Implemented irregular ticks.

With two /8 dividers we get 512 interrupts per second. By counting 16
of these we get a 30ms interval to energise the coil for a tick.
We add a random number up to 15 additional 30ms intervals to offset the
actual time of the tick.

diff --git a/main.c b/main.c
index 155a72cf501d0cbbee3a32daf3cbdb95bac6e2e4..85ce41f5cfebf222ee1686931d9dabfae17c743c 100644 (file)
--- a/main.c
+++ b/main.c
@@ -1,21 +1,27 @@
 #include <msp430.h>
 #include <legacymsp430.h>
+#include <stdint.h>
+#include <stdlib.h>
 
 #define LED0 BIT0 /* P1.0 */
+#define CLKP BIT1 /* P1.1 */
+#define CLKN BIT2 /* P1.2 */
 
 static void
 init_leds(void)
 {
-    P1DIR |= LED0; /* set P1.0 as output */
-    P1OUT |= LED0; /* set P1.0 low */
-
-    /* set timer A to use the aux clock in UP mode with ACLK/8 divider */
-    TACTL = TASSEL_1 | MC_1 | ID_3;
+    //P1DIR |= LED0 | CLKP | CLKN; /* set P1.0,P1.1,P1.2 as output */
+    //P1OUT |= LED0 | CLKP | CLKN; /* set P1.0,P1.1,P1.2 low */
+    P1DIR = 0xff; /* set P1.* to output for reduced power consumption */
+    P1OUT = LED0 | CLKP | CLKN;
+    
     /* set the counter to match on 511 which is 1s for 32kHz/8/8 (timer
      * re-divides the interrupt clock by 8 */
-    TACCR0 = 511;
+    TACCR0 = 15; /* count 16 intervals for 31ms delay */
     /* enable the clock interrupt mode for TACCR0 match */
     TACCTL0 = CCIE;
+    /* set timer A to use the aux clock in UP mode with ACLK/8 divider */
+    TACTL = TASSEL_1 | MC_1 | ID_3; /* and starts the timer */
 }
 
 int
@@ -28,6 +34,7 @@ main(void)
     BCSCTL1 |= DIVA_3; /* ACLK/8 */
     BCSCTL3 |= XCAP_3; /* enable 12.5pF internal capacitance */
     
+    srand(0xf00d);
     init_leds();
 
     /* enable global interrupts */
@@ -40,10 +47,41 @@ main(void)
     }
 }
 
+enum State {State_Wait, State_Delay, State_Driving};
+enum State state = State_Wait;
+static uint8_t count = 0;
+static int8_t offset = 0;
+static uint8_t pin_pos = CLKP;
+static uint8_t pin_neg = CLKN;
+
 interrupt(TIMER0_A0_VECTOR)
 TIMERA0_ISR(void)
 {
-    /* clear the interrupt flag and toggle LED */
+    /* clear the interrupt flag */
     TACCTL0 &= ~CCIFG;
-    P1OUT ^= LED0;
+    ++count;
+
+    /* if driving the stepper coil, stop after 32ms (1 interrupt) */
+    if (state == State_Driving) {
+        state = State_Wait;
+        P1OUT &= ~(CLKP | CLKN | LED0);
+    }
+    
+    if (count == 32) {
+        count = 0;
+        offset = 1 + (rand() & 0x0f);
+        state = State_Delay;
+    }
+    if (state == State_Delay) {
+        --offset;
+        if (offset == 0) {
+            state = State_Driving;
+            P1OUT |= pin_pos | LED0;
+            P1OUT &= ~pin_neg;
+            /* swap the pins for the next tick */
+            uint8_t t = pin_pos;
+            pin_pos = pin_neg;
+            pin_neg = t;
+        }
+    }
 }