1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
|
//
// Copyright 2024 Ettus Research, a National Instruments Brand
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Module: xfft_config_pkg
//
// Description:
//
// This package helps helps build and interpret the s_axis_config_tdata bus
// used to configure the Xilinx FFT core. The bus changes depending on the
// parameters of the IP. See the Xilinx Fast Fourier Transform product guide
// (PG109) for details. You can verify the values for a specific
// configuration by clicking the Implementation tab in the Vivado IP
// customization GUI.
//
package xfft_config_pkg;
// Set to 1 if cyclic prefix is enabled on the Xilinx IP. Set to 0 otherwise.
localparam bit CP_ENABLE = 0;
localparam int MAX_W = 256;
// Returns the width of the SCAL_SCH field of the config_tdata bus.
function automatic int fft_scale_w(int max_fft_size_log2);
// max_fft_size_log2 rounded up to the nearest multiple of 2
return ((max_fft_size_log2+1) / 2) * 2;
endfunction
// Returns the FFT scale value needed to get the default 1/N scaling for a
// given FFT size.
function automatic int fft_scale_default(int size_log2);
// Should be [ 10 10 ... 10] if N is a power of 4 (size_log2 is even)
// Should be [ 01 10 ... 10] if N is not a power of 4 (size log2 is odd)
int scale;
for (int i = 0; i < (size_log2+1)/2; i++) begin
scale[i*2 +: 2] = i == size_log2/2 ? 2'b01: 2'b10;
end
return scale;
endfunction
// Returns the width of the FWD_INV field of the config_tdata bus.
function automatic int fft_fwd_inv_w(int max_fft_size_log2);
return 1;
endfunction
// Returns the width of the CP_LEN field of the config_tdata bus.
function automatic int fft_cp_len_w(int max_fft_size_log2);
if (CP_ENABLE) begin
// Always the same as NFFT if present
return max_fft_size_log2;
end else begin
return 0;
end
endfunction
// Returns the width of the NFFT field of the config_tdata bus.
function automatic int fft_nfft_w(int max_fft_size_log2);
return 5;
endfunction
// Returns the LSB position of the SCAL_SCH field of the config_tdata bus.
function automatic int fft_scale_pos(int max_fft_size_log2);
return fft_fwd_inv_pos(max_fft_size_log2) + 1;
endfunction
// Returns the LSB position of the FWD_INV field of the config_tdata bus.
function automatic int fft_fwd_inv_pos(int max_fft_size_log2);
if (CP_ENABLE) begin
if (fft_cp_len_pos(max_fft_size_log2) + fft_cp_len_w(max_fft_size_log2) > 16)
return 24;
else
return 16;
end else begin
return 8;
end
endfunction
// Returns the LSB position of the CP_LEN field of the config_tdata bus.
function automatic int fft_cp_len_pos(int max_fft_size_log2);
return 8;
endfunction
// Returns the LSB position of the NFFT field of the config_tdata bus.
function automatic int fft_nfft_pos(int max_fft_size_log2);
return 0;
endfunction
// Returns the width of the config_tdata bus.
function automatic int fft_config_w(int max_fft_size_log2);
// It's the length needed to hold SCALE_SCH rounded up to the nearest byte
return ((fft_scale_w(max_fft_size_log2) + fft_scale_pos(max_fft_size_log2) + 7) / 8) * 8;
endfunction
// Generates a mask of all ones that is num_bits wide.
function automatic logic [MAX_W-1:0] mask(int num_bits);
logic [MAX_W-1:0] bits;
bits = (1 << num_bits) - 1;
return bits;
endfunction
// Builds the config_tdata value from the provided settings.
function automatic bit [MAX_W-1:0] build_fft_config(
int max_fft_size_log2,
int scale_sch,
bit fwd_inv,
int nfft,
int cp_len = 0
);
bit [MAX_W-1:0] cfg;
assert (max_fft_size_log2 >= 4 && max_fft_size_log2 <= 16) else
$fatal(1, "This FFT size is not yet supported");
assert (!CP_ENABLE || cp_len == 0) else
$fatal(1, "Cyclic prefix must be 0 if not in use");
cfg =
((scale_sch & mask(fft_scale_w (max_fft_size_log2))) << fft_scale_pos (max_fft_size_log2)) |
((fwd_inv & mask(fft_fwd_inv_w(max_fft_size_log2))) << fft_fwd_inv_pos(max_fft_size_log2)) |
((cp_len & mask(fft_cp_len_w (max_fft_size_log2))) << fft_cp_len_pos (max_fft_size_log2)) |
((nfft & mask(fft_nfft_w (max_fft_size_log2))) << fft_nfft_pos (max_fft_size_log2));
return cfg;
endfunction
//synthesis translate_off
// Takes as input the config_tdata bus and prints the settings encoding on it.
function automatic void print_fft_config(int max_fft_size_log2, logic [MAX_W-1:0] cfg);
int scale_sch, fwd_inv, cp_len, nfft;
scale_sch = (cfg >> fft_scale_pos (max_fft_size_log2)) & mask(fft_scale_w (max_fft_size_log2));
fwd_inv = (cfg >> fft_fwd_inv_pos(max_fft_size_log2)) & mask(fft_fwd_inv_w(max_fft_size_log2));
cp_len = (cfg >> fft_cp_len_pos (max_fft_size_log2)) & mask(fft_cp_len_w (max_fft_size_log2));
nfft = (cfg >> fft_nfft_pos (max_fft_size_log2)) & mask(fft_nfft_w (max_fft_size_log2));
$display("SCALE_SCH_0 : 0b%0b", scale_sch);
$display("FWD_INV_0 : %0d", fwd_inv);
if (CP_ENABLE) $display("CP_LEN : %0d", cp_len);
$display("NFFT : %0d", nfft);
endfunction
// The output of this function should match what's shown in the
// Implementation Details tab of the Xilinx Fast Fourier Transform IP
// generation wizard.
function automatic void print_fft_config_fields(int max_fft_size_log2);
$display("SCALE_SCH_0(%0d:%0d) bit%0d",
fft_scale_w(max_fft_size_log2) + fft_scale_pos(max_fft_size_log2) - 1,
fft_scale_pos(max_fft_size_log2), fft_scale_w(max_fft_size_log2));
$display("FWD_INV_0(%0d:%0d) bit%0d",
fft_fwd_inv_w(max_fft_size_log2) + fft_fwd_inv_pos(max_fft_size_log2) - 1,
fft_fwd_inv_pos(max_fft_size_log2), fft_fwd_inv_w(max_fft_size_log2));
if (CP_ENABLE) begin
$display("CP_LEN(%0d:%0d) uint%0d",
fft_cp_len_w(max_fft_size_log2) + fft_cp_len_pos(max_fft_size_log2) - 1,
fft_cp_len_pos(max_fft_size_log2), fft_cp_len_w(max_fft_size_log2));
end
$display("NFFT(%0d:%0d) uint%0d",
fft_nfft_w(max_fft_size_log2) + fft_nfft_pos(max_fft_size_log2) - 1,
fft_nfft_pos(max_fft_size_log2), fft_nfft_w(max_fft_size_log2));
endfunction
//synthesis translate_on
endpackage : xfft_config_pkg
|
