Xilinx LogiCORE IP, User Manual

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44 www.xilinx.com Video Scaler v4.0 User Guide
UG805 March 1, 2011
Chapter 8: Coefficients
case, for a 12H-tap x 12V-tap 64-phase filter, you need to write 6 times per phase. If the
user has specified separate H and V coefficients, this is a total of
768 write operations
per set.
• For YC4:2:2 or YC4:2:0 , when not sharing coefficients across H and V operations or
across Y and C operations, one bank of luma (Y) and chroma (C) coefficients must be
loaded into the FIFO
for each dimension before they can be streamed into the
coefficient memory. When sharing coefficients across H and V operations, it is only
necessary to write coefficients for the H operation. Also, when sharing coefficients
across Y and C operations, it is only necessary to write coefficients for the Y operation.
This process is permitted to take as much time as desired by the user system. This
means that worst case, for a 12H-tap x 12V-tap 64-phase filter, you need to write 6
times per phase. If the user has specified separate H and V coefficients and separate Y
and C coefficients, this is a total of
1536 write operations per set.
• Writing a new address to
coef_set_addr
resets the internal state-machine that
oversees the coefficient loading procedure. An error condition will be asserted if the
loading procedure comes up less than
2 x
max_phases*Max(num_h_taps
,
num_v_taps
) when
coef_set_addr
is updated.
Examples of Coefficient Set Generation and Loading
As mentioned, when data is fed in raster format, coefficient 0 is applied to the lowest tap in
the aperture for the Vertical filter or for the right-most tap in the Horizontal filter.
Following are a few examples of how to generate some coefficients and translate them into
the correct format for downloading to the scaler.
Example 1: Num_h_taps = num_v_taps = 8; max_phases = 4
Table 8-1 shows a set of coefficients drawn from a sinc function.
In this example, a 32-point 1-D sinc function has been sub-sampled to generate four phases
of eight coefficients each. Sub-sampling in this way usually results in a phases whose
component coefficients rarely sum to 1.0 – this will cause image distortion. The example
MATLAB
®
m-code that follows shows how to normalize the phases to unity and how to
express them as the 16-bit integers required by the hardware. For this process,
coef_width
= 16. Note that this is only pseudo code. Generation of actual coefficients is
X-Ref Target - Figure 8-3
Figure 8-3: Coefficient Loading Procedure – One Phase (8-tap filter shown)
Coef s 0,1 coef_d a t a _in
coef_wr_en
Coef s 2, 3 Coef s 4, 5 Coef s 6, 7
UG_ 3 0_0 3 1909
Table 8-1: Example 1 Decimal Coefficients
Phase Tap 0 Tap 1 Tap 2 Tap 3 Tap 4 Tap 5 Tap 6 Tap 7
0 0.0000 0.0000 0.0000 0.0000 1.0000 0.0000 0.0000 0.0000
1 -0.0600 0.0818 -0.1286 0.3001 0.9003 -0.1801 0.1000 -0.0693
2
-0.0909 0.1273 -0.2122 0.6366 0.6366 -0.2122 0.1273 -0.0909
3 -0.0693 0.1000 -0.1801 0.9003 0.3001 -0.1286 0.0818 -0.0600