Xilinx HLS FFT IP核运行时动态配置FFT长度

如上图所示，xilinx hls的fft ip核不仅可以计算固定长度的FFT变换，还可以在运行时动态配置fft变换长度，但其可配置的长度仅限于小于等于最大长度的所有可能的2的幂，即若该fft ip可支持的最大长度为32，那么配置选项为32，16，8…
运行时实时参数的配置可通过如下方式实现

config_t fft_config;
fft_config.setDir(0);    //用来配置FFT：0正向 1反向
fft_config.setSch(0x57B);//用来设置缩放因子[01 01 01 11 10 10]
fft_config.setNfft(nfft); //用来设置FFT点数

以下是整个工程的代码，分为fft_top.h,fft_top.cpp,fft_tb.cpp，前两者为源文件（设计文件）,最后者为测试平台。在本工程示例中，fft ip可以支持的最大长度为32，我们通过运行时fft变换长度的动态配置，实现了16点fft的计算。
fft_top.h:

// 67d7842dbbe25473c3c32b93c0da8047785f30d78e8a024de1b57352245f9689
/*******************************************************************************
Vendor: Xilinx 
Associated Filename: fft_top.h
Purpose: Xilinx FFT IP-XACT IP in Vivado HLS
Revision History: September 26, 2013 - initial release
                                                
*******************************************************************************
#-  (c) Copyright 2011-2019 Xilinx, Inc. All rights reserved.
#-
#-  This file contains confidential and proprietary information
#-  of Xilinx, Inc. and is protected under U.S. and
#-  international copyright and other intellectual property
#-  laws.
#-
#-  DISCLAIMER
#-  This disclaimer is not a license and does not grant any
#-  rights to the materials distributed herewith. Except as
#-  otherwise provided in a valid license issued to you by
#-  Xilinx, and to the maximum extent permitted by applicable
#-  law: (1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND
#-  WITH ALL FAULTS, AND XILINX HEREBY DISCLAIMS ALL WARRANTIES
#-  AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, INCLUDING
#-  BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-
#-  INFRINGEMENT, OR FITNESS FOR ANY PARTICULAR PURPOSE; and
#-  (2) Xilinx shall not be liable (whether in contract or tort,
#-  including negligence, or under any other theory of
#-  liability) for any loss or damage of any kind or nature
#-  related to, arising under or in connection with these
#-  materials, including for any direct, or any indirect,
#-  special, incidental, or consequential loss or damage
#-  (including loss of data, profits, goodwill, or any type of
#-  loss or damage suffered as a result of any action brought
#-  by a third party) even if such damage or loss was
#-  reasonably foreseeable or Xilinx had been advised of the
#-  possibility of the same.
#-
#-  CRITICAL APPLICATIONS
#-  Xilinx products are not designed or intended to be fail-
#-  safe, or for use in any application requiring fail-safe
#-  performance, such as life-support or safety devices or
#-  systems, Class III medical devices, nuclear facilities,
#-  applications related to the deployment of airbags, or any
#-  other applications that could lead to death, personal
#-  injury, or severe property or environmental damage
#-  (individually and collectively, "Critical
#-  Applications"). Customer assumes the sole risk and
#-  liability of any use of Xilinx products in Critical
#-  Applications, subject only to applicable laws and
#-  regulations governing limitations on product liability.
#-
#-  THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS
#-  PART OF THIS FILE AT ALL TIMES. 
#- ************************************************************************


This file contains confidential and proprietary information of Xilinx, Inc. and 
is protected under U.S. and international copyright and other intellectual 
property laws.

DISCLAIMER
This disclaimer is not a license and does not grant any rights to the materials 
distributed herewith. Except as otherwise provided in a valid license issued to 
you by Xilinx, and to the maximum extent permitted by applicable law: 
(1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND WITH ALL FAULTS, AND XILINX 
HEREBY DISCLAIMS ALL WARRANTIES AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, 
INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-INFRINGEMENT, OR 
FITNESS FOR ANY PARTICULAR PURPOSE; and (2) Xilinx shall not be liable (whether 
in contract or tort, including negligence, or under any other theory of 
liability) for any loss or damage of any kind or nature related to, arising under 
or in connection with these materials, including for any direct, or any indirect, 
special, incidental, or consequential loss or damage (including loss of data, 
profits, goodwill, or any type of loss or damage suffered as a result of any 
action brought by a third party) even if such damage or loss was reasonably 
foreseeable or Xilinx had been advised of the possibility of the same.

