MB87P2020 Datasheet, PDF (205/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

Graphic Processing Unit
interrupt case the GPU ceases data fetching for the remaining frame period and triggers the ULB flag
BWVIO (bit 18 of ULB flag word). However, display output continues with blank pixel data to pre-
vent possible damage at the connected display. This state is left either by soft-reset (i.e. switching
MasterTimingOn off and back on again) or at the begin of the next frame period. If bandwidth is
still too small the interrupt will be raised again.
• The priority with which GPU requests data from SDC can be controlled with the settings in the
GPU_SDCPrio register (bits [6:4] and [2:0]¹, address 0x3270). Per default the GPU has the highest
priority amongst all GDC units. Any changes of this value should be done with utmost care, since a
continuous display timing requires a continuous data stream from RAM be maintained.
6.3 Image Processing
There are some points to be aware of when processing image data in YUV color space:
• Matrix coefficients CBxG and CRxG are treated as having negative sign
• YUV555 and YUV655 color spaces are auto scaled to YUV444 before matrix multiplication
• Processing YUV422 data restricts horizontal first pixel, window size and offset to even values
• There is only either a mapping through matrix or achromatic mapping from YUV color spaces to
intermediate and eventually to physical color space. Therefore, if a direct mapping from YUV to
GPU pins is desired a special approach is necessary. It consists of a re-labelling of layers containing
YUV data to corresponding RGB color spaces with an equal number of bits per pixel (table 6-1) and
then directly mapping these to the physical color space and thus to the pins (cf. table 3-14). Note also
that YUV422 uses chrominance multiplexing.
Table 6-1: Compatibility list for YUV to RGB re-labelling.
YUV spaces
Corresponding
RGB spaces
YUV422
RGB565
YUV444
RGB888
YUV555
RGB555
YUV655
RGB565
• Image quality for pictures in YUV422 may be improved by using chrominance interpolation.
• To improve image appearance for video pictures grabbed by VIC, GPU offers line doubling. With
this feature (which can be switched on individually for each layer) vertical resolution is reduced to
the half by displaying each line in VideoRAM twice on the display (e.g. line #0 from RAM is dis-
played on display lines #0 and #1, RAM line #1 on display lines #2 and #3 and so on). This approach
eliminates inter-field jitter. When used in conjunction with field dropping in VIC it additionally
reduces memory bandwidth.
• Pixels of layers in color space RGB555, RGB565 and RGB888 may be fed through the gamma tables
to apply further color processing. This mode is enabled when both flags, gamma enable and RGB
gamma forcing, are set. Similar arbitrary color processing is achieved for color spaces with less than
16 bits per pixel by simply using the CLUT.
1. Bits [2:0] for low priority are not used in the current implementation, i.e. GPU always uses high priority
requests.
Functional Peculiarities
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