diff --git a/source/os/debug/include/board_devices.h b/source/os/debug/include/board_devices.h
index 16ace5b..78fc2e8 100644
--- a/source/os/debug/include/board_devices.h
+++ b/source/os/debug/include/board_devices.h
@@ -3,10 +3,14 @@
 #ifndef BOARD_DEVICES_H
 #define BOARD_DEVICES_H
 
+extern const struct driver pwm_4;
+extern const struct driver pwm_3;
+extern const struct driver pwm_2;
+extern const struct driver pwm_1;
 extern const struct driver uart_1;
-extern const struct driver led_3;
-extern const struct driver led_4;
-extern const struct driver led_5;
-extern const struct driver led_6;
+extern const struct driver gpio_c0;
+extern const struct driver gpio_c1;
+extern const struct driver gpio_c2;
+extern const struct driver gpio_c3;
 
 #endif /* BOARD_DEVICES_H */
diff --git a/source/os/debug/include/driver.h b/source/os/debug/include/driver.h
index ee82abf..14923d9 100644
--- a/source/os/debug/include/driver.h
+++ b/source/os/debug/include/driver.h
@@ -8,10 +8,13 @@
 #ifndef SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_
 #define SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_
 
+#define IOCTL_PWM_SET_DUTY_CYCLE	0
+
 enum driver_type {
 	DRIVER_TYPE_ADC,
 	DRIVER_TYPE_GPIO,
 	DRIVER_TYPE_I2C,
+	DRIVER_TYPE_PWM,
 	DRIVER_TYPE_RTC,
 	DRIVER_TYPE_SPI,
 	DRIVER_TYPE_UART
@@ -26,5 +29,6 @@ int open(const struct driver *driver);
 int close(const struct driver *driver);
 int read(const struct driver *driver, char *buffer, int len);
 int write(const struct driver *driver, const char *buffer, int len);
+int ioctl(const struct driver *driver, unsigned int cmd, const void *data);
 
 #endif /* SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_ */
diff --git a/source/os/debug/include/list.h b/source/os/debug/include/list.h
new file mode 100644
index 0000000..b87e3be
--- /dev/null
+++ b/source/os/debug/include/list.h
@@ -0,0 +1,24 @@
+/*
+ * list.h
+ *
+ *  Created on: Jul 27, 2016
+ *      Author: tkl
+ */
+
+#ifndef SOURCE_FIRMWARE_KERNEL_LIST_H_
+#define SOURCE_FIRMWARE_KERNEL_LIST_H_
+
+struct list_node {
+	struct list_node *next;
+	unsigned int data;
+};
+
+struct list {
+	struct list_node *front;
+	struct list_node *rear;
+};
+
+int list_init(struct list *head);
+int list_add(struct list *head, struct list_node *node);
+
+#endif /* SOURCE_FIRMWARE_KERNEL_LIST_H_ */
diff --git a/source/os/debug/include/shell.h b/source/os/debug/include/shell.h
new file mode 100644
index 0000000..81fd032
--- /dev/null
+++ b/source/os/debug/include/shell.h
@@ -0,0 +1,22 @@
+/*
+ * shell.h
+ *
+ *  Created on: Aug 1, 2016
+ *      Author: tkl
+ */
+
+#ifndef SOURCE_FIRMWARE_KERNEL_INTERFACE_SHELL_H_
+#define SOURCE_FIRMWARE_KERNEL_INTERFACE_SHELL_H_
+
+typedef void *(*command_callback)(const char*);
+
+struct command {
+	const char *command;
+	const command_callback command_callback;
+	struct list_node item;
+};
+
+int shell_init(const struct driver *shell_device);
+int shell_add_command(struct command *command);
+
+#endif /* SOURCE_FIRMWARE_KERNEL_INTERFACE_SHELL_H_ */
diff --git a/source/os/debug/libkosmos-arm-stm32f4-discovery-dbg.a b/source/os/debug/libkosmos-arm-stm32f4-discovery-dbg.a
index d285e6a..a8c73f0 100644
Binary files a/source/os/debug/libkosmos-arm-stm32f4-discovery-dbg.a and b/source/os/debug/libkosmos-arm-stm32f4-discovery-dbg.a differ
diff --git a/source/os/release/include/board_devices.h b/source/os/release/include/board_devices.h
index 16ace5b..78fc2e8 100644
--- a/source/os/release/include/board_devices.h
+++ b/source/os/release/include/board_devices.h
@@ -3,10 +3,14 @@
 #ifndef BOARD_DEVICES_H
 #define BOARD_DEVICES_H
 
+extern const struct driver pwm_4;
+extern const struct driver pwm_3;
+extern const struct driver pwm_2;
+extern const struct driver pwm_1;
 extern const struct driver uart_1;
-extern const struct driver led_3;
-extern const struct driver led_4;
-extern const struct driver led_5;
-extern const struct driver led_6;
+extern const struct driver gpio_c0;
+extern const struct driver gpio_c1;
+extern const struct driver gpio_c2;
+extern const struct driver gpio_c3;
 
 #endif /* BOARD_DEVICES_H */
diff --git a/source/os/release/include/driver.h b/source/os/release/include/driver.h
index ee82abf..14923d9 100644
--- a/source/os/release/include/driver.h
+++ b/source/os/release/include/driver.h
@@ -8,10 +8,13 @@
 #ifndef SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_
 #define SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_
 
+#define IOCTL_PWM_SET_DUTY_CYCLE	0
+
 enum driver_type {
 	DRIVER_TYPE_ADC,
 	DRIVER_TYPE_GPIO,
 	DRIVER_TYPE_I2C,
+	DRIVER_TYPE_PWM,
 	DRIVER_TYPE_RTC,
 	DRIVER_TYPE_SPI,
 	DRIVER_TYPE_UART
@@ -26,5 +29,6 @@ int open(const struct driver *driver);
 int close(const struct driver *driver);
 int read(const struct driver *driver, char *buffer, int len);
 int write(const struct driver *driver, const char *buffer, int len);
+int ioctl(const struct driver *driver, unsigned int cmd, const void *data);
 
 #endif /* SOURCE_FIRMWARE_KERNEL_DRIVER_INCLUDE_DRIVER_H_ */
diff --git a/source/os/release/libkosmos-arm-stm32f4-discovery.a b/source/os/release/libkosmos-arm-stm32f4-discovery.a
index 8455371..a8ef8be 100644
Binary files a/source/os/release/libkosmos-arm-stm32f4-discovery.a and b/source/os/release/libkosmos-arm-stm32f4-discovery.a differ