diff --git a/lib/contiki-core/sys/autostart.c b/lib/contiki-core/sys/autostart.c
index 19aed8add..9329a9f52 100644
--- a/lib/contiki-core/sys/autostart.c
+++ b/lib/contiki-core/sys/autostart.c
@@ -57,7 +57,7 @@ autostart_start(struct process * const processes[])
   int i;
 
   for(i = 0; processes[i] != NULL; ++i) {
-    process_start(processes[i], NULL);
+    process_start(processes[i]);
     PRINTF("autostart_start: starting process '%s'\n", processes[i]->name);
   }
 }
diff --git a/lib/contiki-core/sys/ctimer.c b/lib/contiki-core/sys/ctimer.c
index f74fd9046..ff5be8da0 100644
--- a/lib/contiki-core/sys/ctimer.c
+++ b/lib/contiki-core/sys/ctimer.c
@@ -93,7 +93,7 @@ ctimer_init(void)
 {
   initialized = 0;
   list_init(ctimer_list);
-  process_start(&ctimer_process, NULL);
+  process_start(&ctimer_process);
 }
 /*---------------------------------------------------------------------------*/
 void
diff --git a/lib/contiki-core/sys/process.c b/lib/contiki-core/sys/process.c
index 25bb4f8c6..79b765cb8 100644
--- a/lib/contiki-core/sys/process.c
+++ b/lib/contiki-core/sys/process.c
@@ -97,7 +97,7 @@ process_alloc_event(void)
 }
 /*---------------------------------------------------------------------------*/
 void
-process_start(struct process *p, process_data_t data)
+process_start(struct process *p)
 {
   struct process *q;
 
@@ -118,7 +118,7 @@ process_start(struct process *p, process_data_t data)
   PRINTF("process: starting '%s'\n", PROCESS_NAME_STRING(p));
 
   /* Post a synchronous initialization event to the process. */
-  process_post_synch(p, PROCESS_EVENT_INIT, data);
+  process_post_synch(p, PROCESS_EVENT_INIT, NULL);
 }
 /*---------------------------------------------------------------------------*/
 static void
diff --git a/lib/contiki-core/sys/process.h b/lib/contiki-core/sys/process.h
index 76d336525..aa4318ad6 100644
--- a/lib/contiki-core/sys/process.h
+++ b/lib/contiki-core/sys/process.h
@@ -335,12 +335,8 @@ struct process {
  * Start a process.
  *
  * \param p A pointer to a process structure.
- *
- * \param data An argument pointer that can be passed to the new
- * process
- *
  */
-CCIF void process_start(struct process *p, process_data_t data);
+CCIF void process_start(struct process *p);
 
 /**
  * Post an asynchronous event.
diff --git a/lib/contiki-core/sys/procinit.c b/lib/contiki-core/sys/procinit.c
index ca09fc3dd..96bf82876 100644
--- a/lib/contiki-core/sys/procinit.c
+++ b/lib/contiki-core/sys/procinit.c
@@ -43,7 +43,7 @@ procinit_init(void)
   int i;
 
   for(i = 0; procinit[i] != NULL; ++i) {
-    process_start((struct process *)procinit[i], NULL);
+    process_start((struct process *)procinit[i]);
   }
 }
 /*---------------------------------------------------------------------------*/
diff --git a/lib/contiki-core/sys/subprocess.h b/lib/contiki-core/sys/subprocess.h
index 1281aa6cc..317845c62 100644
--- a/lib/contiki-core/sys/subprocess.h
+++ b/lib/contiki-core/sys/subprocess.h
@@ -57,7 +57,7 @@
 {									\
   static struct process subprocess_subprocess = {NULL, strname};	\
   subprocess_subprocess.thread = PROCESS_CURRENT()->thread;		\
-  process_start(&subprocess_subprocess, NULL);				\
+  process_start(&subprocess_subprocess);				\
   PT_INIT(&subprocess_subprocess.pt);					\
   LC_SET(subprocess_subprocess.pt.lc);					\
   if(PROCESS_CURRENT() == &subprocess_subprocess) {
diff --git a/lib/pbio/drv/bluetooth/bluetooth_btstack_run_loop_contiki.c b/lib/pbio/drv/bluetooth/bluetooth_btstack_run_loop_contiki.c
index dbbb53efe..b8f634184 100644
--- a/lib/pbio/drv/bluetooth/bluetooth_btstack_run_loop_contiki.c
+++ b/lib/pbio/drv/bluetooth/bluetooth_btstack_run_loop_contiki.c
@@ -37,7 +37,7 @@ static void schedule_timer(void) {
 }
 
