int main (void) 
{
        SystemInit();                             /* initialize clocks             */

        /* Setup GPIO for LEDs                                                     */
        RCC->APB2ENR |=  1 <<  6;                 /* Enable GPIOE clock            */
        GPIOE->CRH    = 0x33333333;               /* Configure the GPIO for LEDs   */

        GLCD_Init();                              /* Initialize the GLCD           */
        GLCD_Clear(White);                        /* Clear the GLCD                */
	
	//Enable Port B clock and configure USART1 (with remapping of USART1 to Port B from Port A)
	RCC->APB2ENR |= 1 << 3;
	RCC->CFGR  |= 4 << 10;
	RCC->APB2ENR |= 1 << 0;
	AFIO->MAPR |= 1 << 2;
	
	//Enable GPIOB7 as rx, GPIOB6 as tx (Pin7: 0100, Pin6: 1011)
        GPIOB->CRL &= 0x00FFFFFF;
        GPIOB->CRL |= 0x4B000000;	
	
	//Enable USART in RCC_APB2ENR
	RCC->APB2ENR |= 1 << 14;
	
	/*
	Set baud rate (USART_BRR): BaudRate =   fck / ( 16 * USARTDIV )
	    For example:
	        fck = 72 MHz
		    required Baud Rate = 9600
		 
		    USARTDIV = fck/(16 * BaudRate ) = 72000000/(16 * 9600) = 468.75
		 
		    Mantissa = 438 - as hex: 0x1D4
		    Fraction = 16*0.75 = 12 - as hex: 0xC
			
		    See Reference Manual for further details
	*/ 
	USART1->BRR = 0x01d4c;
	
	//USART enable
	USART1->CR1 |= 1 << 13;
	
	//USART Tx enable
	USART1->CR1 |= 1 << 3;
	
	//USART Rx enable
	USART1->CR1 |= 1 << 2;
	
	//USART Rx Interrupt enable
	USART1->CR1 |= 1 << 5;
	
	//Send initialisation messages to the GPS, 1: Baud rate, 2: Reset GPS to output default NMEA messages
	putstr("$PMTK251,9600*17\r\n");
	putstr("$PMTK314,-1*04\r\n");
	
	NVIC_EnableIRQ(USART1_IRQn);

        os_sys_init (init);        /* Initialize RTX and start init */
}

void usart1_tx(char character) 
{
	while ((USART1->SR & ( 1 << 6)) == 0) {}; // Wait HSERDY = 1
	USART1->DR = (uint16_t) character;
}

void putstr(char *string) 
{
	int i;
	for ( i=0; string[i] != 0; i++ )
        {
		usart1_tx(string[i]);
	}
}

//USART1 Interrupt Handler

void USART1_IRQHandler(void) __irq
{
	NVIC_DisableIRQ(USART1_IRQn);
	
	//Send event flag to t_gps task
	isr_evt_set(0x1111, t_gps);	
	
	//Reset USART status register to allow the next value from the serial link to be set
	USART1->SR &= ~(1 << 5);
	
	NVIC_EnableIRQ(USART1_IRQn);
}

// Global array received[] used to allow output to be seen in debugger.
// Use of the global array would also be relevant to allow data to be passed between tasks.
// This approach would require use of mutexes when writing to and reading from the array, to ensure that only complete messages are saved 
// This is a very minimal implementation to allow viewing of received messages in the debugger.
// More work is required to make a robust character buffer...

__task void gps(void)
{
	int i = 0;
        for(;;)
	{
	     os_evt_wait_and(0x1111, 0xffff);
	     received[i] = USART1->DR;
		
             // Check for standard NMEA message ending (CR/LF)             
             if(received[i]==0x0A  && received[i-1]==0x0D)
	     {
                i=0;
	     }
	     else
	     {
	         i++;
	         i=i%MAX_MESSAGE_SIZE;
	     }
	}
}

OS_TID t_phaseA;                        /* assigned task id of task: phase_a */
OS_TID t_phaseB;                        /* assigned task id of task: phase_b */
OS_TID t_phaseC;                        /* assigned task id of task: phase_c */
OS_TID t_phaseD;                        /* assigned task id of task: phase_d */
OS_TID t_clock;                         /* assigned task id of task: clock   */
OS_TID t_lcd;                           /* assigned task id of task: lcd     */
OS_TID t_gps;			        /* assigned task id of task: gps     */

OS_MUT mut_GLCD;                        /* Mutex to control GLCD access     */

#define LED_A   0
#define LED_B   1
#define LED_C   2
#define LED_D   3
#define LED_CLK 7

#define LED_NUM     8                   /* Number of user LEDs                */

#define MAX_MESSAGE_SIZE 100
const long led_mask[] = { 1<<15, 1<<14, 1<<13, 1<<12, 1<<11, 1<<10, 1<<9, 1<<8 };
unsigned char received[MAX_MESSAGE_SIZE];