Simulation

This page describes how to simulate Carfield to execute baremetal programs. Please first read Getting Started to make sure you have all the dependencies and initialized your repository.

We currently provide working setups for:

• Questa Advanced Simulator (QuestaSim) >= 2022.3

We plan on supporting more simulators in the future. If your situation requires it, simulating Carfield on other setups should be straightforward.

Testbench

Carfield comprises several bootable domains, that are described in the Architecture section.

Each of these domains can be independently booted by keeping the rest of the SoC asleep through the domain JTAG, or Cheshire's JTAG and Serial Link, which have access to the whole platform except for the secure domain.

Alternatively, some domains can offload baremetal programs to other domains at runtime. This is common pratice when offloading programs to the accelerator domain from the host or safe domains.

Note that while runtime offloading can be exploited by RTL simulation with reasonably-sized programs, we suggest to follow the FPGA mapping steps and use OpenMP-based offload with heterogeneous cross-compilation.

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We provide a single SystemVerilog testbench for carfield_soc that handles standalone execution of baremetal programs for each domain. The code for domain X is preloaded through simulated interface drivers. In addition, some domains can read from external memory models from their boot ROM and then jump to execution.

As for Cheshire, Carfield testbench employs physical interfaces (JTAG or Serial Link) for memory preload by default. This could increase the memory preload time (independently from the target memory: dynamic SPM, LLC-SPM, or DRAM), significantly based on the ELF size.

Since by default all domains are clock gated and isolated after POR except for the host domain (Cheshire), as described in Architecture, the testbench handles the wake-up process.

To speed up the process, the external DRAM can be initialized in simulation (namely, at time 0ns) for domain X through the make variable HYP_USER_PRELOAD. Carfield SW Stack provides automatic generation of the required *.slm files, targeting an HyperRAM configured with two physical chips. Note, this flow is not recommended during ASIC development cycle as it may hide bugs in the physical interfaces.

Passive boot

X	X_BOOTMODE	X_PRELMODE	Action
CHS, SAFED, SECD, PULPD, SPATZD	0	0	Preload through JTAG
CHS, SAFED, SECD, PULPD, SPATZD	0	1	Preload through serial link

Preloading boot modes expect an ELF executable to be passed through X_BINARY.

Autonomous boot

X	CHS_BOOTMODE	CHS_PRELMODE	Action
CHS	0	2	Preload through UART
CHS	1-3	-	Autonomous boot, see Boot ROM

Autonomous boot modes expect a disk image (GPT formatted or raw code) to be passed through X_IMAGE. For more information on how to build software for Carfield and the details on the boot process of each domain, see Software Stack.

For simulation of Carfield in other designs, or in ASIC wrappers that reside in other repositories, we provide the module carfield_vip encapsulating all verification IPs and their interfaces.

QuestaSim

After building Carfield, the design can be compiled and simulated with QuestaSim. Below, we provide an example with Serial Link passive preload of a baremetal program helloworld.car.l2.elf to be executed on the host domain (Cheshire, i.e., X=CHS):

# Initialize Carfield
make car-init-all

# Compile the design
make car-vsim-sim-build

# Preload `helloworld.car.l2.elf` in passive bootmode through serial link, then start the simulation
make car-vsim-sim-run CHS_BOOTMODE=0 CHS_PRELMODE=1 CHS_BINARY=./sw/tests/bare-metal/hostd/helloworld.car.l2.elf

The design needs to be recompiled only when hardware is changed.

To clean simulation builds, from the vsim folder run

make car-vsim-sim-clean

To display general help for each Make target, type

make help

Debugging

Per default, Questasim compilation is performance-optimised, and GUI and simulation logging are disabled. To enable full visibility, logging, and the Questa GUI, set DEBUG=1 when launching the simulation.