Communication to the Stream Handler

The SHDEntryPoint contains the following two messages. These messages are located in the SHDD.H file of the \TOOLKIT\H subdirectory. SHDD.H contains the data structures, their type definitions, and #define statements for certain values. Note that the messages pass pointers to packets of data, to allow maximum flexibility for the future.

SHD_REPORT_INT

The PDD uses this message when it needs things at interrupt time. For example, it uses this message to tell the stream handler it has used up all the data and needs some more.

When the stream handler gets the call, it knows the PDD is passing back a buffer that it might already have consumed. So the stream handler returns on that call, giving the PDD a fresh buffer to consume.

SHD_REPORT_EVENT
The stream handler uses this message to keep in sync with what the PDD is doing. For example, the stream handler can request the PDD to report back every tenth of a second that data is played. And the stream handler has all the logic to handle these events. The PDD examines the request, and during its checks when it realizes a tenth of a second has been played in data, the PDD calls SHD_REPORT_EVENT. The stream handler can do what it wants at this point, and the PDD returns.

The PDD is the only one that really knows what is going on. In other words, only the PDD knows how much data, to the millisecond, has been played out to the device. The stream handler can approximate the data played, using calculations based on how much data has gone by. But the stream handler cannot calculate the data played to the millisecond, or even to the fraction of a millisecond, the way the PDD can.

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