Preparation
You should first have RISC-V 32-bit toolchain with Newlib -- RISC-V GNU Compiler Toolchain, probably configure with ./configure --prefix=/opt/riscv32_xxx --with-arch=rv32ima_zicsr --with-abi=ilp32 && make newlib.
Or you can use pre-built Docker containers including the tools: regymm/rv32ima
Hardware
Then run make in firmware/ to generate SoC boot ROM. Or docker run -it --rm -v .:/mnt regymm/rv32ima:latest and make -C /mnt/firmware.
If error occurs, probably it's just some minor path problems or environment variables, just export variables, modify Makefile, and fix according your own case.
Use Just create a new project and add all verilog files and constraints. See eda_projects/pCPU-squeakyboard-vivado/proj.tcl to re-create Vivado project.sim/run_sim.sh for an idea of what files are required. That's it, because no IP core is used. Clocking is (by default) instantiated via PLL or MMCM directly instead of clocking_wizard.
Of course you should modify files in rtl/board-specific/nexys_video/ according to your own board and peripherals(you can just disconnect input/output wires without disabling modules, no problem).
Then run synthesis/implementation/bitstream as usual -- just take special care that no critical warnings about result_bootrom.dat occur -- boot ROM must be compiled into bitstream, while RAM and register inital values usually don't matter. It's recommended to have ILA hooked up to ∂CPU program counter(PC) and memory buses, in case memory hangs or PC flies away.
UART
UART is recommended for interaction, program downloading, and reseting -- instead of hardware buttons, SD card, or HDMI.
Open serial port at 921600-baud with like sudo picocom -b 921600 -p 1 /dev/ttyUSB1. Picocom is recommend while screen is not -- when pasting a bunch of characters and transferring at full speed, screen seems to miss characters. Baud rate can be changed at BAUD_RATE_UART parameter in quasi_main.v
When system starts, you should see messages like these:
[bootrom]c_start
[bootrom]sdcard not found. boot from UART.
Or with firmware/sd_uartbl/uartbl.bin written to SD card's first sectors:
[bootrom]c_start
[bootrom]load from sdcard
[bootrom]xfer ctrl to 0x20000000
[uartbl] started.
Input multiple R until LED brightness changes to reset the board. Then press x (or anything else, but not 0-9a-f) to de-assert reset. So resetting can be automated without hardware intervention.
See software/uartboot.sh for program downloading details. Make sure you have a 921600-baud picocom running when using uartboot.sh, or the > /dev/ttyUSB? will suffer wrong baud rate.
Software
In software/, run make run_tests, make run_coremark, or make run_renderer for RISC-V tests, CoreMark, or the renderer. They'll be automatically compiled and downloaded via UART to Quasi SoC. You'll need HDMI for renderer.
I think these three examples can cover most of the software flows required in cross-compiling(Makefile, linker script, volatile int* MMIO, ODR, inline assembly, call C in assembly, objcopy, patch BSS, ...). My coding habit is bad but they work(at least for now).
Things like printf, string operation, float-point, and basic C++ are all tested to be working.