'breathing' LED C example added

c/breathing_led.c

@@ -0,0 +1,100 @@
+#include <msp430g2553.h>
+
+const unsigned char curve[] = {
+    1,     1,     1,     1,     1,     1,     1,     1, 
+    1,     1,     1,     1,     1,     1,     1,     1, 
+    1,     1,     1,     2,     2,     2,     2,     2, 
+    2,     2,     3,     3,     3,     3,     3,     3, 
+    4,     4,     4,     4,     4,     5,     5,     5, 
+    5,     6,     6,     6,     6,     7,     7,     7, 
+    8,     8,     8,     8,     9,     9,     9,    10, 
+   10,    10,    11,    11,    11,    12,    12,    13, 
+   13,    13,    14,    14,    15,    15,    15,    16, 
+   16,    17,    17,    18,    18,    18,    19,    19, 
+   20,    20,    21,    21,    22,    22,    23,    23, 
+   24,    24,    25,    25,    26,    26,    27,    27, 
+   28,    29,    29,    30,    30,    31,    31,    32, 
+   33,    33,    34,    34,    35,    36,    36,    37, 
+   38,    38,    39,    39,    40,    41,    41,    42, 
+   43,    43,    44,    45,    46,    46,    47,    48, 
+   48,    49,    50,    50,    51,    52,    53,    53, 
+   54,    55,    56,    56,    57,    58,    59,    59, 
+   60,    61,    62,    62,    63,    64,    65,    66, 
+   66,    67,    68,    69,    70,    70,    71,    72, 
+   73,    74,    75,    75,    76,    77,    78,    79, 
+   80,    80,    81,    82,    83,    84,    85,    86, 
+   87,    87,    88,    89,    90,    91,    92,    93, 
+   94,    95,    95,    96,    97,    98,    99,   100, 
+  101,   102,   103,   104,   105,   106,   106,   107, 
+  108,   109,   110,   111,   112,   113,   114,   115, 
+  116,   117,   118,   119,   120,   121,   122,   122, 
+  123,   124,   125,   126,   127,   128,   129,   130, 
+  131,   132,   133,   134,   135,   136,   137,   138, 
+  139,   140,   141,   142,   143,   144,   145,   146, 
+  147,   148,   149,   150,   151,   152,   153,   154, 
+  155,   156
+};
+
+int pos = 0;   // Index to PWM's duty cycle table (= brightness)
+
+int main(void)
+{
+  // Stop watchdog
+  WDTCTL = WDTPW + WDTHOLD;
+
+  // Set clock to 1 MHz
+  DCOCTL= 0;
+  BCSCTL1= CALBC1_1MHZ;
+  DCOCTL= CALDCO_1MHZ;
+
+  // SMCLK = 1 MHz / 8 = 125 KHz (SLAU144E p.5-15)
+  BCSCTL2 |= DIVS_3;
+
+  // Make P1.6 (green led) an output. SLAU144E p.8-3
+  P1DIR |= BIT6;
+
+  // P1.6 = TA0.1 (timer A's output). SLAS694C p.41
+  P1SEL |= BIT6;              
+
+  // PWM period = 125 KHz / 625 = 200 Hz
+  TACCR0 = 625;
+
+  // Source Timer A from SMCLK (TASSEL_2), up mode (MC_1).
+  // Up mode counts up to TACCR0. SLAU144E p.12-20
+  TACTL = TASSEL_2 | MC_1;
+
+  // OUTMOD_7 = Reset/set output when the timer counts to TACCR1/TACCR0
+  // CCIE = Interrupt when timer counts to TACCR1
+  TACCTL1 = OUTMOD_7 | CCIE;
+
+  // Initial CCR1 (= brightness)
+  TACCR1 = 0;
+
+  // LPM0 (shut down the CPU) with interrupts enabled
+  __bis_SR_register(CPUOFF | GIE);
+
+  // Silly return to make gcc happy
+  return 0;
+}
+
+// This will be called when timer counts to TACCR1.
+void ta1_isr(void) __attribute__((interrupt(TIMER0_A1_VECTOR)));
+void ta1_isr(void)
+{
+  int new_ccr1 = 1;
+
+  // Clear interrupt flag
+  TACCTL1 &= ~CCIFG;
+
+  if (pos < 500) {
+    new_ccr1 = curve[pos++ >> 1];
+  } else if (pos < 1000) {
+    new_ccr1 = curve[(999 - pos++) >> 1];
+  } else {
+    pos = 0;
+  }
+  // Wait to set the new TACCR1 until TAR has gone past it, so that we
+  // don't get interrupted again in this period.
+  while (TAR <= new_ccr1) ;
+  TACCR1 = new_ccr1;
+}