initial commit

random/random.ino

@@ -0,0 +1,70 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+#include <stdint.h>
+#include <avr/interrupt.h>
+#include <avr/wdt.h>
+
+// data
+#define ALPHA_MAX 36
+char _itoa[ALPHA_MAX];
+
+void init_itoa(void) {
+  for (int i = 0; i < 10; i++)
+    _itoa[i] = (char)48 + i;
+  for (int i = 10; i < ALPHA_MAX; i++)
+    _itoa[i] = (char)55 + i;
+}
+
+// random
+#define CHAR_MAX 256
+volatile unsigned char _r_sample = 0;
+volatile char _r_new = 0;
+unsigned char _r = 0;
+const unsigned char _r_max = CHAR_MAX - (CHAR_MAX % ALPHA_MAX);
+
+ISR(WDT_vect) {
+  _r_sample = TCNT1L;
+  _r_new = 1;
+}
+
+void _r_init(void) {
+  cli();
+  MCUSR = 0;
+  WDTCSR |= _BV(WDCE) | _BV(WDE);
+  WDTCSR = _BV(WDIE);
+  sei();
+}
+
+char _r_rotl_one(const char v) {
+  int shift = 1;
+  if ((shift &= sizeof(v) * 8 - 1) == 0)
+    return v;
+  return (v << shift) | (v >> (sizeof(v) * 8 - shift));
+}
+
+char _r_char(void) {
+  char i = 0;
+  while (1) {
+    if (_r_new) {
+      _r_new = 0;
+      _r = _r_rotl_one(_r);
+      _r ^= _r_sample;
+      if (i++ > 7) {
+        if (_r < _r_max)
+          return _itoa[_r % ALPHA_MAX];
+        else
+          i = 0;
+      }
+    }
+  }
+}
+
+void setup(void) {
+  Serial.begin(115200);
+  _r_init();
+  init_itoa();
+}
+
+void loop(void) {
+  Serial.write(_r_char());
+}