How to drive an output GPIO as HIGH even during sleep / suspend ?

[Dinesh K]

Hi ST Community,

We are using STM32MP157C-DK2 board and OpenSTlinux Firmware (v3.1-Openstlinux-5-4-dunfell-mp1-20-11-12) for our development. We have a requirement to drive the Blue LED (LD8) always ON even during sleep / suspend. Currently the GPIO PD11 connected to the LED becomes LOW when we issue "systemctl suspend" command in Linux.

Below is the DTS snippet:

     led {

        compatible = "gpio-leds";

        led-blue {

            label = "heartbeat";

            gpios = <&gpiod 11 GPIO_ACTIVE_HIGH>;

            linux,default-trigger = "heartbeat";

            default-state = "off";

            retain-state-suspended;

        };

    };

[Uwe Bonnes]

Use an external transistor to drive the LED. Static switch on the transistor by a pullup. To switch off, use the GPIO to short the Base/Gate to ground with GPIO as open Drain, switched low.

[Tesla DeLorean]

Is it actually low or just floating. You could reverse the sense of the diode and connect to VCC rather than GND, and then it would illuminate in the LOW case.

People tend not to have LEDs on or pull ups as these leech current, which you're typically looking to avoid.​

[PatrickF]

Hi,

Above answers from @Uwe Bonnes​ and @Community member​ are valid, an external pull-up resistor and a transistor are usually required if you want to have a LED forced ON by default. Note that LED will also be ON during platform reset/startup (otherwise, might need a much more complex circuitry which sound overkilling for just a LED).

I confirm that on most STM32 (including the STM32MP1 series), whenever the VDDCORE is shutdown, all the GPIOs are forced in High-Z (except obviously those which do system control and those related to backup domain such are TAMP, RTC, etc... when enabled).

To avoid a transistor, it might be possible to add a second drive pin for the LED (up to few mA like other GPIOs) by ANDing PWR_ON pin and the heartbeat GPIO using diode(s). PWR_ON signal is driven LOW in system Standby mode, even if VDDCORE is shutdown.

Need to have the LED active-low, i.e. connected to VDD.

This is just an idea, to be checked for potential side effects.

Regards,

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