4 ms·

Genuine question: what stops most Cortex M users from adopting A64 with ILP32? Anything except existing codebases?

ChuckNorris89 5y ago
Many reasons. Cost being the biggest (64bit dies would cost way more than the 32bit ones) and power consumption (having a complex pipeline with 64bit registers isn't great when you have to run on a coin cell for a year). Similar reasons to why 8 and 16 bit micros stuck around for so long in low cost and low power devices before Cortex M0+ became cheap and frugal enough.
monocasa 5y ago
At least in the M0 range, A64 won't be competitive on a gate count basis. M0s can be ridiculously tiny, down to ~12k gates, which is how they were able to take a huge chunk out of the market that had previously been 8/16 bit processors like 8051s and the like. M33s and up might make sense as A64 cores though.
- lttlrck 5y ago
  Just 12K? That's amazing. I had to look up how many the ARM1 had in 1985: 25K! 3000nm process.
  - pjmlp 5y ago
    And it is powerfull enough to run managed environments, depending on the available storage, https://www.astrobe.com/Oberon.htm https://www.astrobe.com/Oberon.htm https://docs.microej.com/en/latest/PlatformDeveloperGuide/platformOverview.html# https://docs.microej.com/en/latest/PlatformDeveloperGuide/pl... https://tinygo.org/docs/reference/microcontrollers/trinket-m0/ https://tinygo.org/docs/reference/microcontrollers/trinket-m...
topspin 5y ago
Genuine answer: power. Power consumption is a hard constraint. The benefits of A64 have to outweigh the cost in power consumption, and the benefits just aren't there. Coin cells, small solar collectors and supercaps are among the extremely limited power sources for many Cortex M applications.
photojosh 5y ago
My current Cortex-M4 project is about 40kB of code, and it runs at 48MHz. If I needed more performance, would just get one with a higher clock-rate. 64-bit has zero advantages in this context. Also, worth mentioning that our safety-critical auditor recommends staying on 90nm or larger chips. That’s many of the Cortex chips, and the same as the original iPhone.

Many reasons. Cost being the biggest (64bit dies would cost way more than the 32bit ones) and power consumption (having a complex pipeline with 64bit registers isn't great when you have to run on a coin cell for a year). Similar reasons to why 8 and 16 bit micros stuck around for so long in low cost and low power devices before Cortex M0+ became cheap and frugal enough.

monocasa 5y ago

At least in the M0 range, A64 won't be competitive on a gate count basis. M0s can be ridiculously tiny, down to ~12k gates, which is how they were able to take a huge chunk out of the market that had previously been 8/16 bit processors like 8051s and the like. M33s and up might make sense as A64 cores though.

lttlrck 5y ago
Just 12K? That's amazing. I had to look up how many the ARM1 had in 1985: 25K! 3000nm process.
- pjmlp 5y ago
  And it is powerfull enough to run managed environments, depending on the available storage, https://www.astrobe.com/Oberon.htm https://www.astrobe.com/Oberon.htm https://docs.microej.com/en/latest/PlatformDeveloperGuide/platformOverview.html# https://docs.microej.com/en/latest/PlatformDeveloperGuide/pl... https://tinygo.org/docs/reference/microcontrollers/trinket-m0/ https://tinygo.org/docs/reference/microcontrollers/trinket-m...

topspin 5y ago

Genuine answer: power. Power consumption is a hard constraint. The benefits of A64 have to outweigh the cost in power consumption, and the benefits just aren't there. Coin cells, small solar collectors and supercaps are among the extremely limited power sources for many Cortex M applications.

photojosh 5y ago

My current Cortex-M4 project is about 40kB of code, and it runs at 48MHz. If I needed more performance, would just get one with a higher clock-rate. 64-bit has zero advantages in this context. Also, worth mentioning that our safety-critical auditor recommends staying on 90nm or larger chips. That’s many of the Cortex chips, and the same as the original iPhone.