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Best Practice

Best Practice — Best practices for the HDL Coder workflow with Simulink-programmable FPGA I/O modules.

Introduction

The following best practices are intended to help you avoid common errors and get your design running as fast as possible.

Referenced Models

You can place the generated FPGA subsystem in a referenced model. Ensure Underspecified initialization detection is set to Classic in the Data Validity section of the model configuration parameters. This setting must be applied in the top model and in the referenced model so that the FPGA driver blocks will execute in the correct order on the target machine.

Two-Stage Synchronization of Digital Inputs

Asynchronous digital input signals can cause undefined logic states if not synchronized properly. Place a delay of 2 clock ticks directly after each digital input in order to synchronize the external signal and avoid meta stability.

Refer to one of the following models for examples. Note that for the IO33x-21, the delay is located within the For Each Subsystem.

Concurrent Task Execution on CPU

Avoid running multiple driver blocks which access the same FPGA I/O module in concurrently executed tasks on multiple CPU cores. This will prevent simultaneous access to the same hardware resource, which can lead to unexpected behavior.

Accelerated Bitstream Generation

Enable IP caching in the Create Project step of the HDL Coder Workflow Advisor to speed up the synthesis time of your design. The synthesis tool will use the IP cache of the reference design to reduce the synthesis time: IP Caching for Faster Reference Design Synthesis.

Use design checkpoints to speed up the build time of your bitstream. Vivado can use design checkpoints from a previous build to generate a bitstream faster, providing only a few changes have been made to the design. This option can be enabled in the Build FPGA Bitstream task of the Workflow Advisor: HDL Workflow Advisor Tasks: Build FPGA Bitstream.

FPGA and CPU Synchronization

You can use the Interrupt Interface to synchronize the CPU model with the FPGA clock. By default, the user model on the FPGA is only enabled when the model execution on the CPU starts. You must run the FPGA in free-running mode if you are using interrupts generated on the FPGA to trigger the model execution on the CPU. Disable the Run FPGA only when target application runs option in the IO3xx Setup block. The block is located within the green FPGA subsystem of the generated Simulink Real-Time model.