RM0020 datasheet(62/69 Pages) STMICROELECTRONICS

62 / 69 page

Performance

RM0020

62/69

The number of clock cycles for third function call of the frac16/frac32 real to complex in-

place FFTs without scaling is the same as for respective float FFT plus N/16.

Table 40.

Real to complex frac16/frac32 in-place FFT, scaling on (N odd power of two)(1)

N(2)

First function

call [clock

cycles]

Second function

call [clock

cycles]

Third function

call [clock

cycles]

Improvement to

C function [-]

IPC

[-]

128

3881

3477

3450

0.97

512

17495

16492

16356

0.99

2048

81210

78233

76899

0.99

The clock cycles include bit reversing by bitrev_table_16bit and FFT computation by fft_radix4_frac32 function and

fft_real_split_frac32 function. w_table in internal flash, seed_table in internal flash, wa_table and wb_table in internal flash.

N2_REALPART set to 0.

N is FFT length.

Table 41.

Real to complex frac16/frac32 in-place FFT, scaling on (N even power of two)(1)

N(2)

First function

call [clock

cycles]

Second function

call [clock

cycles]

Third function

call [clock

cycles]

Improvement to

C function [-]

IPC

[-]

256

8887

8172

8117

0.98

1024

40376

38527

38179

0.99

4096

188384

185207

184761

0.96

The clock cycles include bit reversing by bitrev_table_16bit and FFT computation by fft_quad_frac32 function,

fft_radix2_last_stage_frac32 function and fft_real_split_frac32 function. w_table in internal flash, seed_table in internal

flash, wa_table and wb_table in internal flash. N2_REALPART set to 0.

N is FFT length.

Table 42.

Complex float windowing function(1)

N(2)

First function

call [clock

cycles]

Second function

call [clock

cycles]

Third function

call [clock

cycles]

Improvement to

C function [-]

IPC

[-]

815

666

2.0

0.99

128

1545

1295

1290

2.0

0.99

256

2991

2541

2538

2.0

0.99

512

5882

5078

5034

2.0

0.99

1024

11652

10192

10026

2.0

0.99

2048

23189

21928

21427

1.9

0.93

w vector in internal flash.

N is window length.

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