 static void btstack_run_loop_contiki_init(void) {
-    process_start(&btstack_run_loop_contiki_process, NULL);
+    process_start(&btstack_run_loop_contiki_process);
 }
 
 static void btstack_run_loop_contiki_add_data_source(btstack_data_source_t *ds) {
diff --git a/lib/pbio/drv/bluetooth/bluetooth_stm32_bluenrg.c b/lib/pbio/drv/bluetooth/bluetooth_stm32_bluenrg.c
index fab5e5afc..1a019e383 100644
--- a/lib/pbio/drv/bluetooth/bluetooth_stm32_bluenrg.c
+++ b/lib/pbio/drv/bluetooth/bluetooth_stm32_bluenrg.c
@@ -179,7 +179,7 @@ void pbdrv_bluetooth_init(void) {
 
 void pbdrv_bluetooth_power_on(bool on) {
     if (on) {
-        process_start(&pbdrv_bluetooth_spi_process, NULL);
+        process_start(&pbdrv_bluetooth_spi_process);
     } else {
         // REVISIT: should probably gracefully shutdown in case we are in the
         // middle of something
diff --git a/lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c b/lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c
index 865f9baf4..d49e99bd4 100644
--- a/lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c
+++ b/lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c
@@ -218,7 +218,7 @@ void pbdrv_bluetooth_init(void) {
 
 void pbdrv_bluetooth_power_on(bool on) {
     if (on) {
-        process_start(&pbdrv_bluetooth_spi_process, NULL);
+        process_start(&pbdrv_bluetooth_spi_process);
     } else {
         // REVISIT: should probably gracefully shutdown in case we are in the
         // middle of something
diff --git a/lib/pbio/drv/core.c b/lib/pbio/drv/core.c
index 21c0aa070..60e446cd4 100644
--- a/lib/pbio/drv/core.c
+++ b/lib/pbio/drv/core.c
@@ -21,7 +21,7 @@ uint32_t pbdrv_init_busy_count;
 void pbdrv_init(void) {
     clock_init();
     process_init();
-    process_start(&etimer_process, NULL);
+    process_start(&etimer_process);
     pbdrv_battery_init();
     pbdrv_bluetooth_init();
     pbdrv_counter_init();
diff --git a/lib/pbio/drv/ioport/ioport_lpf2.c b/lib/pbio/drv/ioport/ioport_lpf2.c
index e77a668aa..51452029c 100644
--- a/lib/pbio/drv/ioport/ioport_lpf2.c
+++ b/lib/pbio/drv/ioport/ioport_lpf2.c
@@ -136,7 +136,7 @@ PROCESS(pbdrv_ioport_lpf2_process, "I/O port");
 static ioport_dev_t ioport_devs[PBDRV_CONFIG_IOPORT_LPF2_NUM_PORTS];
 
 void pbdrv_ioport_lpf2_init(void) {
-    process_start(&pbdrv_ioport_lpf2_process, NULL);
+    process_start(&pbdrv_ioport_lpf2_process);
 }
 
 void pbdrv_ioport_lpf2_shutdown(void) {
diff --git a/lib/pbio/drv/pwm/pwm_tlc5955_stm32.c b/lib/pbio/drv/pwm/pwm_tlc5955_stm32.c
index f524efba3..3121fdec0 100644
--- a/lib/pbio/drv/pwm/pwm_tlc5955_stm32.c
+++ b/lib/pbio/drv/pwm/pwm_tlc5955_stm32.c
@@ -243,7 +243,7 @@ void pbdrv_pwm_tlc5955_stm32_init(pbdrv_pwm_dev_t *devs) {
         pbdrv_init_busy_up();
     }
 
-    process_start(&pwm_tlc5955_stm32, NULL);
+    process_start(&pwm_tlc5955_stm32);
 }
 
 // toggles LAT signal on and off to latch data in shift register
diff --git a/lib/pbio/src/light/animation.c b/lib/pbio/src/light/animation.c
index 07cfbdcfc..d65a427d7 100644
--- a/lib/pbio/src/light/animation.c
+++ b/lib/pbio/src/light/animation.c
@@ -49,7 +49,7 @@ void pbio_light_animation_start(pbio_light_animation_t *animation) {
     animation->next_animation = pbio_light_animation_list_head;
     pbio_light_animation_list_head = animation;
 
