diff --git a/include/priv_gpio.h b/include/priv_gpio.h
new file mode 100644
index 0000000..eee5e18
--- /dev/null
+++ b/include/priv_gpio.h
@@ -0,0 +1,26 @@
+#ifndef PRIV_GPIO_H_
+#define PRIV_GPIO_H_
+
+#define GPIO_MODE 0
+#define GPIO_TYPE 1
+#define GPIO_PUPD 2
+#define GPIO_SPEED 3
+#define GPIO_OUT 4
+
+void gpio(uint32_t call, uint32_t port, uint32_t pin, uint32_t value) 
+{
+	register uint32_t r0 asm("r0") = call;
+	register uint32_t r1 asm("r1") = port;
+	register uint32_t r2 asm("r2") = pin;
+	register uint32_t r3 asm("r3") = value;
+
+	asm("\
+		mov r0, %0; \
+		mov r1, %1; \
+		mov r2, %2; \
+		mov r3, %3; \
+		svc 1; \
+	" :: "r" (r0), "r" (r1), "r" (r2), "r" (r3));
+}
+
+#endif // PRIV_GPIO_H_
diff --git a/src/gpio.c b/src/gpio.c
index 151779d..29ed763 100644
--- a/src/gpio.c
+++ b/src/gpio.c
@@ -20,6 +20,27 @@
 
 #include <gpio.h>
 
+void gpio_svc(uint32_t *args)
+{
+	switch (args[0]) {
+	case 0:
+		gpio_mode((GPIO_TypeDef *)args[1], args[2], args[3]);
+		break;
+	case 1:
+		gpio_type((GPIO_TypeDef *)args[1], args[2], args[3]);
+		break;
+	case 2:
+		gpio_pupd((GPIO_TypeDef *)args[1], args[2], args[3]);
+		break;
+	case 3:
+		gpio_speed((GPIO_TypeDef *)args[1], args[2], args[3]);
+		break;
+	case 4:
+		gpio_dout((GPIO_TypeDef *)args[1], args[2], args[3]);
+		break;
+	}
+}
+
 void gpio_init(void)
 {
 	// enable clocks
diff --git a/src/main.c b/src/main.c
index 8028f93..c929d16 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,6 +20,7 @@
 
 #include <clock.h>
 #include <gpio.h>
+#include <priv_gpio.h>
 #include <heap.h>
 #include <stm32l476xx.h>
 #include <task.h>
@@ -53,19 +54,29 @@ int main(void)
 void task2(void);
 void kmain(void)
 {
-	gpio_mode(GPIOA, 5, OUTPUT);
+	gpio(GPIO_MODE, (uint32_t)GPIOA, 5, OUTPUT);
+	//gpio_mode(GPIOA, 5, OUTPUT);
 	task_start(task2, 512);
 
 	for (int i = 0; i < 8; i++) {
 		gpio_dout(GPIOA, 5, !(i & 1));
 		delay(200);
 	}
-
-	return;
 }
 
+void task3(void);
 void task2(void)
 {
-	while (1)
-		delay(800);
+	delay(400);
+	task_start(task3, 1024);
+}
+
+void task3(void)
+{
+	int state = 0;
+	delay(2500);
+	while (1) {
+		gpio_dout(GPIOA, 5, state ^= 1);
+		delay(500);
+	}
 }
diff --git a/src/svc.c b/src/svc.c
new file mode 100644
index 0000000..4342a95
--- /dev/null
+++ b/src/svc.c
@@ -0,0 +1,53 @@
+/**
+ * @file svc.c
+ * An unused handler for SVC calls
+ * TODO: use SVC calls, possibly allowing for switch to unprivileged mode?
+ *
+ * Copyright (C) 2018 Clyne Sullivan
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <gpio.h>
+#include <clock.h>
+
+extern void gpio_svc(uint32_t *);
+
+void svc_handler(uint32_t *args)
+{
+	uint32_t svc_number = ((char *)args[6])[-2];
+
+	switch (svc_number) {
+	case 1:
+		gpio_svc(args);
+		break;
+	default:
+		break;
+	}
+}
+
+void SVC_Handler(void) {
+	uint32_t *args;
+
+	asm("\
+		tst lr, #4; \
+		ite eq; \
+		mrseq %0, msp; \
+		mrsne %0, psp; \
+	" : "=r" (args));
+
+	svc_handler(args);
+}
+