3 ms·

Cortex-M3 would be an odd choice in this day and age - the core is 20 years old at this point.

jsheard 2y ago
The "3" meaning M3 is an extrapolation from the first "0" in RP2040 meaning M0+, but if the core is that old then yeah maybe it's something else. M33 perhaps?
joezydeco 2y ago
I'd be perfectly happy with a low-power Cortex-M3 if it keeps the same price point as the RP2040. We all don't need screaming fast cores and the associated price adder.
phire 2y ago
It might be an old design, but it's not outdated. There hasn't been any major innovation in CPU design for this power/performance/feature/area target, so the Cortex-M3 is still a valid choice if you don't need/want the extra instructions. In fact, the basic design is much older, the Cortex-M3 is essentially just a stripped down ARM7TDMI 3-stage pipeline from 1994, with the new Thumb2 instructions from the ARM1156T2 and all the original 32bit instructions ripped out. Arguably, it's not that different from the original ARM1 pipeline either. The Cortex-M4 is the exact same pipeline, just with a hardware divider, DSP instructions and optional FPU. If you don't need/want those, or area is more important, the Cortex-M3 is the way to go. There is the reason why ARM still have it listed as a current design. The Cortex-M33 is probably the only thing which could be considered as innovation. The pipeline can now dual-issue some pairs of 16bit instructions, giving it a 20% IPC boost in coremark. But it's now 15% larger and uses 5% more power, so it's not a true replacement for the Cortex-M3 (though, it does seem to outperform the Cortex-M4, with the same area and lower power consumption, and it also supports the optional FPU) Though, for this exact use case, I don't they are too tight on area. And I agree that it would be nice to have an FPU and DSP instructions. So if we are lucky, that 3 actually means the Cortex-M33 and the optional FPU.

The "3" meaning M3 is an extrapolation from the first "0" in RP2040 meaning M0+, but if the core is that old then yeah maybe it's something else. M33 perhaps?

joezydeco 2y ago

I'd be perfectly happy with a low-power Cortex-M3 if it keeps the same price point as the RP2040. We all don't need screaming fast cores and the associated price adder.

phire 2y ago

It might be an old design, but it's not outdated. There hasn't been any major innovation in CPU design for this power/performance/feature/area target, so the Cortex-M3 is still a valid choice if you don't need/want the extra instructions. In fact, the basic design is much older, the Cortex-M3 is essentially just a stripped down ARM7TDMI 3-stage pipeline from 1994, with the new Thumb2 instructions from the ARM1156T2 and all the original 32bit instructions ripped out. Arguably, it's not that different from the original ARM1 pipeline either. The Cortex-M4 is the exact same pipeline, just with a hardware divider, DSP instructions and optional FPU. If you don't need/want those, or area is more important, the Cortex-M3 is the way to go. There is the reason why ARM still have it listed as a current design. The Cortex-M33 is probably the only thing which could be considered as innovation. The pipeline can now dual-issue some pairs of 16bit instructions, giving it a 20% IPC boost in coremark. But it's now 15% larger and uses 5% more power, so it's not a true replacement for the Cortex-M3 (though, it does seem to outperform the Cortex-M4, with the same area and lower power consumption, and it also supports the optional FPU) Though, for this exact use case, I don't they are too tight on area. And I agree that it would be nice to have an FPU and DSP instructions. So if we are lucky, that 3 actually means the Cortex-M33 and the optional FPU.