Avalon Empty Signal Doesn't Work with oneAPI Simulation

Hello,

I am trying to understand how empty signal is working on Avalon Streaming and I am using slightly modified version of streaming_data_interfaces example on SYCL++_FPGA on Github for this purpose. I get the correct results for emulation but I get constant 0 while I run simulation. Also empty signal is not created on simulation waveform. How can I fix this ?

#include <iostream>
#include <sycl/ext/intel/fpga_extensions.hpp>
#include <sycl/ext/intel/prototype/pipes_ext.hpp>
#include <sycl/sycl.hpp>

#include "exception_handler.hpp"

// limit pixel values to this value, or less
constexpr int kThreshold = 200;

// Forward declare the kernel and pipe names
// (this prevents unwanted name mangling in the optimization report)
class InStream;
class OutStream;
class Threshold;

// StreamingBeat struct enables sideband signals in Avalon streaming interface
using StreamingBeatT = sycl::ext::intel::experimental::StreamingBeat<
    unsigned char,  // type carried over this Avalon streaming interface's data
                    // signal
    true,           // enable startofpacket and endofpacket signals
    true>;         // disable the empty signal

// Pipe properties
using PipePropertiesT = decltype(sycl::ext::oneapi::experimental::properties(
    sycl::ext::intel::experimental::ready_latency<0>,
    sycl::ext::intel::experimental::bits_per_symbol<8>,
    sycl::ext::intel::experimental::uses_valid<true>,
    sycl::ext::intel::experimental::first_symbol_in_high_order_bits<true>,
    sycl::ext::intel::experimental::protocol_avalon_streaming_uses_ready));

// Image streams
using InPixelPipe = sycl::ext::intel::experimental::pipe<
    InStream,        // An identifier for the pipe
    StreamingBeatT,  // The type of data in the pipe
    0,               // The capacity of the pipe
    PipePropertiesT  // Customizable pipe properties
    >;
using OutPixelPipe = sycl::ext::intel::experimental::pipe<
    OutStream,       // An identifier for the pipe
    StreamingBeatT,  // The type of data in the pipe
    0,               // The capacity of the pipe
    PipePropertiesT  // Customizable pipe properties
    >;

// A kernel that thresholds pixel values in an image over a stream. Uses start
// of packet and end of packet signals on the streams to determine the beginning
// and end of the image.
struct ThresholdKernel {
  void operator()() const {
    bool start_of_packet = false;
    bool end_of_packet = false;

    while (!end_of_packet) {
      // Read in next pixel
      StreamingBeatT in_beat = InPixelPipe::read();
      auto pixel = in_beat.data;
      start_of_packet = in_beat.sop;
      end_of_packet = in_beat.eop;
      int empty = in_beat.empty;

      // Threshold
      if (pixel > kThreshold) pixel = kThreshold;

      // Write out result
      StreamingBeatT out_beat(pixel, start_of_packet, end_of_packet,empty);
      OutPixelPipe::write(out_beat);
    }
  }
};

int main() {
  try {
#if FPGA_SIMULATOR
    auto selector = sycl::ext::intel::fpga_simulator_selector_v;
#elif FPGA_HARDWARE
    auto selector = sycl::ext::intel::fpga_selector_v;
#else  // #if FPGA_EMULATOR
    auto selector = sycl::ext::intel::fpga_emulator_selector_v;
#endif
    sycl::queue q(selector, fpga_tools::exception_handler);

    auto device = q.get_device();
    std::cout << "Running on device: "
              << device.get_info<sycl::info::device::name>().c_str()
              << std::endl;

    // Test image dimensions
    unsigned int width = 16;
    unsigned int height = 16;

    // Generate pixel data
    for (int i = 0; i < (width * height); ++i) {
      bool start_of_packet = (i == 0);
      bool end_of_packet = (i == ((width * height) - 1));
      int empty = i;
      StreamingBeatT in_beat(i, start_of_packet, end_of_packet, empty);
      InPixelPipe::write(q, in_beat);
    }

    // Call the kernel  
    q.single_task<Threshold>(ThresholdKernel{});

    // Check that output pixels are below the threshold
    bool passed = true;
    int empty ;
    for (int i = 0; i < (width * height); ++i) {
      StreamingBeatT out_beat = OutPixelPipe::read(q);
      passed &= (out_beat.data <= kThreshold);
      empty = out_beat.empty;
      std::cout<<empty<<std::endl;
    }

    std::cout << (passed ? "PASSED" : "FAILED") << std::endl;
    return passed ? EXIT_SUCCESS : EXIT_FAILURE;

  } catch (sycl::exception const &e) {
    // Catches exceptions in the host code
    std::cerr << "Caught a SYCL host exception:\n" << e.what() << "\n";
    std::terminate();
  }
}