Intel® 82801AA (ICH) & Intel® 82801AB (ICH0) I/O Controller Hub AC ’97 Programmer’s Reference Manual wrote:The Buffer Descriptor list is an array of up to 32 entries, each of which describes a data buffer. Each entry contains a pointer to a data buffer, control bits, and the length of the buffer being pointed to, where the length is expressed as the number of samples. This, combined with the 16-bit sample size, gives the actual physical length of the buffer. The buffer length is restricted to 65536 samples. “0” in the buffer length indicates no samples to process. Each descriptor can point to a buffer of a different size. The samples are stored two per DWord (16-bit samples). In the case of audio PCM, these represent the left and right channels, respectively.

Intel® I/O Controller Hub 6 (ICH6) High Definition Audio / AC ’97 Programmer’s Reference Manual (PRM) May 2005. wrote:4.6.3 Starting Streams
To create a stream, the software must first determine the appropriate stream parameters, such as
sample rate, bit depth, and number of channels. The controller and codec resources should be
checked to make sure sufficient resources are available to support the desired stream format.

A data buffer and BDL buffer are then allocated from the proper memory pool, making sure that
the proper buffer alignment and caching requirements are met. The BDL is constructed to describe
the stream data buffer, including setting Interrupt on Completion bits at the points interrupts are
desired. Software then allocates a Stream Descriptor (Input or Output, as appropriate), and
configures the Descriptor with the stream format, BDL address, Cyclic Buffer Length, interrupt
policy, and other necessary register settings.

The codec is next configured by configuring the appropriate Audio Input or Output Converters
with the stream ID and format information. Other widgets in the audio path are configured so that
the audio data flows to (or from) the Pin Complex Widgets, with Connection Select, Amplifiers,
Processing Controls, and all other controls in the audio path set as appropriate. At this point, the
codec is ready to accept data if the stream is an output stream or begins sending data on the link for
an input stream.

The Stream Descriptor’s RUN bit is then set to 1 to start the DMA engine and begin the transfer of
data to or from the link.

IDT unknown codec id 00007608