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IO Cycle Telemetry, USB Audio and AC-3 questions

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IO Cycle Telemetry, USB Audio and AC-3 questions

Subject: IO Cycle Telemetry, USB Audio and AC-3 questions
From: Fabian Renn <email@hidden>
Date: Mon, 8 Aug 2005 17:10:23 +0200

Hi again,

I may sound repetitive, but again: i'm working on a driver for a usb audio device. My driver works fine when i work with buffer sizes around 6144 samples. Yet AC-3 needs a buffer size of 1536 samples, and thats where the problems begin. When working with 1536 samples i keep on getting clicks in my sound. Now I'm checking with the IO Cycle Telemetry but i'm not quite sure what the values mean. With a buffer of 1536 samples i get values in the Zero:samp column about every 4th row. The whole row is black. Every now and then i get red rows: Looking at the detailed view of the red row i get a red row that starts with '0 Early'. What does this mean ( copy below )? The problem with usb audio, is that the HAL can only get an update about the buffer locations every 1 ms and the time stamp resolution is at most 1 ms ( because a usb frame takes 1 ms to process ). I'm already trying to smooth this out as much as possible: first of all, i try to smooth out my outgoing frames as much as possible, so that there are not too many variations of how many bytes are transfered with each isoc frame; i take a time stamp of the frTimeStamp value for every frame that will cause a wrap. Furthermore I add/remove a couple of nanos to this value according to how many bytes the frReqCount value is away from 48 samples ( at 48 kHz sample rate ) ( because the time stamp of frTimeStamp was taken after the whole frame completed. Yet if only, for example 24 samples, were transfered, the wrap would have happened a half a ms earlier ). My driver logs the time stamps and i'm getting a variation of about 1 ms ( the difference between two time stamps is always around 32-33 ms, ideally i should be getting exactly 32 ms ( 1536 / 48 ) ). Is this variation too much? My guess is that the clicking is coming from the getCurrentSampleFrame method. At first i would always return a calculated buffer location, that i calculated from validating the frame lists when each frame completes. I do this validation every time i get a usb completion, and every time clipOutputSamples is called ( exactly like in AppleUSBAudio ), but no more than that. This resulted in immense clicking at a buffer size of 1536. Now, when getCurrentSampleFrame gets called, i get the current usb frame from the usb controller and take the difference from the usb frame when my sample buffer pointer ( the one that gets calculated in my frame list validation routine ) was last updated. With this difference i calculate a minor offset to the sample buffer pointer. This reduced the clicking a lot, but didn't eliminate it totally. Does anyone have some tips?

Greetings

Fabian

Black Rows: Start Offset Late Rate Now:samp Now:host In:samp In:host Out:samp Out:host Wake:samp Wake:host Zero:samp Zero:host 31.949 10.657 0.035 1.000072 778807 31.949 778147 18.185 779465 45.645 778825 32.312 778752 30.781 42.612 10.663 0.029 1.000072 779319 42.612 778659 28.852 779977 56.313 779337 42.987 53.283 10.671 0.033 1.000072 779831 53.283 779171 39.520 780489 66.980 779848 53.634 63.952 10.669 0.035 0.999940 780343 63.952 779683 50.176 781001 77.633 780364 64.368 780288 62.786 74.625 10.673 0.055 0.999940 780856 74.625 780195 60.842 781513 88.299 780885 75.236 85.273 10.647 0.036 0.999940 781367 85.273 780707 71.508 782025 98.965 781384 85.624 95.946 10.673 0.043 1.000045 781880 95.946 781219 82.183 782537 109.642 781900 96.376 781824 94.784 106.615 10.669 0.035 1.000045 782391 106.615 781731 92.850 783049 120.310 782411 107.028 117.283 10.668 0.035 1.000045 782903 117.283 782243 103.517 783561 130.977 782922 117.678 127.949 10.666 0.034 0.999980 783415 127.949 782755 114.179 784073 141.637 783433 128.305 783360 126.784

Red Row: 191.940 10.661 0.031 1.000000 786487 191.940 785877 178.226 787195 205.684 786552 192.289 786432 189.788 0 Early: 1467 .... _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden Follow-Ups: Re: IO Cycle Telemetry, USB Audio and AC-3 questions From: Jeff Moore <email@hidden> Prev by Date: How to save/load custom audio driver properties Next by Date: Filter Cookbook...again Previous by thread: Re: How to save/load custom audio driver properties Next by thread: Re: IO Cycle Telemetry, USB Audio and AC-3 questions Index(es): Date Thread