This is primarily because core is primarily a teaching ISA. One of the best parts about RiscV is that you can teach a freshman level architecture class or a senior level chip building project with an ISA that is actually used. Anything powerful to run (a non built from source manually) linux will support a profile that bundles all the commonly needed instructions to be fast.

https://five-embeddev.com/riscv-bitmanip/1.0.0/bitmanip.html

I can see quite a few items on that list that imnsho should have been included in the core and for the life of me I can't see the rationale behind leaving them out. Even the most basic 8 bit CPU had various shifts and rolls baked in.

The SpacemiT K3 (https://www.spacemit.com/products/keystone/k3 https://www.cnx-software.com/2026/01/23/spacemit-k3-16-core-...) is the one everyone is waiting for. We have one in house (as usual, cannot discuss benchmarks, but it's good). Unfortunately I don't think there is anyone reputable offering pre-orders yet.

You're super lucky to have your hands on one!

If a CPU built in 1985 with a grand total of 26 000 transistors could afford it, I am pretty sure that anything built in this century could afford it too.

You'd be excluding many small CPUs which exist within other chips running very specialized code.

As profiles mandate these instructions anyway, there's no good reason to complicate the most basic RISC-V possible.

RISC-V is the ISA for everything, from the smallest such CPUs to supercomputers.

To the best of my knowledge (and Google-fu), 26K really isn't a lot of transistors for an embedded MCU - at least not a fully-featured 32-bit one comparable to a minimal RISC-V core. An ARM Cortex M0, which is pretty much the smallest thing out there, is around 10K gates => around 40K transistors. This is also around the same size as a minimal RISC-V core AFAICT.

The ARM core has a shifter, though.

There are many chips in the market that do embed 8051s for janitorial tasks, because it is small and not legally encumbered. Some chips have several non-exposed tiny embedded CPUs within.

RISC-V is replacing many of these, bringing modern tooling. There's even open source designs like SERV that fit in a corner of an already small FPGA, leaving room for other purposes.

(Although I do have to eat my words here - I didn't check that Wikipedia page, and it does actually list a ~6K RISC-V core! It's an experimental academic prototype "made from a two-dimensional material [...] crafted from molybdenum disulfide"; I don't know if that construction might allow for a more efficient transistor count and it's totally impractical - 1KHz clock speed, 1-bit ALU, etc. - for almost any purpose, but it is technically a RISC-V implementation significantly smaller than 26K)

That sounds like a microcoded RISC-V implementation, which can really be done for any ISA at the extreme expense of speed.

Maybe other CPU's have it as well, though I do not have enough information on that.

This is actually kind of counter to your point. The really tiny micro-controllers from the 80s only had 224 bits of registers. RV32E is at least twice that (16 registers*32 bits), and modern mcus generally use 2-4kbs of sram, so the overhead of a 32 bit barrel shifter is pretty minimal.

Same could be said of MIPS.

My understanding is the RISC-V raison d'etre is rather avoidance of patented/copywritten designs.

In spite of the currently mediocre RISC-V implementations, RISC-V seems to have more of a future and isn't clouded by ISA IP issues as you note.

That doesn't necessarily make it all that great for industrial use, does it?

> One of the best parts about RiscV is that you can teach a freshman level architecture class or a senior level chip building project with an ISA that is actually used.

You can also do that with Intel MCS-51 (aka 8051) or even i960. And again, having an ISA easily implementable "on a knee" by a fresh graduate doesn't says anything about its other technical merits other than being "easily implementable (when done in the most primitive way possible)".

Why did it fall to them to do it? Impressive that he did, but it shouldn't have been necessary.

https://wren.wtf/hazard3/doc/#extension-xh3bextm-section

There are also four other custom extensions implemented.