Refactor Hardware RNG functions to esp/hwrand.h

As suggested by @foogod, thanks!

core/esp_hwrand.c

@@ -0,0 +1,27 @@
+/* Hardware Random Number Generator Functions
+ *
+ * For documentation, see http://esp8266-re.foogod.com/wiki/Random_Number_Generator
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2015 Angus Gratton
+ * BSD Licensed as described in the file LICENSE
+ */
+#include <esp/hwrand.h>
+#include <esp/wdev_regs.h>
+#include <string.h>
+
+/* Return a random 32-bit number */
+uint32_t hwrand(void)
+{
+    return WDEV.HWRNG;
+}
+
+/* Fill a variable size buffer with data from the Hardware RNG */
+void hwrand_fill(uint8_t *buf, size_t len)
+{
+    for(size_t i = 0; i < len; i+=4) {
+        uint32_t random = WDEV.HWRNG;
+        /* using memcpy here in case 'buf' is unaligned */
+        memcpy(buf + i, &random, (i+4 <= len) ? 4 : (len % 4));
+    }
+}

core/include/esp/hwrand.h

@@ -0,0 +1,22 @@
+/** esp/hwrand.h
+ *
+ * Hardware Random Number Generator functions.
+ *
+ * For documentation, see http://esp8266-re.foogod.com/wiki/Random_Number_Generator
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2015 Angus Gratton
+ * BSD Licensed as described in the file LICENSE
+ */
+#ifndef _ESP_RNG_H
+#define _ESP_RNG_H
+#include <stdint.h>
+#include <sys/types.h>
+
+/* Return a random 32-bit number */
+uint32_t hwrand(void);
+
+/* Fill a variable size buffer with data from the Hardware RNG */
+void hwrand_fill(uint8_t *buf, size_t len);
+
+#endif

extras/mbedtls/hardware_entropy.c

@@ -9,18 +9,13 @@
  * BSD Licensed as described in the file LICENSE
  */
 #include <mbedtls/entropy_poll.h>
-#include <esp/wdev_regs.h>
+#include <esp/hwrand.h>
-#include <string.h>
 
 int mbedtls_hardware_poll( void *data,
                            unsigned char *output, size_t len, size_t *olen )
 {
     (void)(data);
-    for(int i = 0; i < len; i+=4) {
+    hwrand_fill(output, len);
-        uint32_t random = WDEV.HWRNG;
-        /* using memcpy here in case output is unaligned */
-        memcpy(output + i, &random, (i+4 <= len) ? 4 : (len % 4));
-    }
     if(olen)
         *olen = len;
     return 0;