Datasheet

6
AVR32416
Figure 2. 2D Frame Buffer Addressing
2.3 Bandwidth considerations
An attached display needs a lot of bandwidth from the expansion bus of the system.
This must be considered in the display selection process. The bandwidth needed is
calculated by following formula:
NeededBandwidth = DispaySize x BitsPerPixel x FrameRate
Depending on the applications an operating system is running in parallel enough
bandwidth should be available. For instance considering that the updating of the
frame buffer could be at the same frame rate as the display the above formula must
be multiplied by two. To calculate the available bandwidth on the system following
formula can be used:
AvailableBandwidth = BusSpeed x BusInterfaceWidth
The maximum available bandwidth for the AP700x devices is
AvailableBandwidth = 75 x 32/8 MB/s = 300 MB/s
due to the maximum bus speed of 75 MHz. With the maximum speed it is possible to
use displays up to VGA with full 24bit resolution and doing MPEG4 decoding at the
same time. Larger displays can be used when the resolution is decreased.
2.3.1 32-bit memory example (as on the STK1000)
For the display on the STK
®
1000 (DisplaySize 320x240, BitsPerPixel 24, FrameRate
75Hz) the formula delivers following result.
NeededBandwidth = 320 x 240 x 24/8 x 75 Byte/s = 17MByte/s
For the AP700x device the maximum bus frequency is 75MHz and the interface width
to the memory on the STK1000 is 32bit wide. This results in the following maximum
available bandwidth:
AvailableBandwidth = 75 x 32/8 MB/s = 300 MB/s
A VGA display would need approximately
NeededBandwidth = 640 x 480 x 24/8 x 75 Bytes/s = 69 MByte/s
assuming the same frame rate.
32105-AVR32-07/08