fip.bin is placed into the first partition, it contains FSBL (first stage bootloader), U-Boot, openSBI, and the compiled code for the second core (FreeRTOS), as well as set all the relevant options for the bootrom.

boot.sd is the kernel and the flattened devicetree that U-Boot will use to launch the system.

Compiler (SDCC) with nano: Here
Files related to Compiler Builds: Here

Instructions

First, build SDCC (8051 compiler) for C906 to compile on Duo.

I am using a custom compiled Toolchain (from https://github.com/riscv-collab/riscv-gnu-toolchain) BECAUSE NOTHING PREBUILT F*CKING WORKS RIGHT OMFG HOW HARD IS IT TO BUILD A WORKING GCC+GLIBC AND NOT FAIL (yes i had obscure nonsensical errors building sdcc before I rebuilt the toolchain myself, it fixed the issue, i lost like 6 hours on this, do not use the official archlinux packaged toolchain for riscv64 or any other options like that)
For milk-v's toolchain mtune and march will be different (and it might not work at all for this, havent tried), look into the buildroot for examples of them.

But we have a couple dependencies that need to be built for riscv64:

for zlib:
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=$PWD/out -DCMAKE_TOOLCHAIN_FILE=/home/vdragon/dev/DUO/toolchain_c906.cmake ..
make -j16
make install

for boost:

# Build and setup boost.build (ONLY boost.build) for your system (google)
# then:
mkdir build
cd build
./build.sh

And finally SDCC, which we build statically just to be sure:

mkdir build
cd build
# build libs for sdcc devices, we need sdcc for that and it does it by itself, so build for host
../configure --disable-pic14-port --disable-pic16-port
make -j16
make DESTDIR=$PWD/out install
rm -r $PWD/out/usr/local/bin $PWD/out/usr/local/libexec
make clean
# and then delete everything but out and our scripts becasue make has the dumbs and will try to use the x86_64 files
#build for riscv64 immediatly after
configure.sh
build.sh
make DESTDIR=$PWD/out install
Because i changed toolchain midway, my out folder is a mess, but the idea is to end up with bin, libexec, and share (the one from the host compilation) folders

Grab those files, put them in your system image in the appropriate folders (copying the 3 folders in /usr/local is a good option)
Check SDCC runs (if you didnt put it in /usr/local you might want to add that to PATH):

I also grabbed a example to test functionality:

A more up to date (1.0-beta) SG2000 datasheet: sg2000.pdf
Build date: 24/03/2024