CRITICAL APPLICATIONS
Xilinx products are not designed or intended to be fail-safe, or for use in any 
application requiring fail-safe performance, such as life-support or safety 
devices or systems, Class III medical devices, nuclear facilities, applications 
related to the deployment of airbags, or any other applications that could lead 
to death, personal injury, or severe property or environmental damage 
(individually and collectively, "Critical Applications"). Customer assumes the 
sole risk and liability of any use of Xilinx products in Critical Applications, 
subject only to applicable laws and regulations governing limitations on product 
liability. 

THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS PART OF THIS FILE AT 
ALL TIMES.

*******************************************************************************/

#include "ap_fixed.h"
#include "hls_fft.h"

// configurable params
const char FFT_INPUT_WIDTH                     = 16;
const char FFT_OUTPUT_WIDTH                    = FFT_INPUT_WIDTH;
const char FFT_CONFIG_WIDTH                    = 16;
const char FFT_NFFT_MAX                        = 5;
const int  FFT_LENGTH                          = 1 << FFT_NFFT_MAX; 


#include <complex>
using namespace std;

struct config1 : hls::ip_fft::params_t {
    static const unsigned ordering_opt = hls::ip_fft::natural_order;
    static const unsigned config_width = FFT_CONFIG_WIDTH;
    //static const unsigned max_nfft=4;
    static const bool has_nfft = true;
    static const unsigned max_nfft = FFT_NFFT_MAX;
};

typedef hls::ip_fft::config_t<config1> config_t;
typedef hls::ip_fft::status_t<config1> status_t;

typedef ap_fixed<FFT_INPUT_WIDTH,1> data_in_t;
typedef ap_fixed<FFT_OUTPUT_WIDTH,FFT_OUTPUT_WIDTH-FFT_INPUT_WIDTH+1> data_out_t;
typedef std::complex<data_in_t> cmpxDataIn;
typedef std::complex<data_out_t> cmpxDataOut;

void dummy_proc_fe(
    bool direction,
    config_t* config, 
    cmpxDataIn in[FFT_LENGTH], 
    cmpxDataIn out[FFT_LENGTH]);

void dummy_proc_be(
    status_t* status_in, 
    bool* ovflo,
    cmpxDataOut in[FFT_LENGTH], 
    cmpxDataOut out[FFT_LENGTH]);

void fft_top(
    bool direction,
    cmpxDataIn in[FFT_LENGTH],
    cmpxDataOut out[FFT_LENGTH],
    bool* ovflo);

这里通过static const bool has_nfft = true语句激活了运行时fft变换长度动态可配置的功能。
fft_top.cpp:

// 67d7842dbbe25473c3c32b93c0da8047785f30d78e8a024de1b57352245f9689
/*******************************************************************************
Vendor: Xilinx 
Associated Filename: fft_top.cpp
Purpose: Xilinx FFT IP-XACT IP in Vivado HLS
Revision History: September 26, 2013 - initial release
                                                
