Started following some tutorial on att85 usi. Downloaded example code from make avr book.

Make AVR Examples/Chapter04_Bit-Twiddling/cylonEyes_8LFSR/8LFSR.c

@@ -0,0 +1,70 @@
+// ------- Preamble -------- //
+#include <avr/io.h>
+#include <util/delay.h>
+
+#define DELAY     100                                            /* ms */
+
+static inline uint8_t LFSR8_step(uint8_t random);
+
+int main(void) {
+
+  // -------- Inits --------- //
+
+  DDRB = 0xff;                                   /* output on all LEDs */
+  uint8_t random = 1;              /* can't init to 0, any other is ok */
+
+  // ------ Event loop ------ //
+  while (1) {
+
+                                                 /* Display and output */
+    random = LFSR8_step(random);
+    PORTB = random;
+    _delay_ms(DELAY);
+
+  }                                                  /* End event loop */
+  return 0;
+}
+
+
+// ----------------- LFSR Routines ---------------- //
+
+inline uint8_t LFSR8_step(uint8_t random) {
+  /*
+     Takes an 8-bit number, takes one step in a () LFSR.
+     [3, 4, 5, 7] is the set of taps for 8-bits that goes through
+     the whole cycle before repeating.
+
+     If you're really serious about randomness, you'll want a different
+     algorithm.  In fact, this is a great demo of how "predictable"
+     the "pseudo-random" sequence is.
+
+     Note that this is not a very efficient way to code this up,
+     but it's meant mostly for teaching and is plenty fast
+     because the compiler does an OK job with it.
+   */
+  uint8_t tap1, tap2, tap3, tap4;
+  uint8_t newBit;
+  tap1 = 1 & (random >> 3);
+  tap2 = 1 & (random >> 4);
+  tap3 = 1 & (random >> 5);
+  tap4 = 1 & (random >> 7);
+
+  newBit = tap1 ^ tap2 ^ tap3 ^ tap4;
+  random = ((random << 1) | newBit);
+  return (random);
+}
+
+
+inline uint16_t LFSR16(uint16_t random) {
+  // 3, 12, 14, 15 are the maximal taps for 16 bits.
+  uint16_t tap1, tap2, tap3, tap4;
+  uint16_t newBit;
+  tap1 = 1 & (random >> 3);
+  tap2 = 1 & (random >> 12);
+  tap3 = 1 & (random >> 14);
+  tap4 = 1 & (random >> 15);
+
+  newBit = tap1 ^ tap2 ^ tap3 ^ tap4;
+  random = ((random << 1) | newBit);
+  return (random);
+}