Concepts

Register Transfer Level (RTL) code

RTL is code that describes the behaviour of computational hardware. It contains constructs like modules, input and output ports, signals, registers and low-level operations. Typical RTL languages are Verilog and VHDL. An example of Verilog is shown below. Electronic design automation (EDA) tools can turn RTL into descriptions of physically realizable circuits, which can be flashed onto an FPGA or taped out as an ASIC.

module foo(
  input a,
  input b,
  output c
);
  assign c = a || b;
endmodule

RTL Generator

An RTL generator produces a blob of RTL given some high level architectural parameters. This allows you to easily create customized RTL that is specialized for a given application or use case without having to redesign the whole system. Tensil contains an RTL generator for ML accelerators.

Chisel

Tensil’s RTL generator is built using Chisel, a next generation hardware design language developed out of UC Berkeley. From the Chisel website:

Chisel is a hardware design language that facilitates advanced circuit generation and design reuse for both ASIC and FPGA digital logic designs. Chisel adds hardware construction primitives to the Scala programming language, providing designers with the power of a modern programming language to write complex, parameterizable circuit generators that produce synthesizable Verilog. This generator methodology enables the creation of re-usable components and libraries, such as the FIFO queue and arbiters in the Chisel Standard Library, raising the level of abstraction in design while retaining fine-grained control.    – Source: https://www.chisel-lang.org/, retrieved 2022/03/04

Model compiler

A model compiler takes an ML model and a target architecture and produces binary artifacts that can be executed by that architecture. In Tensil’s case, the model compiler produces three artifacts. The .tprog file is the executable containing instructions to be interpreted by the accelerator, the .tdata file contains the model’s parameters in the appropriate format, and the .tmodel file tells the driver how to set up inputs and outputs.

Driver

A driver takes an architecture description and a compiled model and interacts with the abstractions in the operating system or execution environment (i.e. low-level libraries) to feed the compiled model into the hardware. It is also responsible for setting up inputs and outputs, and managing any other resources that might be revelant on a given hardware platform.