*******************************************************************************
#-  (c) Copyright 2011-2019 Xilinx, Inc. All rights reserved.
#-
#-  This file contains confidential and proprietary information
#-  of Xilinx, Inc. and is protected under U.S. and
#-  international copyright and other intellectual property
#-  laws.
#-
#-  DISCLAIMER
#-  This disclaimer is not a license and does not grant any
#-  rights to the materials distributed herewith. Except as
#-  otherwise provided in a valid license issued to you by
#-  Xilinx, and to the maximum extent permitted by applicable
#-  law: (1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND
#-  WITH ALL FAULTS, AND XILINX HEREBY DISCLAIMS ALL WARRANTIES
#-  AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, INCLUDING
#-  BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-
#-  INFRINGEMENT, OR FITNESS FOR ANY PARTICULAR PURPOSE; and
#-  (2) Xilinx shall not be liable (whether in contract or tort,
#-  including negligence, or under any other theory of
#-  liability) for any loss or damage of any kind or nature
#-  related to, arising under or in connection with these
#-  materials, including for any direct, or any indirect,
#-  special, incidental, or consequential loss or damage
#-  (including loss of data, profits, goodwill, or any type of
#-  loss or damage suffered as a result of any action brought
#-  by a third party) even if such damage or loss was
#-  reasonably foreseeable or Xilinx had been advised of the
#-  possibility of the same.
#-
#-  CRITICAL APPLICATIONS
#-  Xilinx products are not designed or intended to be fail-
#-  safe, or for use in any application requiring fail-safe
#-  performance, such as life-support or safety devices or
#-  systems, Class III medical devices, nuclear facilities,
#-  applications related to the deployment of airbags, or any
#-  other applications that could lead to death, personal
#-  injury, or severe property or environmental damage
#-  (individually and collectively, "Critical
#-  Applications"). Customer assumes the sole risk and
#-  liability of any use of Xilinx products in Critical
#-  Applications, subject only to applicable laws and
#-  regulations governing limitations on product liability.
#-
#-  THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS
#-  PART OF THIS FILE AT ALL TIMES. 
#- ************************************************************************


This file contains confidential and proprietary information of Xilinx, Inc. and 
is protected under U.S. and international copyright and other intellectual 
property laws.

DISCLAIMER
This disclaimer is not a license and does not grant any rights to the materials 
distributed herewith. Except as otherwise provided in a valid license issued to 
you by Xilinx, and to the maximum extent permitted by applicable law: 
(1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND WITH ALL FAULTS, AND XILINX 
HEREBY DISCLAIMS ALL WARRANTIES AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, 
INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-INFRINGEMENT, OR 
FITNESS FOR ANY PARTICULAR PURPOSE; and (2) Xilinx shall not be liable (whether 
in contract or tort, including negligence, or under any other theory of 
liability) for any loss or damage of any kind or nature related to, arising under 
or in connection with these materials, including for any direct, or any indirect, 
special, incidental, or consequential loss or damage (including loss of data, 
profits, goodwill, or any type of loss or damage suffered as a result of any 
action brought by a third party) even if such damage or loss was reasonably 
foreseeable or Xilinx had been advised of the possibility of the same.

CRITICAL APPLICATIONS
Xilinx products are not designed or intended to be fail-safe, or for use in any 
application requiring fail-safe performance, such as life-support or safety 
devices or systems, Class III medical devices, nuclear facilities, applications 
related to the deployment of airbags, or any other applications that could lead 
to death, personal injury, or severe property or environmental damage 
(individually and collectively, "Critical Applications"). Customer assumes the 
sole risk and liability of any use of Xilinx products in Critical Applications, 
subject only to applicable laws and regulations governing limitations on product 
liability. 

THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS PART OF THIS FILE AT 
ALL TIMES.

*******************************************************************************/


#include "fft_top.h"

void dummy_proc_fe(
    bool direction,
    config_t* config, 
    cmpxDataIn in[FFT_LENGTH], 
    cmpxDataIn out[FFT_LENGTH])
{
    int i; 
    config->setDir(direction);
    config->setSch(0xA);
    config->setNfft(4); //用来设置FFT点数
    for (i=0; i< FFT_LENGTH; i++)
        out[i] = in[i];
}

void dummy_proc_be(
    status_t* status_in, 
    bool* ovflo,
    cmpxDataOut in[FFT_LENGTH], 
    cmpxDataOut out[FFT_LENGTH])
{
    int i; 
    for (i=0; i< FFT_LENGTH; i++)
        out[i] = in[i];
    *ovflo = status_in->getOvflo() & 0x1;
}


void fft_top(
    bool direction,
    complex<data_in_t> in[FFT_LENGTH],
    complex<data_out_t> out[FFT_LENGTH],
    bool* ovflo)
{
#pragma HLS interface ap_hs port=direction
#pragma HLS interface ap_fifo depth=1 port=ovflo
#pragma HLS interface ap_fifo depth=FFT_LENGTH port=in,out
#pragma HLS data_pack variable=in
#pragma HLS data_pack variable=out
#pragma HLS dataflow
    complex<data_in_t> xn[FFT_LENGTH];
    complex<data_out_t> xk[FFT_LENGTH];
    config_t fft_config;
    status_t fft_status;
   
    dummy_proc_fe(direction, &fft_config, in, xn);
    // FFT IP
    hls::fft<config1>(xn, xk, &fft_status, &fft_config);
    dummy_proc_be(&fft_status, ovflo, xk, out);
}

