powerCheck: add power redundancy check

A parameter spcifies what the redundancy level for 5V rail supply
needs to be and a check makes sure that it's available before
taking off such that the user is aware of a broken or disconnected
redundant power module.

src/modules/commander/Arming/PreFlightCheck/checks/powerCheck.cpp

@@ -35,11 +35,24 @@
 
 #include <drivers/drv_hrt.h>
 #include <systemlib/mavlink_log.h>
+#include <lib/parameters/param.h>
 #include <uORB/Subscription.hpp>
 #include <uORB/topics/system_power.h>
 
 using namespace time_literals;
 
+unsigned int countSetBits(unsigned int n)
+{
+	unsigned int count = 0;
+
+	while (n) {
+		count += n & 1;
+		n >>= 1;
+	}
+
+	return count;
+}
+
 bool PreFlightCheck::powerCheck(orb_advert_t *mavlink_log_pub, const vehicle_status_s &status, const bool report_fail,
 				const bool prearm)
 {
@@ -79,6 +92,19 @@ bool PreFlightCheck::powerCheck(orb_advert_t *mavlink_log_pub, const vehicle_sta
 			}
 		}
 
+		int power_module_count = countSetBits(system_power.brick_valid);
+		int required_power_module_count;
+		param_get(param_find("COM_POWER_COUNT"), &required_power_module_count);
+
+		if (power_module_count < required_power_module_count) {
+			success = false;
+
+			if (report_fail) {
+				mavlink_log_critical(mavlink_log_pub, "Power redundancy not met: %d instead of %d",
+						     power_module_count, required_power_module_count);
+			}
+		}
+
 	} else {
 		if (report_fail) {
 			mavlink_log_critical(mavlink_log_pub, "system power unavailable");

src/modules/commander/commander_params.c

@@ -912,3 +912,15 @@ PARAM_DEFINE_FLOAT(COM_KILL_DISARM, 5.0f);
  * @increment 1
  */
 PARAM_DEFINE_FLOAT(COM_CPU_MAX, 90.0f);
+
+/**
+ * Required number of redundant power modules
+ *
+ * This configures a check to verify the expected number of 5V rail power supplies are present. By default only one is expected.
+ * Note: CBRK_SUPPLY_CHK disables all power checks including this one.
+ *
+ * @group Commander
+ * @min 0
+ * @max 4
+ */
+PARAM_DEFINE_INT32(COM_POWER_COUNT, 1);