AN2768 Freescale Semiconductor / Motorola, AN2768 Datasheet - Page 19

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

Figure 17 shows data regrouping for stage 3 of G1 data, which has a larger butterfly span than the previous stage.
The data from cell 1 must be swapped with data in cell 3 and also for cells (2,4), (5,7), (6,8). These data exchanges
convert the butterflies in row 2 of Figure 17 into intra-cell butterflies in row 3 of the figure.
Freescale Semiconductor
G1
G0
G0
Cell →
R8{0,*}
R9{0,*}
R4{0,*}
R0{0,*}
1
G32 G64 G96 G16 G48 G80 G112 G8
G64 G32 G96 G16 G80 G48 G112 G8
Figure 16. Data Regrouping for Stage 2 of Butterfly Operations for Group 1 Data
G[ 0]r
G[ 0]i
G[ 64]r
G[ 64]i
Implementation of a 128-Point FFT on the MRC6011 Device, Rev. 0
1
2
G[ 32]r
G[ 32]i
G[ 96]r
G[ 96]i
2
3
G[ 16]r
G[ 16]i
G[ 80]r
G[ 80]i
3
4
G[ 48]r
G[ 48]i
G[ 112]r
G[ 112]i
4
5
G[ 8]r
G[ 8]i
G[ 72]r
G[ 72]i
G40 G72 G104 G24 G56 G88 G120
G72 G40 G104 G24 G88 G56 G120
5
G[ 40]r
G[ 40]i
G[ 104]r
G[ 104]i
6
6
The FFT on the MRC6011 Device
G[ 24]r
G[ 24]i
G[ 88]r
G[ 88]i
7
7
G[ 56]r
G[ 56]i
G[ 120]r
G[ 120]i
8
8
19