Terminology - 2022.1 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

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2022.1 English
PL or Programmable Logic
The part of the FPGA that is made of fundamental programmable building blocks such as flip-flops registers, look-up-tables (LUTs), digital signal processing units (DSPs), RAM-based memory block or clocking circuitry. The PL region can contain one or more accelerators as defined below.
Accelerator (ACC)
Designates everything that is custom-generated by the VSC mode and sits inside the programmable logic of the FPGA or ACAP device. The accelerator contains one or more replicated compute units (CUs) in the hardware. In some situations, the term accelerator might also be loosely used to describe the whole Programmable Logic design also including the platform and/or .xo kernels generated by the Vitis compile flow. The VSC accelerator is specified in a user-defined C++ class derived from a predefined VPP_ACC class. The interface specification contains connections into Vitis platform ports to access the peripheral resources such an global memories or ethernet ports. The accelerator also contains data movers, which are IP designed to efficiently move data from global memory to the compute units and back.
Compute Unit (CU)
Designates the composition of one or more processing elements (PEs) as defined below, that connect to global memory and streams to move data to other PEs. The interface is described using the compute() method in the accelerator class. This named API acts as the software entry-point function to the accelerator and therefore specifies the hardware-software arguments. The CU makes the system composition self-describing from the source code and not via the use of text config files.
Processing Element (PE)
Designates the core building block of a compute functionality that performs specific actions on data. This is a function-call within the scope of the of the compute() method in the accelerator class. The processing element's functionality can be written in C++ and each PE is compiled by individually by Vitis HLS.
Refers to a method of assembling PEs to form a structural network for a CU. The body of the compute() method semantically refers to a composition of PEs in hardware, which is unlike the procedural semantics of a C-function body. VSC will enable validation of such a specification. The PEs collectively compose a CU, and one or more replicated CUs exist in an accelerator.