Powerfail Mitigation

Flight computers often log data on storage devices, like µSD-Cards, eMMCs or other NAND-flashes. To protect against broken file systems (or even blocks) on powerloss, we have a small powerfail mitigation subsystem to handle power failures in a way that preserves data.

A power failure event is detected by a configured gpio pin. In a devicetree, the setup for a pulled-up GPIO pin would look like this:

/ {
   chosen {
      auxspace,pfm = &button0;
   };

   buttons {
      compatible = "gpio-keys";

      button0: button_0 {
         gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
         label = "Powerfail Pin";
      };
   };
}

The subsystem is named Powerfail Mitigation, but saving and recovering state can also be of use outside of the powerloss scope. Another example of using the Powerfail Signal is to stop data loggers, when the avionic system is in a disarmed state. In this case, the pin can act as an arm signal and start the data logger, when the pin is pulled and vice-versa:

#include <aurora/lib/powerfail.h>

static int armed = 0;

static void powerfail_assert()
{
   // Gets invoked, when powerfail pin is asserted
   armed = 0;
}

static void powerfail_deassert()
{
   // Gets invoked, when powerfail pin is deasserted
   armed = 1;
}

int main(void)
{
   powerfail_setup(&powerfail_assert, &powerfail_deassert);

   // --snip--
   // use "armed" here e.g. in a loop
   // --snip--

   return 0;
}

API Reference

typedef void (*powerfail_cb_t)(void)

Powerfail callback type, invoked from ISR context.

void powerfail_setup(powerfail_cb_t assert_cb, powerfail_cb_t deassert_cb)

Initialise the powerfail mitigation subsystem.

Parameters:

• assert_cb – Optional callback invoked in ISR context after emergency state save when power failure is detected. May be NULL.

• deassert_cb – Optional callback invoked in ISR context when power is restored (pin returns to default pullup). May be NULL.