This change provides an option to add /dev/urandom to all architectures. The pseudo-random algorithm I choose strikes an arguably-good balance between being "random" and small/fast enough for 8/16 bit MCUs. It’s the well-documented xorshift128 algorithm. It has an internal state of 128 bits that can be [re-]seeded with a write.

include/nuttx/fs/fs.h

@@ -1013,6 +1013,16 @@ int fdesc_poll(int fd, FAR struct pollfd *fds, bool setup);
 
 void devnull_register(void);
 
+/****************************************************************************
+ * Name: devurandom_register
+ *
+ * Description:
+ *   Register /dev/urandom
+ *
+ ****************************************************************************/
+
+void devurandom_register(void);
+
 /****************************************************************************
  * Name: devcrypto_register
  *