Texas Instruments TMS320 User Manual page 267

Opening Devices
The configurable device parameters are used to set the operating parameters
of the hardware. There are no DSP/BIOS constraints on which parameters
should be set in Dxx_init rather than in Dxx_open.
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The object semaphore objptr sync is typically used to signal a task that is
pending on the completion of an I/O operation. For example, a task can call
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SIO_put, which can block by pending on objptr sync. When the required
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output is accomplished, SEM_post is called with objpt sync. This makes a
task blocked in Dxx_output ready to run.
DSP/BIOS does not impose any special constraints on the use of
synchronization semaphores within a device driver. The appropriate use of
such semaphores depends on the nature of the driver requirements and the
underlying hardware.
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The ready semaphore, objptr ready, is used by Dxx_ready, which is called
by SIO_select to determine if a device is available for I/O. This semaphore is
explained in section 4.7, Semaphores, page 4-59.
Streaming I/O and Device Drivers 7-37