-    process_start(&pbio_light_animation_process, NULL);
+    process_start(&pbio_light_animation_process);
     // HACK: init timer since we don't call etimer_set()
     timer_set(&animation->timer.timer, 0);
     // fake a timer event to load the first cell and start the timer
diff --git a/lib/pbio/sys/bluetooth.c b/lib/pbio/sys/bluetooth.c
index e78bdab42..f3422290f 100644
--- a/lib/pbio/sys/bluetooth.c
+++ b/lib/pbio/sys/bluetooth.c
@@ -51,7 +51,7 @@ void pbsys_bluetooth_init(void) {
 
     lwrb_init(&uart_tx_ring, uart_tx_buf, PBIO_ARRAY_SIZE(uart_tx_buf));
     lwrb_init(&uart_rx_ring, uart_rx_buf, PBIO_ARRAY_SIZE(uart_rx_buf));
-    process_start(&pbsys_bluetooth_process, NULL);
+    process_start(&pbsys_bluetooth_process);
 }
 
 static void on_event(void) {
diff --git a/lib/pbio/test/drv/bluetooth.c b/lib/pbio/test/drv/bluetooth.c
index 10fcfb97e..7e9c62fcc 100644
--- a/lib/pbio/test/drv/bluetooth.c
+++ b/lib/pbio/test/drv/bluetooth.c
@@ -452,8 +452,8 @@ PROCESS_THREAD(test_uart_send_process, ev, data) {
 
 static int test_uart_block_init(const btstack_uart_config_t *uart_config) {
     log_debug("%s", __func__);
-    process_start(&test_uart_receive_process, NULL);
-    process_start(&test_uart_send_process, NULL);
+    process_start(&test_uart_receive_process);
+    process_start(&test_uart_send_process);
     return 0;
 }
 
diff --git a/lib/pbio/test/src/servo.c b/lib/pbio/test/src/servo.c
index 9fd74381f..64302f060 100644
--- a/lib/pbio/test/src/servo.c
+++ b/lib/pbio/test/src/servo.c
@@ -85,7 +85,7 @@ static PT_THREAD(test_servo_run_func(struct pt *pt, const char *name, pbio_error
 
     PT_BEGIN(pt);
 
-    process_start(&pbio_motor_process, NULL);
+    process_start(&pbio_motor_process);
     tt_want(process_is_running(&pbio_motor_process));
 
     tt_uint_op(pbio_motor_process_get_servo(PBIO_PORT_ID_A, &servo), ==, PBIO_SUCCESS);
diff --git a/lib/pbio/test/src/uartdev.c b/lib/pbio/test/src/uartdev.c
index 9f4ee4f32..e377bf1d5 100644
--- a/lib/pbio/test/src/uartdev.c
+++ b/lib/pbio/test/src/uartdev.c
@@ -221,7 +221,7 @@ static PT_THREAD(test_boost_color_distance_sensor(struct pt *pt)) {
 
     PT_BEGIN(pt);
 
-    process_start(&pbio_uartdev_process, NULL);
+    process_start(&pbio_uartdev_process);
 
     // starting baud rate of hub
     PT_WAIT_UNTIL(pt, {
@@ -507,7 +507,7 @@ static PT_THREAD(test_boost_interactive_motor(struct pt *pt)) {
 
     PT_BEGIN(pt);
 
-    process_start(&pbio_uartdev_process, NULL);
+    process_start(&pbio_uartdev_process);
 
     // starting baud rate of hub
     PT_WAIT_UNTIL(pt, {
@@ -695,7 +695,7 @@ static PT_THREAD(test_technic_large_motor(struct pt *pt)) {
 
     PT_BEGIN(pt);
 
-    process_start(&pbio_uartdev_process, NULL);
+    process_start(&pbio_uartdev_process);
 
     // baud rate for sync messages
     PT_WAIT_UNTIL(pt, {
@@ -903,7 +903,7 @@ static PT_THREAD(test_technic_xl_motor(struct pt *pt)) {
 
     PT_BEGIN(pt);
 
-    process_start(&pbio_uartdev_process, NULL);
+    process_start(&pbio_uartdev_process);
 
     // baud rate for sync messages
     PT_WAIT_UNTIL(pt, {
diff --git a/lib/pbio/test/sys/status.c b/lib/pbio/test/sys/status.c
index 1416d7ba0..19ea78332 100644
--- a/lib/pbio/test/sys/status.c
+++ b/lib/pbio/test/sys/status.c
@@ -32,7 +32,7 @@ PROCESS_THREAD(status_test_process, ev, data) {
 static PT_THREAD(test_status(struct pt *pt)) {
     PT_BEGIN(pt);
 
-    process_start(&status_test_process, NULL);
+    process_start(&status_test_process);
 
     // use the last valid flag for edge case
     static const pbio_pybricks_status_t test_flag = NUM_PBIO_PYBRICKS_STATUS - 1;