TVP4020
Programmers Reference Manual
Programming Tips
145
or a WaitForCompletion command which does not require the polling of
the output FIFO.
Similarly, if the Framebuffer Write unit is used to clear the localbuffer, or
the Texture Read unit is used in a copy operation, the chip must be
synchronized. The chip will synchronize between localbuffer read and
localbuffer write, and between framebuffer read and framebuffer write.
Any operations that mix buffers need synchronization.
If a texture is downloaded as a normal image, it can make use of the
formatting in the chip to change color format and reorganize the data
into rectangular patches. If texture is already in the required format, a
fast texture download can be used. To use this, set the
TextureDownloadOffset register to point to the start address of the
texture (in 32 bit words). Write 32 bit texture data to the TextureData
register and this will be written to memory without changing format. The
TextureDownloadOffset will automatically increment following each write.
If the texture is 8 bits per texel, then 4 texels must be supplied at a time.
This method of texture download avoids the need to set-up the
Rasterizer for image download and allows the state of the chip to be left
unchanged. Even the framebuffer writes do not have to be enabled.
7.5
Multi Buffering
7.5.1
Fast Double Buffering
P
ERMEDIA
board designs can readily support a variety of double buffering
mechanisms depending on the memory configuration and LUT-DAC
used, including:
•
BLT
•
Full Screen
•
Bitplane
For further details see section §4.4, §5.12.6, §5.12.7 and §5.13 of this
manual.
Note that optimal functionality may be achieved by mixing two or more of
the above double buffering techniques.
As a general performance note, it is best to send non-framebuffer
related commands to P
ERMEDIA
following a SuspendUntilFrameBlank
command. This allows better overlap between the host and P
ERMEDIA
. In
general any commands that will not cause rendering to the framebuffer
to occur can be queued in the P
ERMEDIA
FIFO before waiting on
VBLANK.
Содержание TVP4020 PERMEDIA 2
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