Introduction

PULP systems support integration of hardware accelerators (Hardware Processing Engines) that share memory with the RISC-V core and are programmed through memory-mapped load/store accesses. The hw/ips/hwpe-stream and hw/ips/hwpe-ctrl folders contain the IPs necessary to plug streaming accelerators into a PULP system on the data and control plane. For further information on how to design and integrate such accelerators, see https://hwpe-doc.rtfd.io/.

This testbench provides an example "almost standalone" environment to test an example HWPE, performing multiply-accumulate on a vector of fixed-point values (in hw/ips/hwpe-mac-engine after updating the IPs: see below in the Getting Started section). The testbench makes use of dummy memories and of a simple zero-riscy core to execute tests written directly in C, essentially in the same way one would write a test running on a real PULP system. The C testbench is located in sw/tb_hwpe.c, along with the boot script (crt0.S and vectors.S), the linker script (link.ld) and the headers (archi_hwpe.h and hal_hwpe.h). The top RTL testbench is located in hw/rtl/tb_hwpe.sv.

Getting Started

Prerequisites

This testbench requires a RISC-V GCC toolchain available and installed, for example https://github.com/pulp-platform/pulp-riscv-gnu-toolchain (the one used for testing it -- but another toolchain should be fine). The toolchain path must be exported like in the PULP SDK, i.e.,

export PULP_RISCV_GCC_TOOLCHAIN=/path/to/riscv/gcc/root

The testbench will look for the toolchain in $PULP_RISCV_GCC_TOOLCHAIN/bin.

Building the RTL simulation platform

To build the RTL simulation platform, start by getting the latest version of the IPs composing the PULP system:

make update-ips

This will download all the required IPs, solve dependencies and generate the simulation scripts using Bender, which will be installed if not already available.

After having access to the SDK, you can build the simulation platform by doing the following:

make build-hw

Running the testbench

Once built, the SW test can be built by using the command:

make clean all

Then, it is run in command-line mode by using:

make run

and in GUI mode by using

make run gui=1

All Makefile commands can be combined together as usual. Two flags can be set to alter the way that the test runs:

• P_STALL (default 0.0, max 1.0) is the probability of a fake contention in the dummy memory.
• TEST_SRCS (default is sw/tb_hwpe.c) is the C file containing the main function of the SW testbench. For example,

make build-hw clean all run P_STALL=0.1 gui=1

builds the HW platform, rebuilds the SW and runs the test in GUI mode, with 10% probability of a contention (i.e. a stall) being generated on each memory interface.

HWPE interface specifications

See documentation on https://hwpe-doc.readthedocs.io.