Initial commit: Code from January 2011

Working implementation of SLAA338 and an LCG, with a very simple test.

Makefile

@@ -0,0 +1,13 @@
+CC = msp430-gcc
+CFLAGS = -Wall -Wno-main -Os -g -mmcu=msp430x2211
+
+OBJS=rand.o
+
+all: $(OBJS)
+	$(CC) $(CFLAGS) -o main.elf $(OBJS)
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $<
+
+clean:
+	rm -f main.elf $(OBJS)

rand.c

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+#include <io.h>
+
+/**
+ * Random number generator.
+ *
+ * NOTE: This affects Timer A.
+ *
+ * Algorithm from TI SLAA338:
+ * http://www.ti.com/sc/docs/psheets/abstract/apps/slaa338.htm
+ *
+ * @return 16 random bits generated from a hardware source.
+ */
+unsigned int rand() {
+	int i, j;
+	unsigned int result = 0;
+
+	TACCTL0 = CAP | CM_1 | CCIS_1;            // Capture mode, positive edge
+	TACTL = TASSEL_2 | MC_2;                  // SMCLK, continuous up
+
+	for (i = 0; i < 16; i++) {
+		unsigned int ones = 0;
+
+		for (j = 0; j < 5; j++) {
+			while (!(CCIFG & TACCTL0));       // Wait for interrupt
+
+			TACCTL0 &= ~CCIFG;                // Clear interrupt
+
+			if (1 & TACCR0)                   // If LSB set, count it
+				ones++;
+		}
+
+		result >>= 1;                         // Save previous bits
+
+		if (ones >= 3)                        // Best out of 5
+			result |= 0x8000;                 // Set MSB
+	}
+
+	return result;
+}
+
+#define M 49381                               // Multiplier
+#define I 8643                                // Increment
+
+/**
+ * Pseudo-random number generator.
+ *
+ * 16-bit linear congruential generator.
+ * NOTE: Only treat the upper byte of the return value as random.
+ *
+ * @param state Previous state of the generator.
+ * @return Next state of the generator.
+ */
+unsigned int prand(unsigned int state) {
+	return (M * state + I);                   // Generate the next state of the LCG
+}
+
+/*
+ * Test:
+ */
+
+#define TIMES 32
+
+/**
+ * Red light on   => Waiting for rand() to return
+ * Green light on => Done
+ */
+void main() {
+	volatile unsigned int result[TIMES];
+	unsigned int s;
+	int i;
+
+	P1DIR |= BIT0 | BIT6;
+	P1OUT |= BIT0;                            // R
+	P1OUT &= ~BIT6;                           // !G
+
+	s = rand();
+	result[0] = s;
+
+	P1OUT &= ~BIT0;                           // !R
+
+	for (i = 1; i < TIMES; i++) {
+		s = prand(s);
+		result[i] = s;
+	}
+
+	P1OUT |= BIT6;                            // G
+
+	asm("mov %0, r8" : : "r" (&result));      // Manually check TIMES words starting at address in r8
+}