在该代码中，片段

    config->setDir(direction);
    config->setSch(0xA);
    config->setNfft(4); //用来设置FFT点数

实现了运行时变换方向、缩放因子以及变换长度的配置，这里设置的变换长度为$2^4=16$
fft_tb.cpp:

// 67d7842dbbe25473c3c32b93c0da8047785f30d78e8a024de1b57352245f9689
/*******************************************************************************
Vendor: Xilinx 
Associated Filename: fft_tb.cpp
Purpose: Xilinx FFT IP-XACT IP in Vivado HLS
Revision History: September 26, 2013 - initial release
                                                
*******************************************************************************
#-  (c) Copyright 2011-2019 Xilinx, Inc. All rights reserved.
#-
#-  This file contains confidential and proprietary information
#-  of Xilinx, Inc. and is protected under U.S. and
#-  international copyright and other intellectual property
#-  laws.
#-
#-  DISCLAIMER
#-  This disclaimer is not a license and does not grant any
#-  rights to the materials distributed herewith. Except as
#-  otherwise provided in a valid license issued to you by
#-  Xilinx, and to the maximum extent permitted by applicable
#-  law: (1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND
#-  WITH ALL FAULTS, AND XILINX HEREBY DISCLAIMS ALL WARRANTIES
#-  AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, INCLUDING
#-  BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-
#-  INFRINGEMENT, OR FITNESS FOR ANY PARTICULAR PURPOSE; and
#-  (2) Xilinx shall not be liable (whether in contract or tort,
#-  including negligence, or under any other theory of
#-  liability) for any loss or damage of any kind or nature
#-  related to, arising under or in connection with these
#-  materials, including for any direct, or any indirect,
#-  special, incidental, or consequential loss or damage
#-  (including loss of data, profits, goodwill, or any type of
#-  loss or damage suffered as a result of any action brought
#-  by a third party) even if such damage or loss was
#-  reasonably foreseeable or Xilinx had been advised of the
#-  possibility of the same.
#-
#-  CRITICAL APPLICATIONS
#-  Xilinx products are not designed or intended to be fail-
#-  safe, or for use in any application requiring fail-safe
#-  performance, such as life-support or safety devices or
#-  systems, Class III medical devices, nuclear facilities,
#-  applications related to the deployment of airbags, or any
#-  other applications that could lead to death, personal
#-  injury, or severe property or environmental damage
#-  (individually and collectively, "Critical
#-  Applications"). Customer assumes the sole risk and
#-  liability of any use of Xilinx products in Critical
#-  Applications, subject only to applicable laws and
#-  regulations governing limitations on product liability.
#-
#-  THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS
#-  PART OF THIS FILE AT ALL TIMES. 
#- ************************************************************************


This file contains confidential and proprietary information of Xilinx, Inc. and 
is protected under U.S. and international copyright and other intellectual 
property laws.

DISCLAIMER
This disclaimer is not a license and does not grant any rights to the materials 
distributed herewith. Except as otherwise provided in a valid license issued to 
you by Xilinx, and to the maximum extent permitted by applicable law: 
(1) THESE MATERIALS ARE MADE AVAILABLE "AS IS" AND WITH ALL FAULTS, AND XILINX 
HEREBY DISCLAIMS ALL WARRANTIES AND CONDITIONS, EXPRESS, IMPLIED, OR STATUTORY, 
INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY, NON-INFRINGEMENT, OR 
FITNESS FOR ANY PARTICULAR PURPOSE; and (2) Xilinx shall not be liable (whether 
in contract or tort, including negligence, or under any other theory of 
liability) for any loss or damage of any kind or nature related to, arising under 
or in connection with these materials, including for any direct, or any indirect, 
special, incidental, or consequential loss or damage (including loss of data, 
profits, goodwill, or any type of loss or damage suffered as a result of any 
action brought by a third party) even if such damage or loss was reasonably 
foreseeable or Xilinx had been advised of the possibility of the same.

