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authorVinod Koul <vinod.koul@intel.com>2016-07-11 06:13:29 -0400
committerTakashi Iwai <tiwai@suse.de>2016-07-11 06:45:39 -0400
commita5d48be457273e4faf34a2033c63f8890f3f9c6c (patch)
treed46f9c675d80c3306d86a7c919f3808794a23c36 /Documentation/sound/alsa
parent860c1994a70a0d2ab6f87fb7e72e722a8fb2c64c (diff)
ALSA - hda: Fix timestamping documentation
Some typos in the documentation, so fix them up. Signed-off-by: Vinod Koul <vinod.koul@intel.com> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/sound/alsa')
-rw-r--r--Documentation/sound/alsa/timestamping.txt12
1 files changed, 6 insertions, 6 deletions
diff --git a/Documentation/sound/alsa/timestamping.txt b/Documentation/sound/alsa/timestamping.txt
index 1b6473f393a8..9d579aefbffd 100644
--- a/Documentation/sound/alsa/timestamping.txt
+++ b/Documentation/sound/alsa/timestamping.txt
@@ -14,7 +14,7 @@ provides a refined estimate with a delay.
14event or application query. 14event or application query.
15The difference (tstamp - trigger_tstamp) defines the elapsed time. 15The difference (tstamp - trigger_tstamp) defines the elapsed time.
16 16
17The ALSA API provides reports two basic pieces of information, avail 17The ALSA API provides two basic pieces of information, avail
18and delay, which combined with the trigger and current system 18and delay, which combined with the trigger and current system
19timestamps allow for applications to keep track of the 'fullness' of 19timestamps allow for applications to keep track of the 'fullness' of
20the ring buffer and the amount of queued samples. 20the ring buffer and the amount of queued samples.
@@ -53,21 +53,21 @@ case):
53The analog time is taken at the last stage of the playback, as close 53The analog time is taken at the last stage of the playback, as close
54as possible to the actual transducer 54as possible to the actual transducer
55 55
56The link time is taken at the output of the SOC/chipset as the samples 56The link time is taken at the output of the SoC/chipset as the samples
57are pushed on a link. The link time can be directly measured if 57are pushed on a link. The link time can be directly measured if
58supported in hardware by sample counters or wallclocks (e.g. with 58supported in hardware by sample counters or wallclocks (e.g. with
59HDAudio 24MHz or PTP clock for networked solutions) or indirectly 59HDAudio 24MHz or PTP clock for networked solutions) or indirectly
60estimated (e.g. with the frame counter in USB). 60estimated (e.g. with the frame counter in USB).
61 61
62The DMA time is measured using counters - typically the least reliable 62The DMA time is measured using counters - typically the least reliable
63of all measurements due to the bursty natured of DMA transfers. 63of all measurements due to the bursty nature of DMA transfers.
64 64
65The app time corresponds to the time tracked by an application after 65The app time corresponds to the time tracked by an application after
66writing in the ring buffer. 66writing in the ring buffer.
67 67
68The application can query what the hardware supports, define which 68The application can query the hardware capabilities, define which
69audio time it wants reported by selecting the relevant settings in 69audio time it wants reported by selecting the relevant settings in
70audio_tstamp_config fields, get an estimate of the timestamp 70audio_tstamp_config fields, thus get an estimate of the timestamp
71accuracy. It can also request the delay-to-analog be included in the 71accuracy. It can also request the delay-to-analog be included in the
72measurement. Direct access to the link time is very interesting on 72measurement. Direct access to the link time is very interesting on
73platforms that provide an embedded DSP; measuring directly the link 73platforms that provide an embedded DSP; measuring directly the link
@@ -169,7 +169,7 @@ playback: systime: 938107562 nsec, audio time 938112708 nsec, systime delta -51
169Example 1 shows that the timestamp at the DMA level is close to 1ms 169Example 1 shows that the timestamp at the DMA level is close to 1ms
170ahead of the actual playback time (as a side time this sort of 170ahead of the actual playback time (as a side time this sort of
171measurement can help define rewind safeguards). Compensating for the 171measurement can help define rewind safeguards). Compensating for the
172DMA-link delay in example 2 helps remove the hardware buffering abut 172DMA-link delay in example 2 helps remove the hardware buffering but
173the information is still very jittery, with up to one sample of 173the information is still very jittery, with up to one sample of
174error. In example 3 where the timestamps are measured with the link 174error. In example 3 where the timestamps are measured with the link
175wallclock, the timestamps show a monotonic behavior and a lower 175wallclock, the timestamps show a monotonic behavior and a lower