nexus-am/README.md

The Abstract Machine (AM)

How to build benchmark flash image

• clone nexus-am from github:

git clone git@github.com:OpenXiangShan/nexus-am.git

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

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

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

How to use the prepared flash image to do simulation

• assuming you have a XiangShan repo, the commit ID should be newer than 188f739de96af363761c0f2b80b95b70ad01e0fc
• make emu build
• use -F to load the image in flash:

./emu -F $AM_HOME//apps/coremark/build/coremark-riscv64-xs-flash.bin  -i ../ready-to-run/coremark-2-iteration.bin 2>debug.log

NOTE: use -i to specify the initial ram image, or a ramdom file if you do not care.

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.