Intel PXA255 manual Functional Timing, FrameBufferSize =

Models: PXA255

1 600
Download 600 pages 33.14 Kb
Page 278
Image 278

LCD Controller

Use the following equation to calculate the total size of the frame buffer (in bytes). This calculation is used to encode the length of the frame buffer in the DMA descriptors (Section 7.6.5.4). 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.

BitsPerPixel Lines • ( Pixels + n)

FrameBufferSize = -------------------------------------------------------------------------

8

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 bits per pixel must ensure that the panel is not starved for data.

BusBandwidth = (FrameBufferSize + PaletteSize) • RefreshRate

BusBandwidth(DualPanel) = (FrameBufferSize • 2 + PaletteSize) • RefreshRate

Sample calculations for an 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

7.5Functional Timing

Figure 7-12through Figure 7-14illustrate LCD controller timing in passive display mode. The example used is a 320x240 panel. Figure 7-15and Figure 7-16illustrate the LCD controller timing in active display mode.For precise timing relationships, see the Intel® PXA255 Processor Electrical, Mechanical, and Thermal Specification.

7-14

Intel® PXA255 Processor Developer’s Manual

Page 278
Image 278
Intel PXA255 manual Functional Timing, FrameBufferSize =