Strange PYNQ Behavior: Vector Exponentiation

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1

My goal here is to basically put the function

import numpy

def vectorExponentiation(x):
    return numpy.exp(x)

Onto hardware.

I have the Vitis HLS files as folllowed:

vexp.hpp:

#include "ap_axi_sdata.h"
#include "hls_stream.h"

#define N 16
#define PRESCISION 32

typedef ap_axiu<32, 1, 1, 1> pkt;
typedef hls::stream< pkt > strm;

typedef float DataType;

template <typename T> void test_kernel(T in[N], T out[N]);

DataType exponential(DataType x);

vexp.cpp:

#include "vexp.hpp"

DataType exponential(DataType x)
{
	DataType sum = DataType(1);
    for (int i = PRESCISION - 1; i > 0; --i ){
    	sum = DataType(1) + x * sum / DataType(i);
    }
    return sum;
}

template <typename T> void test_kernel(T in[N], T out[N]) {
	for(int i = 0; i < N; i++){
		out[i] = exponential(in[i]);
	}
}

void vexp
(
	strm &INPUT,
	strm &OUTPUT
)
{
#pragma HLS INTERFACE axis port=INPUT
#pragma HLS INTERFACE axis port=OUTPUT

	DataType l_0[N];
	DataType out[N];

load_A:
	  for (int i = 0; i < N; i++) {
		pkt temp = INPUT.read();
		l_0[i] = temp.data;
	  }

	  test_kernel<DataType>(l_0, out);

write_C:
	for (int i = 0; i < N; i++) {
		pkt temp;
		temp.data = out[i];
		ap_uint<1> last = 0;
		if (i == N - 1) {
			last = 1;
		}
		temp.last = last;
		temp.keep = -1;
		OUTPUT.write(temp);
	}
}

vexp_tb.cpp:

#include "vexp.hpp"

void vexp_sw(DataType in[N], DataType out[N]) {
	for(int i = 0; i < N; i++){
		out[i] = exponential(in[i]);
	}
}

int main(void) {
  int i, j, err;

  DataType in[N];
  DataType out_sw[N];
  DataType out_hw[N];

  /* initiation */
  for (i = 0; i < N; i++) {
	  in[i] = DataType(i);
	  out_sw[i] = DataType(0);
	  out_hw[i] = DataType(0);
  }

  /* hardware execute */
  test_kernel<DataType>(in, out_hw);
  printf("\nHardware kernel complete\n");

  /* software execute */
  vexp_sw(in, out_sw);
  printf("\nSoftware kernel complete\n");

  err = 1;
  for(int i = 0; i < N; i++) {
	  err = out_sw[i] == out_hw[i];
	  printf("%f, %f \n", out_sw[i], out_hw[i]);
  }
  printf("\n");

  if (err == 1) {
	  printf("\nTest successful!\r\n");
  	  return 0;
  }
  printf("\nTest failed!\r\n");
  return 1;
}

And these all compile properly with vitis.

However, when executing the bitstream on vexp.ipynb on the PYNQ:

from pynq import Overlay, allocate
import pynq.lib.dma
import numpy as np

DIM=16

DATA_TYPE = np.float32

in_buffer_A = allocate(shape=(DIM,), dtype=DATA_TYPE, cacheable=False)
out_buffer_C = allocate(shape=(DIM,), dtype=DATA_TYPE, cacheable=False)
A = np.array([x for x in range(DIM)], dtype=DATA_TYPE)
C = np.zeros((DIM,), dtype=DATA_TYPE)

ol = Overlay('./design_1.bit')
ol.download()
    
dma0 = ol.axi_dma_0

np.copyto(in_buffer_A, A)
np.copyto(out_buffer_C, C)

def silicon():
    dma0.sendchannel.transfer(in_buffer_A)
    dma0.recvchannel.transfer(out_buffer_C)
    dma0.sendchannel.wait()
    dma0.recvchannel.wait()
    return out_buffer_C

def native():
    return np.exp(A)

%time golden = native()

%time FPGA = silicon()

print(FPGA)

The printed output is mainly zeros.

Also, this is the Vivado layout:
design_1-1.pdf (16.4 KB)

Am using Vitis/Vivado 2022.1 … Does anyone know what I have done wrong?

2

The IP you create, vexp_0, needs a control signal to start. You can use the axilite port instead of ap_ctrl.
The following urls can help.
GitHub - Xilinx/PYNQ-HelloWorld: This repository contains a "Hello World" introduction application to the Xilinx PYNQ framework. and GitHub - qiyangjie/Xilinx_HLS_Study_Notes: Study notes and tutorial for xilinx hls

1 Like
3

Hi @alienflip,

Did you co-simulate the IP?

If you are using floating point numbers, I would recommend you use hls::axis<float, 0, 0, 0>

as @dwosion mentioned, can you control the IP via AXI-Lite? Can you show how you are connecting the IP?

Mario

1 Like
4

I suggest the following:
1- Make sure that TLAST is synthesized (either from HLS report or from RTL code or from system integrator by expanding INPUT_r and OUTPUT_r ports.)
2- Try AXILite interface and use control flags from your PS.
3- Take a look at the tutorials mentioned in this post (because DMA is very sensitive in PYNQ, either you configure it exactly as mentioned or it won’t work):

4- Make sure that the constant is 1 :slight_smile:

1 Like