stm32wl: STM32WL TRNG implementation in crypto/rand

src/crypto/rand/rand_baremetal.go

@@ -0,0 +1,36 @@
+//go:build stm32wle5
+// +build stm32wle5
+
+package rand
+
+import (
+	"machine"
+)
+
+func init() {
+	Reader = &reader{}
+}
+
+type reader struct {
+}
+
+func (r *reader) Read(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return
+	}
+
+	var randomByte uint32
+	for i := range b {
+		if i%4 == 0 {
+			randomByte, err = machine.GetRNG()
+			if err != nil {
+				return n, err
+			}
+		} else {
+			randomByte >>= 8
+		}
+		b[i] = byte(randomByte)
+	}
+
+	return len(b), nil
+}