Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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Multichannel Operation
11-64 ADSP-BF535 Blackfin Processor Hardware Reference
Window Size
The window size defines the range of the channels that can be enabled/dis-
abled in the current configuration. It can be any value in the range of 8 to
128, in increments of 8; the default value of 0 corresponds to a minimum
window size of 8 channels. Since the DMA buffer size is always fixed, it is
possible to define a smaller window size (for example, 32 bits), resulting in
a smaller DMA buffer size (in this example, 32 bits instead of 128 bits) to
save DMA bandwidth. The window size cannot be changed while the
SPORT is enabled.
Window Offset
The window offset specifies where in the 127-channel range to place the
start of the window. A value of 0 specifies no offset and permits using all
128 channels. As an example, a program could define a window with a
window size of 5 and an offset of 93. This 5-channel window would reside
in the range from 93 to 97. The window offset cannot be changed while
the SPORT is enabled.
If the combination of the window size and the window offset would place
the window outside of the range of the channel enable registers, none of
the channels in the frame are enabled, since this combination is invalid.
Other Multichannel Fields in SPORTx_TX_CONFIG,
SPORTx_RX_CONFIG
A multichannel frame contains more than one channel, as specified by the
window size and window offset; the multichannel frame is a combined
sequence of the window offset and the channels contained in the window.
The total number of channels in the frame is calculated by adding the
window size to the window offset.