CRITICAL APPLICATIONS
Xilinx products are not designed or intended to be fail-safe, or for use in any 
application requiring fail-safe performance, such as life-support or safety 
devices or systems, Class III medical devices, nuclear facilities, applications 
related to the deployment of airbags, or any other applications that could lead 
to death, personal injury, or severe property or environmental damage 
(individually and collectively, "Critical Applications"). Customer assumes the 
sole risk and liability of any use of Xilinx products in Critical Applications, 
subject only to applicable laws and regulations governing limitations on product 
liability. 

THIS COPYRIGHT NOTICE AND DISCLAIMER MUST BE RETAINED AS PART OF THIS FILE AT 
ALL TIMES.

*******************************************************************************/

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include "fft_top.h"
#include <stdio.h>

#include <fstream>
#include <string>
#include <sstream>

using namespace std;

int main()
{

    cmpxDataIn xn_input[FFT_LENGTH];
    cmpxDataOut xk_output[FFT_LENGTH];
	for(int i=0;i<FFT_LENGTH;i++){
		//cout<<i/FFT_LENGTH<<endl;
		xn_input[i].real((data_in_t)((float)i/(float)FFT_LENGTH));
		xn_input[i].imag((data_in_t)((float)(-i)/(float)FFT_LENGTH));
	}
	bool ovflo;
    int FWD_INV=1;
	fft_top(FWD_INV, xn_input, xk_output, &ovflo);
    for(int i=0;i<FFT_LENGTH;i++)
    	cout<<"i="<<i<<":    "<<xk_output[i].real()<<"+"<<xk_output[i].imag()<<"j"<<endl;
    cout<<ovflo<<endl;
    return 0;

}

这里虽然数组长度为32，但是其实只有前16个数参与了16点FFT变换。可通过实验验证：
HLS仿真结果:

i=0:    0.234375+-0.234375j
i=1:    0.0628967+0.0941467j
i=2:    0.0220947+0.0533447j
i=3:    0.00775146+0.0390015j
i=4:    0+0.03125j
i=5:    -0.00518799+0.026062j
i=6:    -0.00915527+0.0220947j
i=7:    -0.0125122+0.0187378j
i=8:    -0.015625+0.015625j
i=9:    -0.0187378+0.0125122j
i=10:    -0.0220947+0.00915527j
i=11:    -0.026062+0.00518799j
i=12:    -0.03125+0j
i=13:    -0.039032+-0.00778198j
i=14:    -0.0533447+-0.0220947j
i=15:    -0.0941772+-0.0629272j
i=16:    -0.0454102+0.00408936j
i=17:    0+0j
i=18:    -0.262939+0.00195313j
i=19:    0+0j
i=20:    -0.0424805+0.00408936j
i=21:    0+0j
i=22:    -0.0351563+0.00408936j
i=23:    0+0j
i=24:    -0.0439453+0.00408936j
i=25:    0+0j
i=26:    -0.787781+0.00195313j
i=27:    0+0j
i=28:    -0.0439453+0.00408936j
i=29:    0+0j
i=30:    -0.348389+0.00195313j
i=31:    0+0j

而作为baseline的python代码如下：

if __name__=='__main__':
    x=torch.from_numpy(np.array(x))
    y=torch.from_numpy(np.array(y))
    print(x)
    print(y)
    z=torch.complex(x,y)
    print(torch.fft.fft(z)/16)

运行结果为:

tensor([ 0.2344-0.2344j,  0.0629+0.0942j,  0.0221+0.0533j,  0.0078+0.0390j,
         0.0000+0.0312j, -0.0052+0.0261j, -0.0092+0.0221j, -0.0125+0.0187j,
        -0.0156+0.0156j, -0.0187+0.0125j, -0.0221+0.0092j, -0.0261+0.0052j,
        -0.0312+0.0000j, -0.0390-0.0078j, -0.0533-0.0221j, -0.0942-0.0629j],
       dtype=torch.complex128)

可以看到，baseline的输出和HLS输出的前16个数在误差允许范围内可以认为是相同的。

最后

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