HLS System Integration

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This page discusses how you can export your IP from Vitis HLS to be used in a Vivado project, and ultimately to communicate with the HLS accelerator from a Vitis software proj ect.

Modifying Your Hardware

Exporting your HLS as IP

Since our goal is to communicate with the HLS IP from software, we will add a Slave AXI connection to our HLS IP core so that it can be connected to the ARM AXI bus.

  • Run Vitis HLS and open your project from the last assignment.
  • Add a directive to your top-level hardware function. Choose the INTERFACE directive type, and change the mode to an AXI4-Lite Slave (s_axilite).
  • Set the INTERFACE of the input parameter to also be the AXI4-Lite bus.
  • Run C Synthesis.
  • Click Solution->Export RTL, and make sure the Format Selection is set to * Vivado IP (.zip)*.
  • Close Vivado HLS.
  • Unzip your IP to a folder, for example, I used unzip digitrec.zip -d lab_vitis/ip/digitrec/

Bug fix: I ran into a bug in Vitis 2020.2 that I had to fix. Look in your <ip_dir>/drivers/digitrec_v1_0/src/Makefile and look for three commented out lines that start with ‘#echo’. Remove these lines from the Makefile. See https://support.xilinx.com/s/question/0D52E00006hpYI9SAM/bug-hls-20202-generated-makefile-compilation-error-in-vitis-20202

Adding your IP to Vivado

  • Run Vivado, open your existing project, and open the block design.
  • If you do not already have a Processor System Reset IP, add one to your design. This will use the reset signal output by the processing system to reset IP in the FPGA fabric.
    • Connect the system clock ( FCLK_CLK0 from ZYNQ7 Processing System) to the slowest_sync_clk input.
    • Connect the processor reset output (FCLK_RESET0_N) to the ext_reset_in input.
  • If you do not already have an AXI Interconnect IP, add one to your design. This is the bus that will allow the ARM CPU to communicate with the IP implemented in the FPGA fabric.
    • Configure the bus to have 1 Slave Interface and 1 Master Interface.
    • Connect the PS bus master (M_AXI_GP0 from ZYNQ7 Processing System) to the S00_AXI slave port.
    • Connect your clock (FCLK_CLK0 from ZYNQ7 Processing System) to all the clock inputs (*ACLK)
    • Connect your interconnect reset (interconnect_aresetn from Processor System Reset) to the ARESETN input.
    • Connect your peripheral reset (peripheral_aresetn from Processor System Reset) to the other reset inputs (*ARESETN)
  • Add your HLS IP:
    • Open the IP catalog
      • Right-click, Add Repository
      • Navigate to the ip folder that contains your HLS IP extracted in the earlier step, and add this directory.
    • Go back to your block design and add the HLS IP to your design.
  • Connect up your HLS IP:
    • Connect the clock (FCLK_CLK0) to the clock input (ap_clk)
    • Connect the reset (peripheral_aresetn) to the reset input (ap_rst_n)
    • Connect the bus (M00_AXI from the AXI Interconnect) to the bus slave port (s_axi_control)
  • Assign an address to your HLS IP:
    • Open the Address Editor, find your IP, right-click Assign.
    • Save the block design.

  • Run Generate Bitstream.

  • Export the new XSA file and overwrite your old one.

  • Close Vivado

Communicating with your HLS IP from Software

Updating Platform Project

  • Launch Vitis and reopen your existing workspace.
  • Right-click on your platform project, and choose Update Hardware Specification. Make sure you select your new XSA file.
  • If done correctly, you should see your HLS driver located at *ps7_cortexa9_0/standalone_ps7_cortexa9_0/bsp/ps7_cortexa9_0/libsrc/digitrec_v1_0/src. Inspect the source code and locate:
    • xdigitrec_hw.h has register offsets for your IP core. If you followed the steps correctly, you should have:
      • control register (XDIGITREC_CONTROL_ADDR_AP_CTRL)
      • interrupt registers
      • return value register (XDIGITREC_CONTROL_ADDR_AP_RETURN)
      • function argument register (XDIGITREC_CONTROL_ADDR_INPUT_R_DATA) and more.
    • xdigitrec.h provides a higher-level driver interface, with functions for starting your accelerator, checking if it’s done, setting argument inputs, etc.
  • Build your platform project.

Using the Driver in Your Code

  • Include the necessary header file in your application code and write software to test that you can start your IP, wait for it to complete, and retrieve the return value.
  • You will need to initialize the HLS device driver before you can call any of the function. As with most Xilinx drivers, this is done by calling _LookupConfig, providing the device ID from xparameters.h, and then calling _CfgInitialize: 
    XDigitrec digitrec;
XDigitrec_Config* digitrec_config = XDigitrec_LookupConfig(XPAR_DIGITREC_0_DEVICE_ID);
XDigitrec_CfgInitialize(&digitrec, digitrec_config);
  • Try running the HLS accelerator and waiting for it to complete. Provide a test value and check the return value.