sos.c

/**
 * SOS.c by Iliyan Stankov
 * Runs on TM4C123 LaunchPad
 * Input from PF4(SW1),PF0(SW2), output to PF3 (Green LED)
 * Pressing SW1 starts SOS (Green LED flashes SOS).
 * Pressing SW2 stops SOS
 */

// Constant declarations to access port registers using 
// symbolic names instead of addresses
// ##########################################################################
// # Variable to hold register addresses
// # These registers control how the peripherals on the chip are set up
// # These include I/O ports, timers etc.
// # (registers, their use and memory locations are listed in data sheet)
// ##########################################################################
#define GPIO_PORTF_DATA_R    (*((volatile unsigned long *)0x400253FC))
#define GPIO_PORTF_DIR_R     (*((volatile unsigned long *)0x40025400))
#define GPIO_PORTF_AFSEL_R   (*((volatile unsigned long *)0x40025420))
#define GPIO_PORTF_PUR_R     (*((volatile unsigned long *)0x40025510))
#define GPIO_PORTF_DEN_R     (*((volatile unsigned long *)0x4002551C))
#define GPIO_PORTF_LOCK_R    (*((volatile unsigned long *)0x40025520))
#define GPIO_PORTF_CR_R      (*((volatile unsigned long *)0x40025524))
#define GPIO_PORTF_AMSEL_R   (*((volatile unsigned long *)0x40025528))
#define GPIO_PORTF_PCTL_R    (*((volatile unsigned long *)0x4002552C))
#define SYSCTL_RCGC2_R       (*((volatile unsigned long *)0x400FE108))

// Global Variables
unsigned long SW1; // input from PF4
unsigned long SW2; // input from PF0

// Function Prototypes
void PortF_Init(void);
void Flash_SOS(void);
void delay(unsigned int halfsecs);
 

/** 
 * MAIN: Controls the order of operations
 */
int main(void)
{
	PortF_Init(); // Init port PF4 PF2 PF0    
	while(1)
	{
		do
		{
			SW1 = GPIO_PORTF_DATA_R&0x10; // PF4 into SW1
		}
		while (SW1 == 0x10);

		do
	    	{
			FlashSOS();
			SW2 = GPIO_PORTF_DATA_R&0x01; // PF0 into SW2
	    	}
	    	while(SW2 == 0x01);
	}
}


/**
 * Subroutine to initialize port F pins for input and output
 * PF4 is input SW1 and PF2 is output Blue LED
 */
void PortF_Init(void)
{
	volatile unsigned long delay;
	// ###########################################
	// # Here we set up the peripherals on the chip.
	// #
	// # First we set the clock speed.
	// # Here we do “current register value” = “current register value” OR hexadecimal 20
	// # This sets a bit in the RCGC settings in the  “Run-Mode Clock 
	// # Configuration (RCC)” register which chooses the
	// # “Precision internal oscillator / 4” as the clock signal for the chip
	// ###########################################
	SYSCTL_RCGC2_R |= 0x00000020;    // 1) F clock
	
	// # Not sure what this variable is for.....
	// # The variable is being set to a register address
	delay = SYSCTL_RCGC2_R;          // delay   
	
	GPIO_PORTF_LOCK_R = 0x4C4F434B;  // 2) unlock PortF PF0  
	GPIO_PORTF_CR_R |= 0x1F;         // allow changes to PF4-0       
	GPIO_PORTF_AMSEL_R &= 0x00;      // 3) disable analog function
	GPIO_PORTF_PCTL_R &= 0x00000000; // 4) GPIO clear bit PCTL  
	GPIO_PORTF_DIR_R &= ~0x11;       // 5.1) PF4,PF0 input, 
	GPIO_PORTF_DIR_R |= 0x08;        // 5.2) PF3 output 
	GPIO_PORTF_AFSEL_R &= ~0x1F;     // 6) no alternate functions
	GPIO_PORTF_PUR_R |= 0x11;        // enable pullup resistors on PF4,PF0       
	GPIO_PORTF_DEN_R |= 0x1F;        // 7) enable digital pins PF4-PF0        
}

/**
 * Subroutine to Flash a green LED SOS once
*/
void Flash_SOS(void)
{
	// S
	// # Turn bit on, delay.....
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	// # Turn bit off, delay....
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	
	// O
	GPIO_PORTF_DATA_R |= 0x08;  delay(4);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(4);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(4);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	
	// S
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	GPIO_PORTF_DATA_R |= 0x08;  delay(1);
	GPIO_PORTF_DATA_R &= ~0x08; delay(1);
	
	delay(10); // Delay for 5 secs in between flashes 
}
 
/**
 * Subroutine to delay in units of half seconds
 * Inputs: Number of half seconds to delay
 */
void delay(unsigned int halfsecs)
{
	unsigned long count;
	while (halfsecs > 0 ) // repeat while still halfsecs to delay
	{
		count = 4000000;

		while (count > 0) // Takes approximately 0.5 secs
		{ 
			count--;
		}
		halfsecs--;
	}
}