5 functional timing, Section 7.5, “functional timing – Intel PXA26X User Manual
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Intel® PXA26x Processor Family Developer’s Manual
7-15
Liquid Crystal Display Controller
If dummy pixels are to be inserted, the panel must ignore the extra pixel clocks at the end of each
line that correspond to the dummy pixels.
Use the following equation to calculate the total size of the frame buffer (in bytes). This calculation
encodes the length of the frame buffer in the DMA descriptors (
Section 7.6.5.5.4, “Transfer Length
(LEN)” on page 7-41
). The first term is the size required for the encoded pixel values. Lines is the
number of lines for the display. Pixels is the number of pixels per line. Use the actual line/pixel
count, not minus 1 as in the LCCR registers. n = the number of extra dummy pixels required per
line (as described above). For dual-panel mode, the frame-buffer size is equally distributed
between the two DMA channels. Therefore, lines in this equation are divided in half for dual-panel
mode
.
The bandwidth required for the LCD controller can be calculated using the following equations.
FrameBufferSize is the result of the previous equation. Bandwidth is always an important part of
any system analysis. Systems with large panels and high number of bits per pixel must ensure that
the panel is not starved for data.
.
Sample calculations for a 640x480 panel, 16-bits per pixel, 60 Hz refresh rate:
FrameBufferSize = 16*640*480/8 = 614,400 bytes
Bus Bandwidth = 614,400 * 60 = 36.9 MB/sec
The amount of available bus bandwidth is heavily dependant on the PXBus frequency. Systems
using large panels must ensure that the PXBus frequency, controlled by the run mode frequency, is
configured as high as possible.
7.5
Functional Timing
through
illustrate LCD controller timing in passive display mode. The
example used is a 320x240 panel.
and
illustrate the LCD controller timing
in active display mode. For precise timing relationships, see the Intel® PXA26x Processor Family
Electrical, Mechanical, and Thermal Specification.
FrameBufferSize
BitsPerPixel
Lines
Pixels
n
+
(
)
•
•
8
--------------------------------------------------------------------------
=
BusBandwidth
FrameBufferSize
PaletteSize
+
(
)
RefreshRate
•
=
BusBandwidth DualPanel
(
)
FrameBufferSize
2
•
PaletteSize
+
(
)
RefreshRate
•
=