cpu/stm32f4: added random number generator driver

cpu/stm32f4/periph/random.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2014 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @ingroup     cpu_stm32f4
+ * @{
+ *
+ * @file
+ * @brief       Low-level random number generator driver implementation
+ *
+ * @author      Hauke Petersen <mail@haukepetersen.de>
+ *
+ * @}
+ */
+
+#include "cpu.h"
+#include "periph/random.h"
+#include "periph_conf.h"
+
+/* ignore file in case no RNG device is defined */
+#if RANDOM_NUMOF
+
+void random_init(void)
+{
+    random_poweron();
+}
+
+int random_read(char *buf, unsigned int num)
+{
+    uint32_t tmp;
+    int count = 0;
+
+    while (count < num) {
+        /* wait for random data to be ready to read */
+        while (!(RNG->SR & RNG_SR_DRDY));
+        /* read next 4 bytes */
+        tmp = RNG->DR;
+        /* copy data into result vector */
+        for (int i = 0; i < 4 && count < num; i++) {
+            buf[count++] = (char)tmp;
+            tmp = tmp >> 8;
+        }
+    }
+
+    return count;
+}
+
+void random_poweron(void)
+{
+    RCC->AHB2ENR |= RCC_AHB2ENR_RNGEN;
+    RNG->CR = RNG_CR_RNGEN;
+}
+
+void random_poweroff(void)
+{
+    RNG->CR = 0;
+    RCC->AHB2ENR &= ~RCC_AHB2ENR_RNGEN;
+}
+
+#endif /* RANDOM_NUMOF */