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TM4C129 - incorrect period

Daniel daniel
Intellectual 330 points

Hello Guys,

I am using the TM4C1294NCPDT part of the launchpad (EK-TM4C1294XL).

I am trying to run a timer at 1 microsecond interrupts. I am getting 0.55usec however. I am not sure what is wrong with my calculations. I toggle a GPIO pin, in the interrupt. I have used the timer interrupt code in the  workbook (page 118)  provided by T1 called: Creating IoT Solutions with the Tiva® C Series Connected LaunchPad Workshop.

I am using the following period calculations.

if we relate the clock rate by the time: 120,000,000 cycles/sec= 1 second

and 1 second = 1usec*1,000,000

then 120,000,000=1*1,000,000

or 1usec=120,000,000/1,000,000 = ui32SysClkFreq/1,000,000.

the output can be viewed here, or http://imgur.com/ULJiZOb :

The code: http://pastebin.com/AWWzn77W



The project file:proj.zip




Thanks Guys



								


				
				

				
			

		

			
						
									
                			    			            
						
						
			
			
			
			                        
			

				

			


			

		


				    			

						

















	

	

					
    
	
    





		
	
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                          TI__Guru
                        59540 points
                      
    
                          
                   		
		
    
					
    Hello Daniel,
    

    
If you review the example, you can note that the clock is acutally divided by 2 to generate an interrupt on both the low to high transition and the high to low transitions to get to the desired period for the generated output with 50% duty cycle. Given this information, the period should actually be 2usec not 1 as you have coded. So, I believe you would need a period = (SysClk/1000000)/2 to achieve the 1usec pulse width on the output which would equate to a 1us timer interrupt.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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						in reply to Chuck Davenport
					
									
    
	
    
	                                    
                      
    
                        
                          Intellectual
                        330 points
                      
    
                          
                   		
		
    
					
    thanks chuck, however the problem was with my code, I forgot to clear the timer register in the interrupt. the working code.
    

    #include <stdint.h>
#include <stdbool.h>
#include "inc/tm4c1294ncpdt.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/sysctl.h"
#include "driverlib/interrupt.h"
#include "driverlib/gpio.h"
#include "driverlib/timer.h"


int main(void)
{
	uint32_t ui32Period;
	uint32_t ui32SysClkFreq;

	ui32SysClkFreq = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ | SYSCTL_OSC_MAIN |
	SYSCTL_USE_PLL | SYSCTL_CFG_VCO_480), 120000000);
	//clock init
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);

	//GPIO init
	GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1);
	//timer init
	TimerConfigure(TIMER0_BASE, TIMER_CFG_PERIODIC);

	ui32Period = ui32SysClkFreq/1000000;

	TimerLoadSet(TIMER0_BASE, TIMER_A, ui32Period -1);

	IntEnable(INT_TIMER0A);
	TimerIntEnable(TIMER0_BASE, TIMER_TIMA_TIMEOUT);
	IntMasterEnable();

	TimerEnable(TIMER0_BASE, TIMER_A);





while(1)
	{
	}
}

volatile int x = 2;
void Timer0IntHandler(void)
{
	 TimerIntClear(TIMER0_BASE, TIMER_TIMA_TIMEOUT);

	x^=0xF;
	GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1, x);


}
    

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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