Re: audio callback intervals
Re: audio callback intervals
- Subject: Re: audio callback intervals
- From: Matthew Xavier Mora <email@hidden>
- Date: Wed, 6 Mar 2002 09:12:23 -0800
At 11:27 PM -0800 3/5/02, Kurt Bigler wrote:
Also, I am aware that isochronous transfers on a Firewire bus occur in
bursts that are not evenly spaced but have the correct average rate. So
conceivably a driver for audio over firewire might want to present the data
as it becomes available which might not be at equal intervals, and leave it
up to the application to do the best thing with this for its own purposes.
This is not entirely true. Audio data can be presented in two modes.
Blocking and non-blocking.
In the blocking case, the driver waits until there is enough samples
to fill a packet before sending it on the wire. It will send empty
packets in the mean time until enough samples have come in.
In non-blocking mode the driver sends whatever has arrived, every 125uS.
In either case this is way below what the application will see.
Because of how the HAL operates, your application should always get
callback evenly spaced and the driver will deal with the
packetization of audio samples.
Matt
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