bench_pm: Helper application for testing pm behavior

[jnohlgard]

The application assists in measuring wake up delays and for measuring power consumption of different low power modes. A logic analyzer or oscilloscope is required for taking any measurements.

This application was used to test the GPIO interrupt optimizations in RIOT-OS/RIOT#8558

Works out of the box on any board which defines BTN0_PIN which is used as a wake up trigger.

A special "coma mode" is used when building with CFLAGS=-DCOMA_MODE, this will make the application skip initialization of wake up sources and go to the lowest power mode without waking up. This mode is specifically designed to measure the baseline power consumption, to use as a reference when comparing different hardware settings and software changes.

[smlng]

Minor comments, look good to me - untested ACK

[jnohlgard]

addressed comments

[jnohlgard]

Updated:

• Cleaned up defines for pins, better general platform support.
• Added "coma mode" which runs pm_set(0) in a tight loop without any additional wake up sources, to get a good reference for the minimum achievable power consumption.

[kaspar030]

I've had some boards that made it really difficult to re-attach a debugger when going to deep sleep too fast.
Could we maybe guard this, either by a second delay or using something like while (gpio_read(BUTTON1)) {}?

[kaspar030]

some boards that made it really difficult to re-attach a debugger

Like, the only way was to do "while true; do make -C examples/hello-world flash; done" and hammering the reset button, hoping to hop into the short time from reset to CPU stop...

[jnohlgard]

And reset_config connect_assert_srst and a recent openocd did not help?
(including the important improvement bb976e3c387bc82e20ab7304f0cfac3e5eede3a1 in https://repo.or.cz/openocd.git/commit/bb976e3c387bc82e20ab7304f0cfac3e5eede3a1 if you are using a CMSIS-DAP debugger)