1 Jul
2010
1 Jul
'10
11:53 a.m.
On Wed, Jun 30, 2010 at 05:28:05PM +0200, Clemens Ladisch wrote:
The default parameters of this tool are unrealistic; the next MIDI
command is always sent immediately after the previous one has been
received, which tends to align everything to USB frames. Please use
the -w and -r options.
Absolutely. I already suspected 4ms being correlated to USB frames
(granularity 1ms, right?)
With random wait, it looks like this:
latency distribution:
...
3.1 - 3.2 ms: 1 #
...
3.9 - 4.0 ms: 1 #
4.0 - 4.1 ms: 9903 ##################################################
...
5.0 - 5.1 ms: 95 # latency distribution:
...
3.0 - 3.1 ms: 86 ####
3.1 - 3.2 ms: 986 ##################################################
3.2 - 3.3 ms: 958 #################################################
3.3 - 3.4 ms: 967 #################################################
3.4 - 3.5 ms: 985 ##################################################
3.5 - 3.6 ms: 927 ###############################################
3.6 - 3.7 ms: 966 #################################################
3.7 - 3.8 ms: 938 ################################################
3.8 - 3.9 ms: 980 ##################################################
3.9 - 4.0 ms: 904 ##############################################
4.0 - 4.1 ms: 906 ##############################################
4.1 - 4.2 ms: 45 ##
4.2 - 4.3 ms: 44 ##
4.3 - 4.4 ms: 38 ##
4.4 - 4.5 ms: 28 #
4.5 - 4.6 ms: 37 ##
4.6 - 4.7 ms: 34 ##
4.7 - 4.8 ms: 54 ###
4.8 - 4.9 ms: 34 ##
4.9 - 5.0 ms: 42 ##
5.0 - 5.1 ms: 40 ##
...
5.2 - 5.3 ms: 1 #
Probably still acceptable, given that the majority of packets deviates
by only 1ms.
Does USB have a notion of "ticks" (clock?), that is, frames are sent at
isochronous distances? Or is the host controller free to send a packet
whenever it wants to? Without the latter, 1ms jitter could be the result
of queueing up the data for the next time slot.
TIA
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