fix(usb): implement endpoint stall for nRF52840.

Implement SetStallEPIn, SetStallEPOut, ClearStallEPIn, and ClearStallEPOut methods on the nRF52840 USBDevice struct using the hardware EPSTALL register to support MSC driver requirements. Also, correct the handleUSBIRQ loops to iterate over physical endpoint numbers rather than dynamic configuration entries to prevent missed or incorrectly routed endpoint interrupts.

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)
+}