Development of a user application and hardware kernels targeting an FPGA requires a phased development approach. Because FPGA, Versal® ACAP, and Zynq UltraScale+ MPSoC are programmable devices, building the device binary for hardware takes some time. To enable quicker iterations without having to go through the full hardware compilation flow, the Vitis™ tool provides emulation targets on which the application and kernels can be run. Compiling for emulation targets is significantly faster than compiling for the actual hardware. Additionally, emulation targets provide full visibility into the application or accelerator, thus making it easier to perform debugging. Once your design passes in emulation, then in the late stages of development you can compile and run the application on the hardware platform.
The Vitis tool provides two emulation targets:
- Software emulation (sw_emu)
- The software emulation build compiles and links quickly, and the host program runs either natively on an x86 processor or in the QEMU emulation environment. The PL kernels are natively compiled and running on the host machine. This build target lets you quickly iterate on both the host code and kernel logic.
- Hardware emulation (hw_emu)
- The host program runs in
sw_emu, natively on x86 or in the QEMU, but the kernel code is compiled into an RTL behavioral model which is run in the Vivado® simulator or other supported third-party simulators. This build and run loop takes longer but provides a cycle-accurate view of kernel logic.
Compiling and linking for either of the emulation targets is seamlessly integrated into the Vitis command line and IDE flows. You can compile your host and kernel source code for either emulation target, without making any change to the source code. For your host code, you do not need to compile differently for emulation as the same host executable or PS application ELF binary can be used in emulation. Emulation targets support most of the features including XRT APIs, buffer transfer, platform memory SP tags, kernel-to-kernel connections, etc. The following sections detail the features and requirements of both the software and hardware emulation flows.
While running emulation you can specify a number of trace options as described in Enabling Profiling in Your Application to capture design data during runtime. Any reports generated during the run are collected into the xrt.run_summary file. This collection of reports can be viewed by opening the run_summary in Vitis analyzer, and includes a Summary report, System and Platform Diagrams to illustrate the hardware design, Run Guidance offering any suggestions for improving the performance of the system, and a Profile Summary and Timeline Trace when enabled in the xrt.ini file during runtime. Refer to Using the Vitis Analyzer for additional information.