up to one sample of
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error. In example 3 where the timestamps are measured with the link
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wallclock, the timestamps show a monotonic behavior and a lower

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