NXP MCX system off

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Overview

This sample puts an NXP MCXA or MCXN SoC into system off, which is mapped to the SoC Deep Power Down mode. In Deep Power Down the CORE power domain is gated and the chip wakes through the reset routine, so a wakeup looks like a cold boot.

The sample runs CONFIG_SAMPLE_APP_TEST_CYCLES system-off cycles (default 10) and then stops, printing a final Completed N system-off cycles line so a test harness can confirm every wakeup happened. No console input is needed.

Because each wakeup is a reset, the completed-cycle counter must survive Deep Power Down. Deep Power Down gates every SRAM array, so the sample keeps the counter in retained SRAM and arms that SRAM’s low-power retention (the VBAT SRAM LDO on MCXN, the SPC SRAM retention LDO on MCXA) before powering off. On each boot it tells a wake from a cold boot apart using the reset cause reported through hwinfo (RESET_LOW_POWER_WAKE): a cold boot seeds the counter, a wake keeps counting. Once the target count is reached the sample returns without powering off, leaving the SoC awake and debuggable.

The wakeup source is configured through the WUC (Wakeup Controller) subsystem (the nxp,wuc-wuu driver). Two wakeup sources are selectable at build time:

• CONFIG_SAMPLE_SYSTEM_OFF_WAKEUP_TIMER (default) arms LPTMR0 through the counter alarm API and routes it to the core as a WUU internal-module wakeup source, so the board wakes itself after a few seconds with no external action.

• CONFIG_SAMPLE_SYSTEM_OFF_WAKEUP_BUTTON waits for a transition on a WUU external pin. The board devicetree attaches the WUU source to its wakeup button node (next to the button gpios) and aliases it as wakeup-button; the sample simply enables DT_ALIAS(wakeup_button). No sample overlay is required. A board describes it like:

  &user_button_2 {
      wakeup-ctrls = <&wuu NXP_WUU_PIN_0_FALLING_INT>;
  };
  
  / {
      aliases {
          wakeup-button = &user_button_2;
      };
  };
  

Building and Running

Build and flash the sample with the default (timer) wakeup source:

west build -b frdm_mcxn947/mcxn947/cpu0 samples/boards/nxp/mcxn_a/system_off
west flash

Sample Output

frdm_mcxn236 system off demo
Entering system off (cycle 1/10); the timer wakes it in 5 s
<the timer wakes the SoC after 5 s through the reset routine; main() restarts>
frdm_mcxn236 system off demo
Woke from system off; retained count 1/10
Entering system off (cycle 2/10); the timer wakes it in 5 s
...
frdm_mcxn236 system off demo
Woke from system off; retained count 10/10
Completed 10 system-off cycles

With CONFIG_SAMPLE_SYSTEM_OFF_WAKEUP_BUTTON each cycle instead waits for a press on the board’s wakeup button (SW2) to leave system off.

See also

System power off

WUC