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The RISC-V spec is not finished yet. RISC-V is a modular ISA, the base ISA contains only the minimum that must be included for all architectures. The basic ISA
by avianes 6y ago
The RISC-V spec is not finished yet.
RISC-V is a modular ISA, the base ISA contains only the minimum that must be included for all architectures.
The basic ISA therefore excludes multiplications, divisions, float, atomic, SIMD, etc.
The base ISA can only be used for small, minimalistic microcontrollers.
For more advanced microcontrollers, ISA extensions add Multiplications/divisions, Float32, ... (extensions M, F, ...).
For higher performance architectures you must add ISA extensions such as Atomics, SIMD/Vectors, ... (extensions A, P/V, ...).
(I intentionally exclude some details and other extensions to illustrate the benefits of the modular ISA)
Some of these extensions have a frozen spec, and some still open.
Therefore RISC-V does not yet offer a complete solution to compete with ARM or x86.
And currently RISC-V is perfect to target microcontrollers.
However RISC-V is designed to be competitive, as the instructions are designed to be compatible with existing optimizations for modern superscalar processors architectures.
So yes, there is a chance that RISC-V will become a serious competitor in the future.
- pjmlp 6y agoOr fragmented like Linux distros, as it remains to be seen what extensions will be freely available, and certified as correctly implemented at the hardware level.
- rwmj 6y agoAll extensions published by the RISC-V Foundation will be freely available, with verification tools. Linux distributors are attempting to define a base spec (see the Unix Platform Spec group at the Foundation) which will define a minimum set of required extensions, and all other extensions will be optional and detected at runtime. We (Red Hat) are working with Debian, SUSE and Canonical on this. It's possible in future that extensions will move from optional to required if they become popular and widely implemented. Apart from embedded (where, frankly, like ARM anything goes) Linux will not be fragmented.
- pjmlp 6y agoReally? I expect a future, where like Linux and BSD downstreamers, there will be OEMs with their own proprietary extensions using them as means of business differentiation.
- rwmj 6y agoOh for sure I expect private extensions - in fact there's even a namespace for them in the RISC-V specs. A bigger problem is not private extensions, but companies adding ad hoc MSRs and instructions, and in fact one company has already done that. Most likely we'll ignore these and try to work with the companies to get them to do the right thing in future. Note that Intel also provides private extensions to their best customers. (I believe they are fused off in chips sold to general customers.)
- avianes 6y agoI don't really understand your comparison with linux distros. Of course extensions will be fragmented, each chip will only embed a faction of the ISA according to its range of application. But Linux distro are not made to be "modular". Can you elaborate on your thoughts?
- pjmlp 6y agoSame will happen regarding OEMs doing their own stuff (ISA extensions) that won't ever get upstream. So there will be applications or compilers only available from vendor X.
- avianes 6y agoYes, only standard extensions will be supported by all compilers. Why is this a problem? If a company needs to design its own extension for its specific application, RISC-V allows it. And it will never get upstream, because it is only relevant for this specific application. And if this application is needed by many vendors, then it means that a standard extension must be designed.
- pjmlp 6y agoThink Android, but RISC-V ISA instead.
- afiori 6y agoAndroid is not fragmented, it is easy to write applications that run well on all android versions. The problem RISC-V faces is that one or more companies start to grow a significant market with non-compliant chips, basically the browser war scenario.
- pjmlp 6y agoSaid the one that never had to deal with background activities or firmware issues across the eco-system.