stm32wl: Fix incomplete RNG initialisation

src/machine/machine.go

@@ -4,6 +4,8 @@ import "errors"
 
 var (
 	ErrTimeoutRNG         = errors.New("machine: RNG Timeout")
+	ErrClockRNG           = errors.New("machine: RNG Clock Error")
+	ErrSeedRNG            = errors.New("machine: RNG Seed Error")
 	ErrInvalidInputPin    = errors.New("machine: invalid input pin")
 	ErrInvalidOutputPin   = errors.New("machine: invalid output pin")
 	ErrInvalidClockPin    = errors.New("machine: invalid clock pin")

src/machine/machine_stm32_rng.go

@@ -15,6 +15,13 @@ func GetRNG() (uint32, error) {
 		rngInitDone = true
 	}
 
+	if stm32.RNG.SR.HasBits(stm32.RNG_SR_CECS) {
+		return 0, ErrClockRNG
+	}
+	if stm32.RNG.SR.HasBits(stm32.RNG_SR_SECS) {
+		return 0, ErrSeedRNG
+	}
+
 	cnt := RNG_MAX_READ_RETRIES
 	for !stm32.RNG.SR.HasBits(stm32.RNG_SR_DRDY) {
 		cnt--

src/machine/machine_stm32wlx.go

@@ -407,7 +407,12 @@ func (t *TIM) enableMainOutput() {
 
 func initRNG() {
 	stm32.RCC.AHB3ENR.SetBits(stm32.RCC_AHB3ENR_RNGEN)
-	stm32.RNG.CR.SetBits(stm32.RNG_CR_RNGEN)
+
+	// Enable RNG with config.A  (See RM0453 22.6.2)
+	stm32.RNG.CR.Set(0x40F00D40)   // RNG Config. A
+	stm32.RNG.HTCR.Set(0x17590ABC) // MAGIC NUMBER
+	stm32.RNG.HTCR.Set(0x0000AA74) // HTCR VALUE
+	stm32.RNG.CR.Set(0x00F00D4C)   // CONFIG A  + RNG_EN=1 + IE=1
 }
 
 //----------