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Intel High Definition Audio: Difference between revisions
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comment on many vendor defined widgets
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With all these buffers, the DMA engines jump back to the start and carry on running from there infinitely until you stop them, although with CORB there is a register which stores the last valid command which the DMA engine must stop at (after sending that command) and it will only move on again when that register is modified (by you) to enable more commands to be sent. It is the job of your software to collect data from input buffers before they are overwritten on the next lap. The set of data buffers defined by descriptors for a single stream collectively comprise a cyclic stream buffer, but it's divided up into chunks defined by descriptors to enable an interrupt to be generated at the end of each chunk (interrupt optional) so that you can write new data into an output buffer that's just been sent before the DMA engine returns to that buffer on the next lap, or to copy data out of an input buffer that's just been written by a DMA engine to make way for more data to be written on the next lap.
At the codec end, you will need to start out by interrogating the root node of each of 15 possible codecs. The STATESTS register at offset 0Eh indicates which codec addresses have codecs at the end of them. The verb F00h will then be used with an 8-bit parameter to request information such as vendor ID, device ID and the starting node number and number of nodes for the function groups in the codec. Having found the function groups, you can use the same verb to interrogate them to find out the starting node number and number of nodes of their widgets, and also the type of the function group itself - AFG (audio function group) is the one you probably want unless you're looking for a modem. You can then interrogate each widget to ask it what its type is (e.g. output, input, mixer, selector, pin complex, power widget, volume knob). Another verb, F02h, allows you to get a connection list of other widgets in the same function group directly connected to the widget you're interrogating, though you need to use verb F00h first and the parameter at 0Eh to get the connection list length. On the Netbook I program on there is only one codec, one function group (AFG) and 37 widgets (about half of which are vendor defined audio widgets, though many of those don't even exist on the codec manufacturer's datasheet). Don't expect there to be a volume control widget: the volume can be controlled by setting different amplifier levels at the input and output controllers instead.
== Device Registers ==
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