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This is really pretty strange. RISC-V is a respectable enough architecture, but not better than recent POWER designs, equally open. NASA has an enormous amount
by ncmncm 4y ago
This is really pretty strange.
RISC-V is a respectable enough architecture, but not better than recent POWER designs, equally open. NASA has an enormous amount of experience with POWER.
I suppose it comes down to what bidders are offering to build for them.
- justahuman74 4y agoSometimes there are documents that say why NASA chose what they chose, there might be one for this
- theteapot 4y agoFollowing article has a bit more info on motivations, although it's from SiFive guy not NASA directly -- https://www.theregister.com/2022/09/06/nasas_spaceflight_computer_risc_v/ https://www.theregister.com/2022/09/06/nasas_spaceflight_com.... Summary: more vibrant eco system over the next 5-20 years and vector math.
- ilaksh 4y agoIsn't RISC-V touted as the new open architecture going forward? Much more so these days than Power.
- ncmncm 4y agoExactly the point: not technical merit.
- snvzz 4y agoIs your claim that the POWER ISA is somehow better designed than RISC-V? I honestly do not see it.
- ncmncm 4y agoNo. It is that it is not worse, and there is already a great deal of experience with it.
- alexvoda 4y agoAnd that is not wrong. (It's not necessarily right either.) The same way in software, some esoteric language or framework might be a perfect fit for a project and yet something boring and common or something new and exciting for which it easier to find employees is the better choice. Take for example a low level programming task with the following choices: Ada and Rust (excluding other options for sake of argument), with Ada being the better fit. It may still make more sense to choose Rust because the Rust community is more vibrant and the projection for the ecosystem is also up even if it might be a worse fit for the project. Choices are not always technical and as a technical person I might disagree with the choice but I can still respect it if it is well argued.
- ksec 4y agoTechnical Merit rarely plays apart anymore. It is all about ideology or interest.
- jabl 4y agoI'm sure NASA has an enormous amount of hard-earned in-house expertise in rad-hardened electronics, hard real-time safety critical software, and related things. But how much of that knowledge is tied specifically to the POWER ISA? Not much, would be my guess. I've been following POWER at a distance, and while I'm sure the ISA itself is good enough, I'm not really convinced about the vitality of the ecosystem. The only place where serious money is being invested is in the high-end CPU's which IBM keeps developing enough to prevent their high-end captive customers from defecting. But at the lower end and embedded, it's crickets. Beyond some token efforts like the microwatt for FPGA's and an old supercomputer core design they open sourced, the whole OpenPOWER effort seems to be little more than a couple of guys producing the occasional powerpoint and press releases.
- HereIGoAgain 4y agoDepressing.
- ncmncm 4y agoCompilers have had many years of work put into generating optimal instruction sequences for POWER. That is all flushed away moving to RISC-V. Momentary "vitality of the ecosystem" just seems like a poor basis to choose the underpinnings for decades of future work. But we seem to do that every time.
- blihp 4y agoNot really... they're at opposite ends of their life cycles. POWER is a dying, dead-end[1] architecture while RISC-V is just getting started. Open sourcing something already in steep decline won't typically bring it back unless there are no other options. [1] The only people who have any incentive to invest in it going forward are those who already have significant investments in it.
- ncmncm 4y agoThere is no natural life cycle for an ISA. (I am looking at you, x86!) It is easiest to pretend there is such a thing, because we are socially attuned for that. But it is not a technical observation, but a sociological one. And, that was my point. We have maybe learned a few things about ISA design since POWER was cast. But we have also forgotten things. It is far from clear we are ahead. Most of what we learned feeds into stuff like vector units that have little to do with whatever they are bolted onto. One example is the popcount instruction, omitted from the base RISC-V, and from all chips when last I checked. It has been added to every architecture ever mainstreamed, always at great expense, but it seems hard for ISA designers to contemplate. There is a special extension just for it so it could be put into a standard "profile" without importing the entire B thing.
- blihp 4y agoTrue, from a technical standpoint. I was referring to the business standpoint as it seems like other than IBM, what businesses are still making any investments in it? (i.e. no consoles using it anymore, Apple is long gone, Motorola (spinoffs) appear to at best be phasing out etc)
- jvanderbot 4y agoLast I checked, another program feature is help from domestic customers that require rad-hard, high-performance chips. That may influence the architecture significantly. In theory, domestic customers add significant resources and speed to the program.
- MisterTea 4y agoPower? How about LEON And other rad-hard Sparc processors from Microchip (formerly Atmel)? Looking at the problem long term RISC-V makes more sense. RV has a lot of steam building behind it and we have really neat things like the Polarfire SoC and many more in the works. New tools, compilers and software support are being added every day (hell, there is a plan 9 Risc-v compiler already...) RV is the future from the look of things. Power has an EoL set of chips from NXP which were former Freescale/Motorola designs and costly server chips from IBM. Arm ate their lunch in the embedded sector and Intel in the desktop/server sector. No one is looking to build new Power chips. No one is porting to Power unless its a Raptor Computing Talos workstation or IBM box, essentially an expensive toy or big iron, niche stuff.
- Symmetry 4y agoThe molecularity of the RISC-V architecture is going to be very appealing for embedded roles like this. That flexibility can be a liability for, say, a desktop operating system but if you've got an embedded system like a space probe where you develop the hardware and software in parallel it means that you can only pay for what you use in terms of ISA features. Need 64 bit memory addressing to handle all the RAM on your graphics card but don't need the chip to have an MMU? You can do that within the RISC-V spec but not within POWER. And with RISC-V there are ways to add your own specialized instructions for your particular use case. If I were designing an open source processing for a laptop or cell phone I'd use the POWER ISA. But for a space probe I'd certainly go with RISC-V.
- snvzz 4y ago>If I were designing an open source processing for a laptop or cell phone I'd use the POWER ISA. Sure, you can license a fast POWER from IBM today. But if you were to design your own, why would you ever pick POWER?