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>Thinking about computing architectures 10 years into the future No, they aren't. Otherwise, they would have selected RISC-V ISA, rather than a legacy ISA. I

by snvzz 3y ago

>Thinking about computing architectures 10 years into the future No, they aren't. Otherwise, they would have selected RISC-V ISA, rather than a legacy ISA. I am sad to see a microcontroller family I favored sabotage itself into irrelevance like this.

baybal2 3y ago
[dead]
mhh__ 3y ago
It doesn't matter at all
kragen 3y ago
i'm not convinced this matters very much 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
- snvzz 3y ago
  >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 99¢ would be a big deal for a microcontroller. I think you might have meant a different amount. >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 As far as I am aware, there is no GD32VF line. There is a few variants of GD32VF103 and that's it. They are still at their first iteration of RISC-V chips, testing the waters. Instead, I would look at WCH32V, as they have a range of RISC-V based families. >it's worse in others RISC-V always led in 64bit code density. As of the recently ratified bit manipulation and code size extensions, RISC-V does now offer higher density in 32bit too, beating ARM thumb2. >and the compilers aren't as good Potentially still the case, yet RISC-V is rapidly building the strongest ecosystem.
  - kragen 3y ago
    for a cortex-m0 microcontroller it would be a big deal, but i think this chip is probably a 15-dollar 'microcontroller', and i'm pretty sure arm charges less for the cortex-m0 i'd say 'a few variants of gdvf103' amounts to a 'gd32vf' line, but they seem to no longer be produced. maybe you're right that they'll dip back in, especially as tensions continue to build over taiwan; i was enthusiastic to see the gd32vf though admittedly i haven't actually done anything with the ones i got i agree that wch's ch32v line is extremely exciting, especially at the low end, where it reaches a 10¢ price point i've never before seen in 32-bit mcus (probably because arm's licensing fees are too high), and i should have mentioned it i agree that risc-v has always led in 64-bit code density, and that with some extensions it beats thumb-2, but actually i think it was already kind of tied with thumb-2 on code density i agree that risc-v compilers will probably eventually be better than arm compilers but i also think that if your hardware budget includes enough ram and battery to run linux it's unlikely that issues like these will be very significant this weekend i'm prototyping a jit compiler with the objective of keeping most of my code in a bytecode form that's denser than even thumb-2 or rv32c; i anticipate about 20% better code density and about a 2-4× slowdown, with on the order of 64 clocks per instruction of compilation time. i think this should mostly eliminate the rv64c code density advantage, which i agree is pretty killer. that's not why i'm doing it, of course (i love risc-v)
nightfly 3y ago
What makes you think ARM is "legacy"? There are billions of ARM devices out there and there will be billions more made
RetroTechie 3y ago
Disclaimer: kinda RISC-V fanboy myself. But market for products like these tend to have long support cycles. Even if there's a new kid on the block, there can also be a market for updated version of existing products. And following from that: entirely possible ST would introduce some RISC-V parts as well.
- snvzz 3y ago
  >But market for products like these tend to have long support cycles. I absolutely understand this, and that's exactly why it's appalling they're introducing a new line of microcontrollers today using an ISA that's already legacy.

by snvzz 3y ago

baybal2 3y ago

[dead]

mhh__ 3y ago

It doesn't matter at all

kragen 3y ago

i'm not convinced this matters very much 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

snvzz 3y ago
>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 99¢ would be a big deal for a microcontroller. I think you might have meant a different amount. >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 As far as I am aware, there is no GD32VF line. There is a few variants of GD32VF103 and that's it. They are still at their first iteration of RISC-V chips, testing the waters. Instead, I would look at WCH32V, as they have a range of RISC-V based families. >it's worse in others RISC-V always led in 64bit code density. As of the recently ratified bit manipulation and code size extensions, RISC-V does now offer higher density in 32bit too, beating ARM thumb2. >and the compilers aren't as good Potentially still the case, yet RISC-V is rapidly building the strongest ecosystem.
- kragen 3y ago
  for a cortex-m0 microcontroller it would be a big deal, but i think this chip is probably a 15-dollar 'microcontroller', and i'm pretty sure arm charges less for the cortex-m0 i'd say 'a few variants of gdvf103' amounts to a 'gd32vf' line, but they seem to no longer be produced. maybe you're right that they'll dip back in, especially as tensions continue to build over taiwan; i was enthusiastic to see the gd32vf though admittedly i haven't actually done anything with the ones i got i agree that wch's ch32v line is extremely exciting, especially at the low end, where it reaches a 10¢ price point i've never before seen in 32-bit mcus (probably because arm's licensing fees are too high), and i should have mentioned it i agree that risc-v has always led in 64-bit code density, and that with some extensions it beats thumb-2, but actually i think it was already kind of tied with thumb-2 on code density i agree that risc-v compilers will probably eventually be better than arm compilers but i also think that if your hardware budget includes enough ram and battery to run linux it's unlikely that issues like these will be very significant this weekend i'm prototyping a jit compiler with the objective of keeping most of my code in a bytecode form that's denser than even thumb-2 or rv32c; i anticipate about 20% better code density and about a 2-4× slowdown, with on the order of 64 clocks per instruction of compilation time. i think this should mostly eliminate the rv64c code density advantage, which i agree is pretty killer. that's not why i'm doing it, of course (i love risc-v)

nightfly 3y ago

What makes you think ARM is "legacy"? There are billions of ARM devices out there and there will be billions more made

RetroTechie 3y ago

Disclaimer: kinda RISC-V fanboy myself. But market for products like these tend to have long support cycles. Even if there's a new kid on the block, there can also be a market for updated version of existing products. And following from that: entirely possible ST would introduce some RISC-V parts as well.

snvzz 3y ago
>But market for products like these tend to have long support cycles. I absolutely understand this, and that's exactly why it's appalling they're introducing a new line of microcontrollers today using an ISA that's already legacy.