fix hangs due to stale rng status (#195)

Makefile.include

@@ -65,6 +65,12 @@ else
 CFLAGS += -DMEMORY_PROTECT=1
 endif
 
+ifeq ($(DEBUG_RNG), 1)
+CFLAGS += -DDEBUG_RNG=1
+else
+CFLAGS += -DDEBUG_RNG=0
+endif
+
 LDFLAGS  += --static \
             -Wl,--start-group \
             -lc \

firmware/fsm.c

@@ -330,12 +330,14 @@ void fsm_msgWipeDevice(WipeDevice *msg)
 
 void fsm_msgGetEntropy(GetEntropy *msg)
 {
+#if !DEBUG_RNG
 	layoutDialogSwipe(&bmp_icon_question, _("Cancel"), _("Confirm"), NULL, _("Do you really want to"), _("send entropy?"), NULL, NULL, NULL, NULL);
 	if (!protectButton(ButtonRequestType_ButtonRequest_ProtectCall, false)) {
 		fsm_sendFailure(FailureType_Failure_ActionCancelled, NULL);
 		layoutHome();
 		return;
 	}
+#endif
 	RESP_INIT(Entropy);
 	uint32_t len = msg->size;
 	if (len > 1024) {

rng.c

@@ -27,7 +27,7 @@ uint32_t random32(void)
 {
 	static uint32_t last = 0, new = 0;
 	while (new == last) {
-		if (((RNG_SR & (RNG_SR_SEIS | RNG_SR_CEIS)) == 0) && ((RNG_SR & RNG_SR_DRDY) > 0)) {
+		if ((RNG_SR & (RNG_SR_SECS | RNG_SR_CECS | RNG_SR_DRDY)) == RNG_SR_DRDY) {
 			new = RNG_DR;
 		}
 	}

setup.c

@@ -42,7 +42,7 @@ void setup(void)
 
 	// enable RNG
 	rcc_periph_clock_enable(RCC_RNG);
-	RNG_CR |= RNG_CR_IE | RNG_CR_RNGEN;
+	RNG_CR |= RNG_CR_RNGEN;
 	// to be extra careful and heed the STM32F205xx Reference manual, Section 20.3.1
 	// we don't use the first random number generated after setting the RNGEN bit in setup
 	random32();
@@ -73,6 +73,9 @@ void setup(void)
 
 void setupApp(void)
 {
+	// for completeness, disable RNG peripheral interrupts for old bootloaders that had
+	// enabled them in RNG control register (the RNG interrupt was never enabled in the NVIC)
+	RNG_CR &= ~RNG_CR_IE;
 	// the static variables in random32 are separate between the bootloader and firmware.
 	// therefore, they need to be initialized here so that we can be sure to avoid dupes.
 	// this is to try to comply with STM32F205xx Reference manual - Section 20.3.1: