Coma FW-C2800 User's Guide download pdf (Page 235)

Stackable Devices

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7.4 Stackable Devices

The capabilities of the SIO module play an important role in fostering device-

independence within DSP/BIOS in that logical devices insulate your

application programs from the details of designating a particular device. For

example, /dac is a logical device name that does not imply any particular DAC

hardware. The device-naming convention adds another dimension to device-

independent I/O that is unique to DSP/BIOS—the ability to use a single name

to denote a stack of devices.

Note:

By stacking certain data streaming or message passing devices atop one

another, you can create virtual I/O devices that further insulate your

applications from the underlying system hardware.

Consider, as an example, a program implementing an algorithm that inputs

and outputs a stream of fixed-point data using a pair of A/D-D/A converters.

However, the A/D-D/A device can take only the 14 most significant bits of

data, and the other two bits have to be 0 if you want to scale up the input data.

Instead of cluttering the program with excess code for data conversion and

buffering to satisfy the algorithm’s needs, we can open a pair of virtual

devices that implicitly perform a series of transformations on the data

produced and consumed by the underlying real devices as shown in

Example 7-8.

Example 7-8. Opening a Pair of Virtual Devices

SIO_Handle input;

SIO_Handle output;

Ptr buf;

Int n;

buf = MEM_alloc(0, MAXSIZE, 0);

input = SIO_create("/scale2/a2d", SIO_INPUT, MAXSIZE, NULL);

output = SIO_create("/mask2/d2a", SIO_OUTPUT, MAXSIZE, NULL);

while (n = SIO_get(input, &buf)) {

`apply algorithm to contents of buf`

SIO_put(output, &buf, n);

}

SIO_delete(input);

SIO_delete(output);

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Coma FW-C2800 User's Guide Page 235