AN2768 Freescale Semiconductor / Motorola, AN2768 Datasheet - Page 27

• Manufacturer Part Number: AN2768
• Description: Implementation of a 128-Point FFT on the MRC6011 Device
• Manufacturer: Freescale Semiconductor / Motorola

Table 5 lists the frame buffer memory requirements of the code. The RCF frame buffer size (40 KB ) is sufficient
to meet the requirements.
Table 6 shows how the context memory in the RCF core is used in the FFT implementation. The FFT128
computation is divided into three kernels to avoid limiting the number of contexts (contexts of a kernel cannot
exceed 64). However, all contexts of the kernels can be stored in context memory, which has 128 context memory
locations for row and column contexts.
Four 128-point white noise random number sequences were used to generate the averaged errors of the FFT
spectra. The input numbers were clipped to the range of (–32768, +32767) and the errors were computed as
follows:
Freescale Semiconductor
FFT128_Transpose
FFT128_Stage1_6
FFT128_Stage7
Error
FFT128_Transpose
FFT128_Stage1_6
FFT128_Stage7
Input data
Twiddle factor
Temporary area for intermediate
result
Output data
Table 5. Memory Requirements for the 128-Point FFT Implementation on RCF
Kernel Name
) (
i
TOTAL
=
Variable Description
Table 4. RCF Cycle Counts for Separate Runs of the 128-Point FFT
sqrt
Table 6. Context Memory Usage for the 128-Point FFT on RCF
Implementation of a 128-Point FFT on the MRC6011 Device, Rev. 0
Kernel Name
TOTAL
TOTAL
([
Y
re
flt
) (
i
−
128
39
58
12
109
Number of Row Contexts
*
Y
634
1941
1084
3659
psiInputData
psiInputTwiddle
psiOutTmp
psiOutput
re
fix
(
Cycles First Run
i
Variable Name
)]
2
+
[
Y
im
flt
) (
i
−
128
512
544
256
512
1824 bytes
16
32
2
50
139
297
248
684
Number of Column Contexts
Cycles Second Run
*
Bytes Required
Y
im
fix
Performance and Error Analysis
(
i
)]
2
)
Equation 15
27