LED Blink Using Timer of Cortex-M3

Click here to read LED Blink Using Cortex-M3.
The LPC1343 development board which we will use in this tutorial has two Led's, one green and another is Blue, the following program will toggle the Led's after 1 second, Blue Led state is controlled using 16-bit timer interrupt while Green Led state is controlled using millis() function, as done in Led Blink post.

 #include "config.h"  
 #include "lpc13xx_gpio.h"  
 boolean blueLedState = TRUE;  
 boolean greenLedState = TRUE;  
 int main(void)  
 {  
  u32_t time = millis();  
  InitializeSystem();          // Initialize System Clock and SysTick Interrupt  
  // Power On the GPIO Clock  
  SYSCON_AHBPeriphClockCmd(SYSCON_AHBPeriph_GPIO, ENABLE);  
  // Set Direction as Output  
  GPIO_SetDir(PORT1, GreenLED, 1);  
  GPIO_SetDir(PORT1, BlueLED, 1);  
  // Supply Power to 16-bit Timer Module-0  
  SYSCON_AHBPeriphClockCmd(SYSCON_AHBPeriph_CT16B0, ENABLE);  
  // Following Values of Match Register and Prescale Register,  
  // is used to produce interrupt @ 1 millisecond.  
  // Match Register Value  
  LPC_TMR16B0->MR0 = 720-1;  
  // LPC_TMR16B0->PC will count from 0-100 to increment TC by One  
  LPC_TMR16B0->PR = 100;  
  // Generate Interrupt when Match Register 0 = TC  
  // Clear TC contents  
  LPC_TMR16B0->MCR = 0x03;  
  // Reset Counter  
  LPC_TMR16B0->TCR |= (1<<1);  
  LPC_TMR16B0->TCR &= ~(1<<1);  
  // Enable Timer-0 Interrupt  
  NVIC_EnableIRQ(TIMER_16_0_IRQn);  
  // Start Timer  
  LPC_TMR16B0->TCR |= (1<<0);  
  while(1)  
  {  
   if(millis() - time > 1000 )  
   {  
    time = millis();  
    // Toggle Green Led State  
    if(greenLedState == TRUE)  
    {  
     greenLedState = FALSE;  
     // Set GPIO pins State High  
     GPIO_SetBits(PORT1, GreenLED);  
    }  
    else  
    {  
     greenLedState = TRUE;  
     // Set GPIO pins State Low  
     GPIO_ResetBits(PORT1, GreenLED);  
    }  
   }  
  }  
 }  
 //===================================================//  
 // Timer-0 16 Bit Interrupt Handler  
 // Toggles Blue Led State, after 1 second  
 // This is approximate.  
 //===================================================//  
 void TIMER16_0_IRQHandler(void)  
 {  
  static u32_t count = 0;  
  count++;  
  if(count % 1000 == 999)    // Change Led Status after 1 second  
  {  
   // Toggle Blue Led State  
   if(blueLedState == TRUE)  
   {  
    blueLedState = FALSE;  
    // Set GPIO pins State High  
    GPIO_SetBits(PORT1, BlueLED);  
   }  
   else  
   {  
    blueLedState = TRUE;  
    // Set GPIO pins State Low  
    GPIO_ResetBits(PORT1, BlueLED);  
   }  
  }  
  LPC_TMR16B0->IR = 0x01;    // Clear Interrupt  
 }

Now let us understand the program, step by step.
// Supply Power to 16-bit Timer Module-0
SYSCON_AHBPeriphClockCmd(SYSCON_AHBPeriph_CT16B0, ENABLE);
Clock to all peripherals is disabled by default, except for GPIO's, so by using the above line, clock is supplied to Timer-0 module of LPC1343.

// Following Values of Match Register and Prescale Register,
// is used to produce interrupt @ 1 millisecond.
// Match Register Value
LPC_TMR16B0->MR0 = 720-1;
// LPC_TMR16B0->PC will count from 0-100 to increment TC by One
LPC_TMR16B0->PR = 100;The above two statements configure the timer to generate interrupt at 1 millisecond rate.
(Note: The above configuration of timer is not accurate)

// Generate Interrupt when Match Register 0 = TC
// Clear TC contents
LPC_TMR16B0->MCR = 0x03;The above line generate timer interrupt, upon match with Match Register-0 value, which we have set to 719 in the above lines.

// Reset Counter
LPC_TMR16B0->TCR |= (1<<1);
LPC_TMR16B0->TCR &= ~(1<<1);By using above statements Timer Counter and the Prescale Counter are synchronously reset on the next positive edge of PCLK. The counters remain reset until TCR is returned to zero.

// Enable Timer-0 Interrupt
NVIC_EnableIRQ(TIMER_16_0_IRQn);The above statement enable the timer 16 interrupt, which will occur when TC values matches with the content of Match Register-0, Separate ISR handler is there for this interrupt which is named as TIMER16_0_IRQHandler(void), so ISR handler code will be written in this function.

// Start Timer
LPC_TMR16B0->TCR |= (1<<0);

The above statement will start the timer operation.

Green led is controlled using millis() function and Blue led is controlled using timer function, both are configured in such a way that led will toggle at the rate of 1 second.