1 files changed, 69 insertions, 0 deletions
diff --git a/bsps/shared/dev/getentropy/getentropy-cpucounter.c b/bsps/shared/dev/getentropy/getentropy-cpucounter.c
new file mode 100644
index 0000000000..8ef05df85c
--- /dev/null
+++ b/bsps/shared/dev/getentropy/getentropy-cpucounter.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2017 embedded brains GmbH.  All rights reserved.
+ *
+ *  embedded brains GmbH
+ *  Dornierstr. 4
+ *  82178 Puchheim
+ *  Germany
+ *  <rtems@embedded-brains.de>
+ *
+ * The license and distribution terms for this file may be
+ * found in the file LICENSE in this distribution or at
+ * http://www.rtems.org/license/LICENSE.
+ */
+
+/*
+ * ATTENTION: THIS IS A VERY LIMITED ENTROPY SOURCE.
+ *
+ * This implementation uses a time-based value for it's entropy. The only thing
+ * that makes it random are interrupts from external sources. Don't use it if
+ * you need for example a strong crypto.
+ */
+
+#include <sys/param.h>
+#include <unistd.h>
+#include <string.h>
+#include <rtems/bsd.h>
+#include <rtems/counter.h>
+#include <rtems/sysinit.h>
+
+static uint32_t state;
+
+int getentropy(void *ptr, size_t n)
+{
+  uint8_t *dest = ptr;
+
+  state ^= rtems_counter_read();
+  state *= 25169206;
+  state += 1679610226;
+
+  while (n > 0) {
+    size_t m;
+
+    m = MIN(n, sizeof(state));
+    memcpy(dest, &state, m);
+    n -= m;
+    dest += m;
+    state *= 85236167;
+    state += 30557471;
+  }
+
+  return 0;
+}
+
+static void getentropy_init(void)
+{
+  struct bintime bt;
+
+  rtems_bsd_bintime(&bt);
+  state = (uint32_t) bt.frac;
+  state ^= (uint32_t) (bt.frac >> 32);
+  state ^= (uint32_t) bt.sec;
+  state ^= (uint32_t) (bt.sec >> 32);
+}
+
+RTEMS_SYSINIT_ITEM(
+  getentropy_init,
+  RTEMS_SYSINIT_DEVICE_DRIVERS,
+  RTEMS_SYSINIT_ORDER_LAST
+);