XRT and Vitis™ Platform Overview

Xilinx Runtime library (XRT) is an open-source easy to use software stack that facilitates management and usage of FPGA/ACAP devices. Users use familiar programming languages like C/C++ or Python to write host code which uses XRT to interact with FPGA/ACAP device. XRT exports well defined set of software APIs that work across PCIe based datacenter platforms and ZYNQ UltraScale+ MPSoC/Versal ACAP based embedded platforms. XRT is key component of Vitis™ and Alveo™ solutions.

User Application Compilation

User application is made up of host code written in C/C++/OpenCL or Python. Device code may be written in C/C++/OpenCL or VHDL/Verilog hardware description language.


User application compilation and execution

Users use Vitis™ compiler, v++ to compile and link device code for the target platform. Host code written in C/C++/OpenCL may be compiled with gcc/g++. Host code may also be written in Python OpenCL (using PyOpenCL) or Python XRT (using built-in python binding).

PCIe Based Platforms


Alveo PCIe stack

XRT supports following PCIe based devices:

  1. U200
  2. U250
  3. U280
  4. U50
  5. AWS F1
  6. U30
  7. U25
  8. VCK5000
  9. Advantech VEGA-4000/4002

PCIe based platforms are supported on x86_64, PPC64LE and AARCH64 host architectures. The platform is comprised of physical partitions called Shell and User. The Shell has two physical functions: privileged PF0 also called mgmt pf and non-privileged PF1 also called user pf. Shell provides basic infrastructure for the Alveo platform. User partition (otherwise known as PR-Region) contains user compiled binary. XRT uses Dynamic Function Exchange (DFX) to load user compiled binary to the User partition.


XRT Linux kernel driver xclmgmt binds to management physical function. Management physical function provides access to Shell components responsible for privileged operations. xclmgmt driver is organized into subdevices and handles the following functionality:

  • User compiled FPGA image (xclbin) download which involves ICAP (bitstream download) programming, clock scaling and isolation logic management.
  • Loading firmware container called xsabin which contains PLP (for 2 RP platfroms) and firmwares for embedded Microblazes. The embedded Microblazes perform the functionality of ERT and CMC.
  • Access to in-band sensors: temperature, voltage, current, power, fan RPM etc.
  • AXI Firewall management in data and control paths. AXI firewalls protect shell and PCIe from untrusted user partition.
  • Shell upgrade by programming QSPI flash constroller.
  • Device reset and recovery upon detecting AXI firewall trips or explicit request from end user.
  • Communication with user pf driver xocl via hardware mailbox. The protocol is defined mailbox.proto.rst
  • Interrupt handling for AXI Firewall and Mailbox HW IPs.
  • Device DNA (unique ID) discovery and validation.
  • DDR and HBM memory ECC handling and reporting.


XRT Linux kernel driver xocl binds to user physical function. User physical function provides access to Shell components responsible for non privileged operations. It also provides access to compute units in user partition. xocl driver is organized into subdevices and handles the following functionality which are exercised using well-defined APIs in xrt.h header file.

  • Device memory topology discovery and device memory management. The driver provides well-defined abstraction of buffer objects to the clients.
  • XDMA/QDMA memory mapped PCIe DMA engine programming and with easy to use buffer migration API.
  • Multi-process aware context management with concurrent access to device by multiple processes.
  • Compute unit execution pipeline management with the help of hardware scheduler ERT. If ERT is not available then scheduling is completely handled by xocl driver in software.
  • Interrupt handling for PCIe DMA, Compute unit completion and Mailbox messages.
  • Setting up of Address-remapper tables for direct access to host memory by kernels compiled into user partition. Direct access to host memory is enabled by Slave Bridge (SB) in the shell.
  • Buffer import and export via Linux DMA-BUF infrastructure.
  • PCIe peer-to-peer buffer mapping and sharing over PCIe bus.
  • Secure communication infrastructure for exchanging messages with xclmgmt driver.
  • Memory-to-memory (M2M) programming for moving data between device DDR, PL-RAM and HBM.


Section security.rst describes PCIe platform security and robustness in detail.

PCIe Based Hybrid Platforms


Alveo PCIe hybrid stack

U30 and VCK5000 are MPSoC and Versal platforms respectively are considered hybrid devices. They have hardedned PS subsystem with ARM APUs in the Shell. The PL fabric is exposed as user partition. The devices act as PCIe endpoint to PCIe hosts like x86_64, PPC64LE. They have two physical function architecture identical to other Alveo platforms. On these platforms the ERT subsystem is running on APU.

Zynq-7000 and ZYNQ Ultrascale+ MPSoC Based Embedded Platforms


MPSoC Embedded stack


Versal ACAP Embedded stack

XRT supports ZYNQ-7000, ZYNQ Ultrascale+ MPSoC and Versal ACAP. User can create their own embedded platforms and enable XRT with the steps described yocto.rst.

Source code and pre-built embedded platforms for the following Xilinx evaluation boards are provided:

  1. ZC706
  2. ZCU102
  3. ZCU104
  4. ZCU106
  5. VCK190

MPSoC and Versal based platforms are supported with PetaLinux based common root filesystem and common kernel. XRT Linux kernel driver zocl does the heavy lifting for the embedded platform. It handles the following functionality with well defined APIs in xrt.h and xrt_aie.h (for AIE) header files.

  • PS memory CMA buffer management and cache management. On SVM enabled platforms zocl also manages SMMU. The driver provides well-defined abstraction of buffer objects to the clients.
  • Compute unit execution pipeline management for clients.
  • User compiled FPGA image (xclbin) for platforms with Partial Reconfiguration support.
  • Buffer object import and export via DMA-BUF.
  • Interrupt handling for compute unit completion.
  • AIE array programming and graph execution.
  • If PL-DDR memory is enabled by instantiating MIG in PL, zocl provides memory management similar to PS memory.
  • ZynqMP DMA engine programming for moving data between PS DDR and PL-DDR.
  • AIE GMIO data mover programming to move data between NOC and AIE.


Section execution-model.rst provides a high level overview of execution model.