diff --git a/src/systemcmds/gpio/gpio.cpp b/src/systemcmds/gpio/gpio.cpp
index 2236a6d6be..8c8081b852 100644
--- a/src/systemcmds/gpio/gpio.cpp
+++ b/src/systemcmds/gpio/gpio.cpp
@@ -42,76 +42,50 @@
 #include <px4_platform_common/module.h>
 #include <px4_platform_common/px4_config.h>
 
+static void usage(const char *reason);
 
-__BEGIN_DECLS
-__EXPORT int gpio_main(int argc, char *argv[]);
-__END_DECLS
-
-
-static void
-usage(const char *reason)
-{
-	printf("FAIL\n");
-
-	if (reason != nullptr) {
-		PX4_WARN("%s", reason);
-	}
-
-	PRINT_MODULE_DESCRIPTION(
-		R"DESCR_STR(
-### Description
-This command is used to read and write GPIOs
-
-gpio read <PORT> <PIN> [PULLDOWN|PULLUP] [--force]
-gpio write <PORT> <PIN> <VALUE> [PUSHPULL|OPENDRAIN] [--force]
-
-### Examples
-Read the value on port H pin 4 configured as pullup, and it is high
-$ gpio_test read H 4 PU
-1 OK
-
-Set the output value on Port E pin 7 to high
-$ gpio_test write E 7 1 --force
-OK
-
-)DESCR_STR");
-
-}
-
-int
-gpio_main(int argc, char *argv[])
+extern "C" __EXPORT int gpio_main(int argc, char *argv[])
 {
 	if (argc < 4) {
 		usage("not enough arguments");
 		return -1;
 	}
 
-	const char* command = argv[1];
+	const char *command = argv[1];
 	bool is_read = false;
 	uint32_t mask = 0;
+
 	if (strcmp(command, "read") == 0) {
 		is_read = true;
 		mask |= GPIO_INPUT;
+
 	} else if (strcmp(command, "write") == 0) {
 		if (argc < 5) {
 			usage("not enough arguments");
 			return -1;
 		}
+
 		mask |= GPIO_OUTPUT;
+
 	} else {
 		usage("command not read or write");
 		return -1;
 	}
 
-	const char* port_string = argv[2];
+	const char *port_string = argv[2];
+
 	if (strlen(port_string) != 1) {
 		usage("port not a single character");
 	}
+
 	char port = port_string[0];
+
 	if ('A' <= port && port <= 'K') {
 		mask |= ((port - 'A') << GPIO_PORT_SHIFT) & GPIO_PORT_MASK;
+
 	} else if ('a' <= port && port <= 'k') {
 		mask |= ((port - 'a') << GPIO_PORT_SHIFT) & GPIO_PORT_MASK;
+
 	} else {
 		usage("invalid port");
 		return -1;
@@ -119,43 +93,50 @@ gpio_main(int argc, char *argv[])
 
 	char *end;
 	int32_t pin = strtol(argv[3], &end, 10);
+
 	if (errno == 0 && *end == '\0' && 0 <= pin && pin <= 15) {
 		mask |= (pin << GPIO_PIN_SHIFT) & GPIO_PIN_MASK;;
+
 	} else {
 		usage("invalid pin");
 		return -1;
 	}
 
 	bool matches_default_config = false;
-#ifdef PX4_GPIO_INIT_LIST
+#if defined(PX4_GPIO_INIT_LIST)
 	const uint32_t default_gpios[] = PX4_GPIO_INIT_LIST;
+
 	// check that GPIO matches initialization list for port/pin and input/output
 	for (uint32_t i = 0; i < arraySize(default_gpios); i++) {
 		if ((((default_gpios[i] & GPIO_INPUT) == (mask & GPIO_INPUT)) ||
-		    ((default_gpios[i] & GPIO_OUTPUT) == (mask & GPIO_OUTPUT)))
+		     ((default_gpios[i] & GPIO_OUTPUT) == (mask & GPIO_OUTPUT)))
 		    && ((default_gpios[i] & GPIO_PORT_MASK) == (mask & GPIO_PORT_MASK))
 		    && ((default_gpios[i] & GPIO_PIN_MASK) == (mask & GPIO_PIN_MASK))
-		) {
+		   ) {
 			matches_default_config = true;
 		}
 	}
-#endif
-	bool force_apply = strcasecmp(argv[argc-1], "--force") == 0;
+
+#endif // PX4_GPIO_INIT_LIST
+	bool force_apply = strcasecmp(argv[argc - 1], "--force") == 0;
 
 	if (!matches_default_config && !force_apply) {
-		usage ("does not match board initialization list, and --force not specified");
+		usage("does not match board initialization list, and --force not specified");
 		return -1;
 	}
 
 	if (is_read) {
 		if (argc >= 5) {
-			const char* extra = argv[4];
+			const char *extra = argv[4];
+
 			if (strcasecmp(extra, "PULLUP") == 0) {
 				mask |= GPIO_PULLUP;
+
 			} else if (strcasecmp(extra, "PULLDOWN") == 0) {
 				mask |= GPIO_PULLDOWN;
+
 			} else if (argc == 5 && !force_apply) {
-				usage ("extra read argument not PULLUP or PULLDOWN");
+				usage("extra read argument not PULLUP or PULLDOWN");
 				return -1;
 			}
 		}
@@ -163,19 +144,24 @@ gpio_main(int argc, char *argv[])
 		px4_arch_configgpio(mask);
 		int value = px4_arch_gpioread(mask);
 		printf("%d OK\n", value);
+
 	} else {
 		int32_t value = strtol(argv[4], &end, 10);
+
 		if (errno != 0 || *end != '\0' || (value != 0 && value != 1)) {
 			usage("value not 0 or 1");
 			return -1;
 		}
 
 		if (argc >= 6) {
-			const char* extra = argv[5];
+			const char *extra = argv[5];
+
 			if (strcasecmp(extra, "PUSHPULL") == 0) {
 				mask |= GPIO_PUSHPULL;
+
 			} else if (strcasecmp(extra, "OPENDRAIN") == 0) {
 				mask |= GPIO_OPENDRAIN;
+
 			} else if (argc == 6 && !force_apply) {
 				usage("extra write argument not PUSHPULL or OPENDRAIN");
 				return -1;
@@ -186,5 +172,35 @@ gpio_main(int argc, char *argv[])
 		px4_arch_gpiowrite(mask, value);
 		printf("OK\n");
 	}
+
 	return 0;
 }
+
+void usage(const char *reason)
+{
+	printf("FAIL\n");
+
+	if (reason != nullptr) {
+		PX4_WARN("%s", reason);
+	}
+
+	PRINT_MODULE_DESCRIPTION(
+		R"DESCR_STR(
+### Description
+This command is used to read and write GPIOs
+
+gpio read <PORT> <PIN> [PULLDOWN|PULLUP] [--force]
+gpio write <PORT> <PIN> <VALUE> [PUSHPULL|OPENDRAIN] [--force]
+
+### Examples
+Read the value on port H pin 4 configured as pullup, and it is high
+$ gpio_test read H 4 PU
+1 OK
+
+Set the output value on Port E pin 7 to high
+$ gpio_test write E 7 1 --force
+OK
+
+)DESCR_STR");
+
+}