Content originally posted in LPCWare by gillys on Fri May 11 19:23:41 MST 2012 Hello,
I am confused about the code I attached below. For small values of PWM_VALUE the code works fine (LED is nearly off). For increasing values of PWM_VALUE the LED gets brighter. But for values near the value from LPC_TIM0->MR0 (e.g. 995) the LED is nearly off, however it should be almost the maximum brightness. What is wrong about my code?
#ifdef __USE_CMSIS
#include "LPC17xx.h"
#endif
#include <cr_section_macros.h>
#include <NXP/crp.h>
__CRP const unsigned int CRP_WORD = CRP_NO_CRP ;
enum {
PCTIM0 = 1, MR0 = 0, MR1 = 3
};
int main(void) {
LPC_SC->PCONP |= (1 << PCTIM0); // turn power for TIMER0 on
LPC_TIM0->MR0 = 1000; // match register 0
LPC_TIM0->MCR |= (0x3<< MR0); // Interrupt + reset
LPC_TIM0->MR1 = PWM_VALUE; // match register 1
LPC_TIM0->MCR |= (0x1<< MR1); // interrupt if MR1 = TC
LPC_TIM0->TCR = 1; // enable Timer0
NVIC_EnableIRQ(TIMER0_IRQn);
LPC_GPIO0->FIODIR |= (1 << 22); // LED pin
while(1) asm volatile("nop");
return 0 ;
}
void TIMER0_IRQHandler(void)
{
if (LPC_TIM0->IR & (0x1 << 0)) //Interrupt flag for match channel 0.
{
LPC_TIM0->IR = (0x1 << 0); //kill flag
LPC_GPIO0->FIOSET |= (1 << 22);
}
if (LPC_TIM0->IR & (0x1 << 1)) //Interrupt flag for match channel 1.
{
LPC_TIM0->IR = (0x1 << 1); //kill flag
LPC_GPIO0->FIOCLR |= (1 << 22);
}
}
Content originally posted in LPCWare by gillys on Sat May 12 10:41:54 MST 2012 Quote: Zero I'm also confused about your code. And your LPC1769 is confused, too. What are you trying to do? :) Thank you very much! You helped me a lot!
Content originally posted in LPCWare by Ex-Zero on Sat May 12 04:25:25 MST 2012 Quote:
I am confused about the code I attached below. I'm also confused about your code. And your LPC1769 is confused, too. What are you trying to do?
You are running a 25MHz timer to switch a LED with 25kHz.With (1000-995)* 1/25MHz there are 200ns left for you interrupt :eek:
Believe it or not, interrupts need time :mad:
So what's happening here is easy to explain:
Your interrupt handler is getting both interrupts. Instead of setting or resetting your LED, it's doing both. And exactly in that order you've programmed :rolleyes: As result you are generating a little pulse in your interrupt handler.
Possible solutions
#1 Give your hard working interrupt handler a little bit more time.[INDENT] Use a prescaler if it's possible for your LED to run with 2.5kHz instead of 25kHz.
LPC_TIM0->PR = 9; //prescaler 10
[/INDENT]#2 Don't use interrupts. This chips can generate PWM without interrupts.[INDENT] This sample is generating a real PWM at PWM1.1 (P2.0) without interrupts:
