Re: driver strangeness
Re: driver strangeness
- Subject: Re: driver strangeness
- From: Jeff Moore <email@hidden>
- Date: Thu, 9 Mar 2006 15:22:33 -0800
Did you look at the time stamps the driver produced with HALLab (they
are shown in the last column of the telemetry)? The reason I mention
this is that it is these time stamps that keep the HAL on track so as
to be able to read the correct data from the ring buffer for any
given cycle and not violate the safety offset.
Another thing to look at is the quality of the first time stamp the
driver lays down. This time stamp needs to be the most accurate you
can make it as the HAL uses it as the anchor point for IO. If it is
offset one way or the other, all the HAL's subsequent reads will be
offset by the same amount. This can lead the HAL to violate the
safety offset. For just this reason, it is a good idea for some
drivers to just eat the first time stamp and only show the HAL the
time stamps starting with the second one.
On Mar 9, 2006, at 1:36 PM, david tay wrote:
Jeff,
I've used HALLab and it thinks that everything is just fine - no
late/ early frames.
The data points I currently have indicate that memory size and
speed affect the input stream (for USB 2.0). However, I think those
are just red herrings.
What things could be different between USB 1.1 and 2.0 (other than
higher speed, microframes) ?
David
Sounds like this is most likely a time stamp issue. It's hard to say
without more data.
At any rate, you can use HALLab to look at what the HAL thinks is
going on and how it is interpreting your time stamps.
--
Jeff Moore
Core Audio
Apple
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