This is a paper CPU, right? You can't actually buy an IC. Even though there's a Linux port for it and four annual conferences so far.
There seem to be too many CPU options. Multiply and divide as an option belongs down at the 50 cent 8-bit CPU that runs a microwave oven, not on something that runs Linux. Optional floating point is maybe OK, although you should be able to trap if it's not implemented and do it in software. You don't want to have zillions of builds with different option combinations. That drove MIPS users nuts.
The protection levels are still undefined; "User" mode is designed, but what happens at Supervisor, Hypervisor, and Machine mode?
If this were well-defined and cheap tablets were coming out of Shentzen using it, it would be important.
What? No, it's an Instruction Set Architecture. It's the language the CPU speaks.
> Multiply and divide as an option belongs down at the 50 cent 8-bit CPU that runs a microwave oven, not on something that runs Linux
Irrelevant, nobody has to know your CPU doesn't implement multiply/divide, not even the OS!; you trap to machine mode and life goes on. And not every RISC-V core needs to run Linux.
> but what happens at Supervisor, Hypervisor, and Machine mode?
You read the manual that exists, implement the privileged spec, and it'll run Linux. Just because it's not frozen doesn't mean that many RISC-V cores can't already boot a number of different operating systems.
> If this were well-defined and cheap tablets were coming out of Shentzen using it, it would be important.
There are already shipping products with RISC-V cpus (like in cameras). Just because you're not the customer doesn't mean this work isn't very important to other people.
There are multiple open source implementations of it available, written in hardware description languages. You can program those on to an FPGA or even make an ASIC if your budget extends to that. The http://www.lowrisc.org/ lowRisc guys are working on an ASIC if you need a real chip.
> This is a paper CPU, right? You can't actually buy an IC.
Yes you can. You just won't know about it. The open source CPU cores tend to go into things like CMOS cameras, ISPs, video processing chips, or FPGA projects.
But RISC-V is exciting because it's the first open-source ISA that really has a good chance of becoming an open 32-bit microcontroller or even a phone/tablet CPU.
There has been silicon chips taped out as university projects. No you can't buy them, but it means there's a pretty low barrier for a commercial company to produce one. But I think the compilers just needs to mature more, especially the LLVM one (which would be useful for making IDEs etc.)
I agree about too many CPU options. It's a pain with ARM Cortex, but I'm not sure of a way around it. I think this ISA is designed to go down to the Cortex M0 level (which also lacks hardware divide). Being about to trap out of it and switch to software seems like a good system - do any other processors work like that?
There seem to be too many CPU options. Multiply and divide as an option belongs down at the 50 cent 8-bit CPU that runs a microwave oven, not on something that runs Linux. Optional floating point is maybe OK, although you should be able to trap if it's not implemented and do it in software. You don't want to have zillions of builds with different option combinations. That drove MIPS users nuts.
The protection levels are still undefined; "User" mode is designed, but what happens at Supervisor, Hypervisor, and Machine mode?
If this were well-defined and cheap tablets were coming out of Shentzen using it, it would be important.