Coma FW-C2800 User's Guide download pdf (Page 265)

Types of Devices

7-46

7.17 Types of Devices

There are two main types of devices: terminating devices and stackable

devices. Each exports the same device functions, but they implement them

slightly differently. A terminating device is any device that is a data source or

sink. A stackable device is any device that does not source or sink data, but

uses the DEV functions to send (or receive) data to or from another device.

Refer to Figure 7-12 to see how the stacking and terminating devices fit into

a stream.

Figure 7-12. Stacking and Terminating Devices

Within the broad category of stackable devices, there are two distinct types.

These are referred to as in-place stacking devices and copying stacking

devices. The in-place stacking device performs in-place manipulations on

data in buffers. The copying stacking device moves the data to another buffer

while processing the data. Copying is necessary for devices that produce

more data than they receive (for example, an unpacking device or an audio

decompression driver), or because they require access to the whole buffer to

generate output samples and cannot overwrite their input data (for example,

an FFT driver). These types of stacking devices require different

implementation, since the copying device might have to supply its own

buffers.

Figure 7-13 shows the buffer flow of a typical terminating device. The

interaction with DSP/BIOS is relatively simple. Its main complexities exist in

the code to control and stream data to and from the physical device

Task

SIO

Stackable

Device

Terminating

Device

SIO calls

DEV calls

1 2 ... 260 261 262 263 264 265 266 267 268 269 270 ... 275 276

No comments

Coma FW-C2800 User's Guide Page 265