2 ms·

So this was Apollo 1 at 3.3v: I think it was less than 3 milliwatts at full power, but easily below 1 microwatt when sleeping. For our design, I kept it mostly

So this was Apollo 1 at 3.3v: I think it was less than 3 milliwatts at full power, but easily below 1 microwatt when sleeping. For our design, I kept it mostly asleep. I also used Apollo 2, not quite as low power, but faster, better UART and it had more RAM and flash. For the UART: they added a timer to give you an interrupt when no more bytes were received (otherwise there was no interrupt because the Rx FIFO was not full). What I liked is that all peripherals were "low power"- all of them could work when the CPU was off and all could wake the CPU (well it woke on any pending interrupt). So it means it's more likely that the CPU is asleep. With STM32L, only peripherals designated low power would work while the CPU was off.

kragen 5y ago
Hmm, my first thought was, "Wow, 3000 microwatts is pretty disappointing; that's in the same ballpark as STM32L or even AVR8, though presumably the Apollo 1 was several times faster than the STM32L. I wonder if their newer chips are better; the datasheets sure claim they are." But actually that number is totally in keeping with what I'd gotten from the Apollo3 datasheet: 33 pJ per Dhrystone "instruction" at 48 MHz and 1.25 DMIPS/MHz is 1.98 mW, and then there's 0.22 mW overhead, so we'd expect about 2.2 mW. 3 is close enough, especially for an earlier-generation chip. You might get an STM32L or an ATMega328 down to a milliwatt or two in run mode, but what (theoretically!) distinguishes the Ambiq chips is not their maximum power draw, but their efficiency per instruction and their deep power down load, which is what determines their power draw at a given computational load. Limited low-power peripherals can be a huge headache, yeah. Thank you very much for sharing your knowledge!