Using Auto-Restart with the Mailbox - 2024.1 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
UG1399
Release Date
2024-05-30
Version
2024.1 English

The mailbox feature provides the ability to have semi-synchronization with a software application. The mailbox is a non-blocking mechanism that updates the HLS design parameters. Any updates provided through the mailbox will be picked up the next time the design starts.

This example design uses scalar values which will be programmed from the software application, and the design will pick them at the next software call. The scalars, adder1 and adder2, will be asynchronously updated from the software application.

Configure the HLS compiler for auto-restarting mode and enable the mailbox feature using the following configuration commands:

syn.interface.s_axilite_mailbox=both
syn.interface.s_axilite_auto_restart_counter=1
syn.interface.s_axilite_sw_reset=1

This informs the tool to create the IP or kernel using the autorestart mechanisms. The example HLS design code follows:

#define DWIDTH 32
11 
12 typedef ap_axiu<DWIDTH, 0, 0, 0> pkt;
13 
14 extern "C" {
15 void krnl_stream_vdatamover(hls::stream<pkt> &in,
16     ┆   ┆   ┆   ┆   ┆ hls::stream<pkt> &out,
17     ┆   ┆   ┆   ┆   ┆ int adder1,
18     ┆   ┆   ┆   ┆   ┆ int adder2
19     ┆   ┆   ┆   ┆   ┆ ) {
20
21 #pragma HLS interface ap_ctrl_chain port=return
22 #pragma HLS INTERFACE s_axilite port=adder2
25 #pramga  HLS port=adder1 stable
   #pramga  HLS port=adder2 stable
27 bool eos = false;
28 vdatamover:
29   do {
30     // Reading a and b streaming into packets
31     pkt t1 = in.read();
32 
33     // Packet for output
34     pkt t_out;
35 
36     // Reading data from input packet
37     ap_uint<DWIDTH> in1 = t1.data;
38 
39     // Vadd operation
40     ap_uint<DWIDTH> tmpOut = in1+adder1+adder2;
41 
42     // Setting data and configuration to output packet
43     t_out.data = tmpOut;
44     t_out.last = t1.last;
45     t_out.keep = -1; // Enabling all bytes
46 
47     // Writing packet to output stream
48     out.write(t_out);
49 
50     if (t1.last) {
51     ┆ eos = true;
52     }
53   } while (eos == false);
54

Create a mailbox to update the scalars values adder1 and adder2.

Update the design parameters from the software application using the set_arg and write methods as shown below. The auto-restarting HLS design will not stop itself because there is no start and stop for a streaming interface. The module must be explicitly stopped or reset. The application code can explicitly stop the design from running using the abort() method.

// add(in1, in2, nullptr, data_size)
  xrt::kernel add(device, uuid, "krnl_stream_vadd");
  xrt::bo in1(device, data_size_bytes, add.group_id(0));
  auto in1_data = in1.map<int*>();
  xrt::bo in2(device, data_size_bytes, add.group_id(1));
  auto in2_data = in2.map<int*>();
 
  // mult(in3, nullptr, out, data_size)
  xrt::kernel mult(device, uuid, "krnl_stream_vmult");
  xrt::bo in3(device, data_size_bytes, mult.group_id(0));
  auto in3_data = in3.map<int*>();
  xrt::bo out(device, data_size_bytes, mult.group_id(2));
  auto out_data = out.map<int*>();
 
 
  xrt::kernel incr(device, uuid, "krnl_stream_vdatamover");
  int adder1 = 20;  // arbitrarily chosen to be different from 0
  int adder2 = 10;  // arbitrarily chosen to be different from 0
 
  // create run objects for re-use in loop
  xrt::run add_run(add);
  xrt::run mult_run(mult);
  std::cout <<"performing never-ending mode with infinite auto restart"<<std::endl;
  auto incr_run = incr(xrt::autostart{0}, nullptr, nullptr, adder1, adder2);

// create mailbox to programatically update the incr scalar adder
  xrt::mailbox incr_mbox(incr_run);
 
  // computed expected result
  std::vector<int> sw_out_data(data_size);
 
  std::cout << " for loop started" <<std::endl;
  bool error = false;   // indicates error in any of the iterations
  for (unsigned int cnt = 0; cnt < iter; ++cnt) {
 
    
    // Create the test data and software result
    for(size_t i = 0; i < data_size; ++i) {
      in1_data[i] = static_cast<int>(i);
      in2_data[i] = 2 * static_cast<int>(i);
      in3_data[i] = static_cast<int>(i);
      out_data[i] = 0;
      sw_out_data[i] = (in1_data[i] + in2_data[i] + adder1 + adder2) * in3_data[i];
    }
 
    // sync test data to kernel
    in1.sync(XCL_BO_SYNC_BO_TO_DEVICE);
    in2.sync(XCL_BO_SYNC_BO_TO_DEVICE);
    in3.sync(XCL_BO_SYNC_BO_TO_DEVICE);
 
    // start the pipeline
    add_run(in1, in2, nullptr, data_size);
    mult_run(in3, nullptr, out, data_size);
 
    // wait for the pipeline to finish
    add_run.wait();
    mult_run.wait();
 
    // prepare for next iteration, update the mailbox with the next
    // value of 'adder'.
    incr_mbox.set_arg(2, ++adder1); // update the mailbox
    incr_mbox.set_arg(3, --adder2); // update the mailbox
 
 
    // write the mailbox content to hw, the write will not be picked
    // up until the next iteration of the pipeline (incr).
    incr_mbox.write();  // requests sync of mailbox to hw
 
 
    // sync result from device to host
    out.sync(XCL_BO_SYNC_BO_FROM_DEVICE);
 
    // compare with expected scalar adders
    for (size_t i = 0 ; i < data_size; i++) {
      if (out_data[i] != sw_out_data[i]) {
        std::cout << "error in iteration = " << cnt
                  << " expected output = " << sw_out_data[i]
                  << " observed output = " << out_data[i]
                  << " adder1 = " << adder1 - 1
                  << " adder2 = " << adder2 + 1 << '\n';
        throw std::runtime_error("result mismatch");
      }
    }
  }
        incr_run.abort();
}