PPI Registers
7-28
ADSP-BF537 Blackfin Processor Hardware Reference
When the
SKIP_EN
bit is set, the
SKIP_EO
bit allows the PPI to ignore
either the odd or the even elements in an input datastream. This is useful,
for instance, when reading in a color video signal in YCbCr format (Cb,
Y, Cr, Y, Cb, Y, Cr, Y...). Skipping every other element allows the PPI to
only read in the luma (Y) or chroma (Cr or Cb) values. This could also be
useful when synchronizing two processors to the same incoming video
stream. One processor could handle luma processing and the other (whose
SKIP_EO
bit is set differently from the first processor’s) could handle
chroma processing. This skipping feature is valid in ITU-R 656 modes
and RX modes with external frame syncs.
The
PACK_EN
bit only has meaning when the PPI port width (selected by
DLEN[2:0]
) is 8 bits. Every
PPI_CLK
-initiated event on the DMA bus (that
is, an input or output operation) handles 16-bit entities. In other words,
an input port width of 10 bits still results in a 16-bit input word for every
PPI_CLK
; the upper 6 bits are 0s. Likewise, a port width of 8 bits also
results in a 16-bit input word, with the upper 8 bits all 0s. In the case of
8-bit data, it is usually more efficient to pack this information so that
there are two bytes of data for every 16-bit word. This is the function of
the
PACK_EN
bit. When set, it enables packing for all RX modes.
Consider this data transported into the PPI via DMA:
0xCE, 0xFA, 0xFE, 0xCA....
• With
PACK_EN
set:
This is read into the PPI, configured for an 8-bit port width:
0xCE, 0xFA, 0xFE, 0xCA...
This is transferred onto the DMA bus:
0xFACE, 0xCAFE, ...
Содержание Blackfin ADSP-BF537
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Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...