diff --git a/builder/sizes_test.go b/builder/sizes_test.go
index e96577d9b..f7ee7e1b2 100644
--- a/builder/sizes_test.go
+++ b/builder/sizes_test.go
@@ -42,9 +42,9 @@ func TestBinarySize(t *testing.T) {
 	// This is a small number of very diverse targets that we want to test.
 	tests := []sizeTest{
 		// microcontrollers
-		{"hifive1b", "examples/echo", 3680, 280, 0, 2252},
-		{"microbit", "examples/serial", 2694, 342, 8, 2248},
-		{"wioterminal", "examples/pininterrupt", 7074, 1510, 120, 7248},
+		{"hifive1b", "examples/echo", 3817, 299, 0, 2252},
+		{"microbit", "examples/serial", 2820, 356, 8, 2248},
+		{"wioterminal", "examples/pininterrupt", 8020, 1652, 132, 7480},
 
 		// TODO: also check wasm. Right now this is difficult, because
 		// wasm binaries are run through wasm-opt and therefore the
diff --git a/src/machine/machine_nrf52840_usb.go b/src/machine/machine_nrf52840_usb.go
index 4a2c5d5a7..0dc222b37 100644
--- a/src/machine/machine_nrf52840_usb.go
+++ b/src/machine/machine_nrf52840_usb.go
@@ -172,7 +172,7 @@ func handleUSBIRQ(interrupt.Interrupt) {
 		epDataStatus := nrf.USBD.EPDATASTATUS.Get()
 		nrf.USBD.EPDATASTATUS.Set(epDataStatus)
 		var i uint32
-		for i = 1; i < uint32(len(endPoints)); i++ {
+		for i = 1; i < NumberOfUSBEndpoints; i++ {
 			// Check if endpoint has a pending interrupt
 			inDataDone := epDataStatus&(nrf.USBD_EPDATASTATUS_EPIN1<<(i-1)) > 0
 			outDataDone := epDataStatus&(nrf.USBD_EPDATASTATUS_EPOUT1<<(i-1)) > 0
@@ -191,7 +191,7 @@ func handleUSBIRQ(interrupt.Interrupt) {
 	}
 
 	// ENDEPOUT[n] events
-	for i := 0; i < len(endPoints); i++ {
+	for i := 0; i < NumberOfUSBEndpoints; i++ {
 		if nrf.USBD.EVENTS_ENDEPOUT[i].Get() > 0 {
 			nrf.USBD.EVENTS_ENDEPOUT[i].Set(0)
 			buf := handleEndpointRx(uint32(i))
@@ -367,3 +367,19 @@ func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 
 	return b, nil
 }
+
+func (dev *USBDevice) SetStallEPIn(ep uint32) {
+	nrf.USBD.EPSTALL.Set(ep | nrf.USBD_EPSTALL_IO | nrf.USBD_EPSTALL_STALL)
+}
+
+func (dev *USBDevice) SetStallEPOut(ep uint32) {
+	nrf.USBD.EPSTALL.Set(ep | nrf.USBD_EPSTALL_STALL)
+}
+
+func (dev *USBDevice) ClearStallEPIn(ep uint32) {
+	nrf.USBD.EPSTALL.Set(ep | nrf.USBD_EPSTALL_IO)
+}
+
+func (dev *USBDevice) ClearStallEPOut(ep uint32) {
+	nrf.USBD.EPSTALL.Set(ep)
+}