MB87P2020 Datasheet, PDF (198/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

MB87J2120, MB87P2020-A Hardware Manual
5 Bandwidth Considerations
5.1 Processing Bandwidth
5.1.1 Average Bandwidth
For a first go/no go decision an estimation of average GPU bandwidth demands might be sufficient. It is
done on the basis of the number of pixels processed per frame and the frame period. In general, the condition
T _proc ≤ T _frame
(12)
must hold for the GPU to work properly. These two periods are calculated as follows:
a) Frame period:
T _frame = T _DisplayClock ⋅ ∆x ⋅ ∆y
(13)
∆x = XStop – XStart
(14)
∆y
=





YoddStop – YoddStart + 1
12-- _{⋅ ((YoddStop – YoddStart + 1) + (YevenStop – YevenStart + 1))}
for disabled field-toggling
for enabled field-toggling
(15)
b) Processing period:
T _proc= T _background + T _layers
= T _CoreClock ⋅ (DisplayArea + LayerArea)
∑ ^{= T} CoreClock ^⋠_{(}^{PhysX ⋅ PhysY) +} _{visible layers} ^(WXi ^{⋅ WY}i^{)}
(16)
Note 1: DisplayArea counts only when background is enabled.
Note 2: LayerArea counts only for potentially visible pixels, i.e. parts of layers outside the physical display
area need not be processed and therefore do not count here. However, pixels hidden underneath others do
count.
5.1.2 Peak Bandwidth
To have a more reliable statement about whether or not confirming to bandwidth restrictions the peak band-
width has to be calculated, since this is virtually the limiting constraint. Therefore, a more detailed elabo-
ration into GPU function is necessary.
Pixels are processed in portions of one line segment. The size of one such line segment is a function of the
visible layers logical color spaces, the physical color space, an internal burst limit (512 pixels) for Video-
RAM accesses, and the actual number of pixels per line.
SegLen= min(32 ⋅ min(ppw_{log, l}), 32 ⋅ ppw_phys, 512, PhysSizeX)
(17)
The values for the number of pixels per word (either per VideoRAM word or per LSA word) according to
color spaces are given in tables 5-1 and 5-2. In the special case that no layer is active min(ppw_{log, l}) defaults
to 1.
2. Due to internal FIFOs the physical display is affected with a delay dependent on picture size, visible layers
and their color resolution.
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