the great advantage of risc-v is that you don't need to pay arm a license for every chip, but i think that's like 99¢ or something, which is too small to matter at the price point they're likely targeting
risc-v is better in many ways; the virtual memory architecture is much cleaner, you don't need a mode bit to switch between compressed and uncompressed instructions (which avoids all kinds of minor complications), the compressed instruction set is enormously simpler, conditional branches are usually one instruction instead of two because you don't have condition codes, and if you implement it in the same process as a similar-performance arm it uses less area and less power
it's worse in others; you don't have addressing modes with bit shifts, you don't have base+offset two-register addressing, there's no bitfield extraction instructions, you can't run rv32 code on an rv64 chip, and the compilers aren't as good. all of this means lower coremarks or dmips per mhz in an in-order chip and more verbose disassembly, but a lot of it can be fixed with instruction-set extensions, which are enormously easier in risc-v land
(ldm/stm and conditional execution is maybe a wash; they're pretty convenient for assembly, but they complicate things like exception handling, context switching, debuggers, and memory-mapped I/O, and to a great extent you can paper over the lack of them with millicode and/or macro assemblers)
but it's pretty rare that issues like these are the deciding factor in whether a product is successful. i mean we have compilers and dynamic binary translation so generally switching between instruction sets is not that hard
gigadevice's risc-v clones of popular stm32s, the gd32vf line, seem to have failed despite lower power usage. gigadevice's arm clones of the same chips (gd32f) are enormously successful
It's royalty free, which (in contrast to ARM's long and expensive licensing process, or MIPS's) allows designers and manufacturers to more cheaply and fairly enter the market. RISC-V eliminates the last true bottleneck/point of control in the CPU market.
But can one compare them? Isn’t it true that RISC-V is merely an instruction set, whereas ARM is much, much more than that - it’s a whole universe of high-quality hardware designs sold (licensed) by a private company right now. And if some other company starts selling/licensing similarly high-quality designs that use the RISC-V instructions, why would that be exciting?
That's not the point. Risc-V machines are not yet price competitive, but presumably will be at some point. This is for people who are interested enough in Risc-V to spend some time and a ~$100 on it, but not thousands of of dollars. And the main reason many people are interested in Risc-V over Arm is that it's open and license free.
People are talking about cost of licensing, but the cost of ARM are peanuts compared to cost of design and fabrication. I am not even sure if the word peanuts correctly describes it.
ARM has made changes that you no longer need some one-off fees before you start producing "certain" ARM design. You get access to it and only paid for it once you start making revenue.
RISC-V makes sense for tiny microcontroller that ships in tens of millions. Western Digital saves millions every year just by switching to RISC-V for Microcontroller used in their HDD.
RISC-V's main competition is the like of ARC and some other DSP. It is competing with ARM in certain segment ( or the old ARM embedded segment ). But it is not competing ARMv8.
Yes, it's definitely a legitimate competitor to ARM on the lower end, embedded and various specialized applications.
> RISC-V is exploding everywhere
Because it's open source. Designing your own ARM cores was and is prohibitively expensive and virtually impossible for x86. That might be a huge advantage that will allow RISC-V to supplant ARM but it's not obvious that this will happen.
I'd argue that RISC-V is only really competing with ARM when it's possible to license a complete, competitive RISC-V core implementation and integrate it into a product.
At the low end, I expect (and already see) that people can give away open source IP. But not sure this model works as well at the high end where things get a lot more difficult? While it's easy to imagine people creating high performance RISC-V cores, I think they would have to either sell processors or license the IP. That would be competition with ARM, and would be a good thing, but I don't think it is clear/obvious that using the RISC-V ISA would give any company doing that much of an advantage over ARM?
First of all: the licensing of RISC-V is much cheaper than ARM. I've seen Chinese RISC-V MCU's that only cost a dime or less. And these aren't itty-bitty 4-bit parts mind you, but comparable to ARM M0 or M4.
Secondly, there are numerous open-source RISC-V designs out there to give any company a head start and the freedom to modify it as they see fit.
That assumes that RISC-V is a competitive advantage over ARM and x86. While I have no particular grounds for pessimism about RISC-V, it seems a bit premature to assume that it's better in practice than those others.
ARM is generally more competitive in terms of price and power, less competitive in peak performance.
RISC-V would have the added price advantage of being royalty-free.
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