nexus-am/README.md

The Abstract Machine (AM)

Get Started for Memory Images (Workloads)

In this section, we demonstrate how to build memory images (base_address = 0x80000000) for simulation.

• clone nexus-am from github:

git clone https://github.com/OpenXiangShan/nexus-am.git
cd nexus-am

• enter tests or benchmark directory (using apps/coremark as an example):

cd apps/coremark
make ARCH=riscv64-xs
ls ./build # you will see .bin, .txt, *,elf

• use the ".bin" file as the memory image for RTL simulation

Here we use the DiffTest RTL-simulation framework as an example. NEMU and other designs should work similarly if the base address is 0x8000_0000.

$NOOP_HOME/build/emu -i ./build/coremark-riscv64-xs.bin

How to build benchmark flash image

Some designs have a read-only bootrom for bring-up. This section builds the bootrom (flash) image whose base address is 0x1000_0000. We will be using riscv64-xs-flash instead of riscv64-xs to fix into the new address space. Do NOT follow the steps in this section if you don't know what the bootrom means.

• enter benchmark directory (using apps/coremark as an example):

cd /apps/coremark
make ARCH=riscv64-xs-flash
ls ./build

• you will find a ".bin" file, this is a benchmark image for flash

• to add the flash image to simulation in DiffTest, you can use the -F option:

$NOOP_HOME/build/emu -F ./build/coremark-riscv64-xs-flash.bin

Explanation of multi-processor bring-up drivers

The driver consists of the following functions (implemented in am/src/xs/isa/riscv/mpe.c) :

• _mpe_init(void (*entry)()): register an entry procedure that each processor will run into after initialization

• _ncpu(): return the total number of processors

• _cpu(): return the hartID of current processor (start from 0)

• _atomic_xchg(intptr_t *addr, intptr_t newval): atomic exchange function，replace the value in *addr with newval and return the original value

• _atomic_add(intptr_t *addr, intptr_t adder) : atomic adding function，increment value in *addr with adder and return the original value

• _barrier(): barrier function，wait until all processors arrive here

(For more atomic operations, You can implement it yourself using a similar format as _atomic_add)

A simple demo is provided in tests/amtest/src/tests/mp.c Here is the instruction to build and run

cd nexus-am
make ARCH=riscv64-xs-dual mainargs='m2'
# Here m means multi-processor demo, 2 means dual core
$(PATH_OF_DUALCORE_XS)/build/emu -i build/amtest-riscv64-xs-dual.bin --diff=$(PATH_OF_DUALCORE_XS)/ready-to-run/riscv64-nemu-interpreter-dual-so

The output should be like this:

My CPU ID is 0, nrCPU is 2
My CPU ID is 1, nrCPU is 2
sum = 193 atomic_sum = 200
Finalize CPU ID: 1
sum = 193 atomic_sum = 200
Finalize CPU ID: 0

Note that both sum and atomic_sum are incremented 100 times per CPU parallelly. However, atomic_sum utilizes atomic primitive. Thus, we have sum <= 200 && atomic_sum == 200.