DART-MX8M suspend

From Variscite Wiki
DART-MX8M Suspend to RAM

1 Suspend to RAM

This state offers significant power savings as everything in the system is put into a low-power state, except for memory, which is placed into the self-refresh mode to retain its contents.

To suspend to RAM execute the following command:

# pm-suspend

2 Wake up

There are many possible ways to wake up from suspend.
A few examples:
- Pushing the ON/OFF button (when present on the board)

- Pushing a button on the board which has the boolean property "wakeup-source" set in its device tree node (under gpio_keys), e.g.:

	gpio-keys {
		compatible = "gpio-keys";
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_gpio_keys>;
               ...
               back {
                       label = "Back";
                       gpios = <&gpio4 6 GPIO_ACTIVE_LOW>;
                       linux,code = <KEY_BACK>;
                       wakeup-source;
               };
	};

- Pressing the capacitive touch which has the "wakeup-source" property set in its device tree node, e.g.:

       ft5x06_ts: ft5x06_ts@38 {
               status = "disabled";
               compatible = "edt,edt-ft5x06";
               reg = <0x38>;
               reset-gpios = <&gpio4 5 GPIO_ACTIVE_LOW>;
               pinctrl-names = "default";
               pinctrl-0 = <&pinctrl_touch>;
               interrupt-parent = <&gpio1>;
               interrupts = <14 0>;
               touchscreen-size-x = <800>;
               touchscreen-size-y = <480>;
               touchscreen-inverted-x;
               touchscreen-inverted-y;
               wakeup-source;
       };

3 Measuring SOM current consumption in suspend

To measure SOM current consumption remove resistor R15 and connect ampere meter instead.
It is recommended to boot from eMMC to get accurate measurement.


To achieve minimum power consumption during suspend it is necessary to remove two resistors on the Symphony-Board related to the Ethernet jack LEDs – R79 and R80.
If assembled they back-feed the BASE_3V3 into the non-powered Ethernet PHY during suspend, increasing power consumption.