After some study, trial and error, I created a simple project for a NXP LPC1768, to test its timer interrupt. This project contains only startup_LPC17xx.s, system_LPC17xx.c, C-main.c, and timer.c.
C-main.c:
#include "lpc17xx.h" #include "timer.h" extern uint32_t SystemFrequency; int main(void) { SystemInit(); Timer_Init_n_Enable( LPC_TIM0, (SystemFrequency/8-1) ); NVIC_EnableIRQ(TIMER0_IRQn); /* LED Init */ LPC_GPIO2->FIODIR |= 0x000000FF; /* P2.0 to P2.7 LEDs defined as output */ while(1); }
timer.c:
#include "lpc17xx.h" #include "timer.h" void TIMER0_IRQHandler(void) { LPC_TIM0->IR = (1u<<0); // Reset the MR0 Interrupt; Writing a zero has no effect. LPC_GPIO2->FIOPIN ^= (1<<7); // Toggle LED. } void Timer_Init_n_Enable( LPC_TIM_TypeDef * TimerX, uint32_t TimerInterval ) { TimerX->MR0 = TimerInterval; TimerX->MCR |= (1u<<0) | (1u<<1); // Interrupt and Reset on MR0 TimerX->TCR |= (1u<<0); // Enable Timer Counter and Prescale Counter }
This project seemed to work.
But if I change the timer.c to:
void TIMER0_IRQHandler(void) { LPC_GPIO2->FIOPIN ^= (1<<7); // Toggle LED. LPC_TIM0->IR = (1u<<0); // Reset the MR0 Interrupt; Writing a zero has no effect. }
It doesn't work.
If I change the timer.c to:
void TIMER0_IRQHandler(void) { LPC_GPIO2->FIOPIN ^= (1<<7); // Toggle LED. LPC_TIM0->IR = (1u<<0); // Reset the MR0 Interrupt; Writing a zero has no effect. NVIC_ClearPendingIRQ(TIMER0_IRQn); }
It seemed to works.
I guess that, it doesn't work because I clear the LPC_TIM0->IR interrupt flag too late, so the NVIC generates a pending interrupt for LPC_TIM0->IR.
I don't have a LPC23xx now, so I can't verify my guess. I guess that, it will still work:
void Timer0Handler(void) __irq { FIO2PIN ^= (1<<7); // Toggle LED. T0IR = 1; /* Clear Interrupt Flag */ VICVectAddr = 0; /* Acknowledge Interrupt */ }
I think it is usual that, programmer needs to do something to identify which kind of interrupt was triggered, before clear the interrupt flag.
So, if my understanding is correct, how do I know that, I did NOT clear the interrupt flag too late within an ISR?
It is quite frustrated that, I can't even handle a simple timer interrupt properly. Maybe my understanding has never been correct.
void TIMER0_IRQHandler(void) { LPC_TIM0->IR = (1u<<0); LPC_GPIO2->FIOPIN ^= (1<<7); //=> LPC_TIM0->IR cleared already. } //===========================================> The ISR return.
void TIMER0_IRQHandler(void) { LPC_GPIO2->FIOPIN ^= (1<<7); //=> instruction port: done. LPC_TIM0->IR = (1u<<0); //=> instruction port: done; data port: not yet, LPC_TIM0->IR not cleared. } //===========================================> The ISR return. //===========================================> NVIC works on next Interrupt Handling. //===========================================> NVIC gets a LPC_TIM0->IR flag.
void TIMER0_IRQHandler(void) { LPC_GPIO2->FIOPIN ^= (1<<7); LPC_TIM0->IR = (1u<<0); NVIC_ClearPendingIRQ(TIMER0_IRQn);//=> LPC_TIM0->IR cleared already. } //===========================================> The ISR return.
Many thanks to Marcus.
I guess, If I am really trying to identify the interrupt source first, then clear the related interrupt flag right after, this symptom will not occur. Because before the ISR returns, all the interrupt flag updating has been done already.
I just joined the new company around two months. The trial period of new employee is generally three months. Somehow I can not get any available hardware for my development. (Just like in my ex-company.) So my supervisor let me use my private evaluation board, which I bought from eBay/ruten last year for personal study purpose. My supervisor asked me to do some basic practices like Key-Input and De-bounce, RTC based Date/Time Displaying. Actually most people here, don't know anything about ARM. I was told that, if I prefer ARM and I can handle ARM, I can use ARM for new projects; but it is quite doubtable. And in the Taiwanese culture, it is not wise to do something unusual, or ask for outside training of new technology, when you are the new guy.
RTC doesn't work, Strange Timer behavior, sounds like you are a quite lousy programmer.
MCU/Embedded System is very platform dependent; Yes, I know.
Good luck with the new job then.