rocket-chip VS ibex

Hello. I'm looking into implementing RISC-V on an FPGA for a school project. The two repos I'm looking into using are the Ariane and RocketChip repos. Both look actively maintained, but RocketChip has more recent releases, and it's used by this other repo that creates a block design in Vivado with the RISC-V RTL. However, we would also like to be able to make changes to the core, and I'm afraid that scala/Chisel might be difficult to learn. Ariane looks like SystemVerilog while RocketChip is mostly Chisel. Does any have recommendations on which RISC-V repo would be good to use for a project?

You could do a trial build of an in-order Rocket RISC-V core [1] to see how much space it takes up.

[1] https://github.com/chipsalliance/rocket-chip

My definition of a RISC CPU is one that has a reduced instruction set. In other words, the category of CPU is defined by the size of the instruction set, not in how it is implemented. Consider for example RISC-V CPUs. These are defined by their open instruction set alone, in spite of the fact that many implementations of RISC-V CPUs exist: some pipelined, and some not.

More complex CPUs are typically completely out of scope for hand coding, therefore you can implement generators like: https://github.com/chipsalliance/rocket-chip

We don't have Sifive's specifically but we do have the open source cores they've historically used to design their cores: https://github.com/riscv-boom/riscv-boom https://github.com/chipsalliance/rocket-chip

This would allow you to experiment with your own chip or something like [the RocketChip generator](https://github.com/chipsalliance/rocket-chip).

https://github.com/chipsalliance/rocket-chip/blob/c7da610430f51b02ebda37f3d444674dc8f2adbf/src/main/scala/system/Configs.scala#L28

I don't know about the u74 specifically, but sifive does seem to invest in a open source risc-v core called rocket-chip.

> Right now, most devices on the market do not support the C extension

This is not true and easily verifiable.

The C extension is defacto required, the only cores that don't support it are special purpose soft cores.

C extension in the smallest IP available core https://github.com/olofk/serv?tab=readme-ov-file

Supports M and C extensions https://github.com/YosysHQ/picorv32

Another sized optimized core with C extension support https://github.com/lowrisc/ibex

C extension in the 10 cent microcontroller https://www.wch-ic.com/products/CH32V003.html

This one should get your goat, it implements as much as it can using only compressed instructions https://github.com/gsmecher/minimax

We've had people consider Ibex for space applications, well verified and has a dual-core lockstep option: https://github.com/lowRISC/ibex.

An ETH Zurich team have done a triple core lockstep version for cubesats: https://www.theregister.com/2023/10/05/riscv_microcontroller...

I definitely agree with the primary point, "building a chip that meets specfic requirements we got from the customer" is not easy and it what matters.

However, RISCV cores abound. In pretty much any computing language known to man with varying design trade-offs and capabilities. It's extremely difficult to differentiate at the RTL level at this time.

Here is a high quality, well documented, SystemVerilog version intended for embedded applications that I know has been included in multiple ASIC and FPGA designs successfully.

https://github.com/lowRISC/ibex

lowRISC's (www.lowrisc.org) mission is to bring open source silicon to the hardware world and see it shipping in volume in commercial applications. We want to see open source silicon occupy a similar position to open source software (e.g. look at Linux, it's the default choice in many applications, we'd like open source silicon to be used for similar foundational technologies in the hardware world).

Here I will just use Ibex, a risc-v processor as an example, of which the repository is here: lowrisc_ibex. There are many files in this repository and I wonder which files I need given a specific configuration (for example, the configuration of "maxperf"), and how I can combine all the necessary files together, feed them to verilator and get its verilated model? I understand that only by going through this step will I acquire necessary C++ header files to write the testbench

i think it might be worth it to post it here because lowrisc develops ibex (a open source risc-v core).

Yeah but you can have both an open source (e.g. ibex) and closed source implementations for controllers (the open source one is free and you can improve it and even close its source so competitors won't benefit from your improvements) , and you can migrate from one supplier to another without spending a lot of money on migrating the software.

I am pretty new to RISC-V and open-source hardware and just began learning and working with them as part of my research. I searched about different models that have some credible documents and research done into them and decided I would try and use the ibex as the hardware language is easier for me to follow too.

Ibex is open source and has taped out - https://github.com/lowRISC/ibex

That said we used Spike as a reference simulator for verifying Ibex (RISC-V core I work on, https://github.com/lowRISC/ibex) and we run an extensive set of random programs through it comparing its execution to Ibex's and I've not come across any major issues.