Yes I realized that if I read the PWM0CR0 register multiple times in the
same interrupt it has different values and in the end it is confused me. I
was able to solve the problem and now I read the values correctly.
I read the register once per interrupt and store it in a variable and do
operations on the value in the variable rather than the PWM0CR0 register
itself.
Finally I can move on with my life :)
Regards
Sneha
Reply by zdra...@yahoo.com●February 10, 20142014-02-10
Hello,
First let me clarify that the code snippet which I posted is just an
example.
Since PWM0CR0 is declared as volatile, the compiler issues a read operation
every time you use it in a read context.
Of course you need to read PWM0CR0 for both falling and rising edge. But my
remark was to read it once per IRQ.
In your code:
void Capture0IntrHandler(void)
{
if ((PWM0IR == 0x10)){
if((PWM0CCR_bit.CAP0RE == 1)){ //low to high transition rising edge
period = PWM0CR0 - rising_edg;
rising_edg = PWM0CR0;
PWM0CCR = 0x6;
}else{
duty = PWM0CR0 - rising_edg;
PWM0CCR = 0x5;
PWM0_Done =1;
}
}
PWM0IR=0xFF; //Reset the interrupt*/
VICADDRESS = 0;
}
In this code you have read of PWM0CR0 twice per IRQ. Twice per rising edge and
twice per falling edge.
In some situations this may be unsafe if a capture event occurs between the two
readings. Of course I can not bet that this is your case. But it will be good if
you correct your code.
You are rigth if the PWM is used as a counter you can not use the capture
feature. This I know from experience and it is not mentioned in the
documentation.
Regards
Zdravko Dimitrov
Reply by Sneha Nidhi●February 10, 20142014-02-10
Hello.
Thanks for your reply.
But I still have some questions. I wanted to read both high and low times
hence I was reading the PWM0CR0 register twice at rising and falling edge.
If I read it only once in the rising edge how do I get my falling edge? I
think I have a problem in counting the falling edge of the register.
Apart from that I also have some other doubts about the registers:
PCLKSEL0_bit.PCLK_PWM0 = 1; Can this be also used to set the pclk divisor
for the capture input or is it only for PWM funactionality.
I want to use this PCAP0.0 pin as a counter. In the datasheet we have to
set the
PWM0CTCR_bit.CM = 0;
PWM0CTCR_bit.CIS = 1; to enable the rising edge counter mode one needs to
set this pin.
And if the counter mode is enabled the pins @CCR as must be 000 as set. ref
UM10237 datasheet pg 643
But when I do this setting i am not receiving an interrupt from the sensor.
But if I set the PCAP0.0 pin as a timer
PWM0CTCR_bit.CM = 0;
PWM0CTCR_bit.CIS = 0; and CCR for rising edge 0x5 and falling edge 0x6
PWM0CCR_bit.CAP0RE = 1; //capture of rising edge
PWM0CCR_bit.CAP0FE = 0; //disable falling edge capture
PWM0CCR_bit.CAP0INT = 1; //enable interrupt rising edge 0x5
later I change in the interrupt to 0x6 for falling edge I am able to detect
the interrupt but the counter doesnt have the correct values.
Is there something wrong in my understanding of the code?
Thanks and Regards
Sneha
Reply by zdra...@yahoo.com●February 8, 20142014-02-08
Hello Sneha,
I have some points to mention:
1. You are using PWM as a freeruntimer. If you have a situation when PWM0CR0 <
rising_edg
period = PWM0CR0 - rising_edg;
will give you erroneus result.
2. You are reading PWM0CR0 twice in the PWM ISR. It is good practice to use:
Keep in mind that reading a register of the PWM address space is a read of an
APB address space register. Which, as I remmember, takes about 13 cloks to
complete for the leading read operation. So for consistency it is better to read
PWM0CR0 just once in the ISR.
3. In the main() you have:
t1 = duty;
t2 = rising_edg;
k = (double)t1/t2;
I think it should be:
t1 = duty;
t2 = period;
k = (double)t1/t2;
Regards
Zdravko
Reply by sneh...@gmail.com●February 7, 20142014-02-07
Hello everyone.
I am a newbie in lpc devices. I have been trying to interface the PWM based
max6672 sensor with the PWM capture pin. I want to read the both the low time
and high time of the PWM pulse. I am recieving an interrupt when the PWm input
is received. But some how I am not able to calculate the rise and fall time
correctly. I need this info to calculate the temperature of the sensor.
Steps in my code:
1. set up the PWM capture pin.
2. set the PWM capture registers.
3. Wait for interrupt on rise time. save the PWM0CR0 rise time value
4. set the register to low time interrupt.
5. wait for interrupt on low time. save the PWM0CR0 low time value = PWM0CR0 -
high time.
6. calculate the temp using the high and low time of the pulse.
I am putting up my code here.
void Capture0IntrHandler(void)
{
if ((PWM0IR == 0x10)){
if((PWM0CCR_bit.CAP0RE == 1)){ //low to high transition rising edge
period = PWM0CR0 - rising_edg;
rising_edg = PWM0CR0;
PWM0CCR = 0x6;
}else{
duty = PWM0CR0 - rising_edg;
PWM0CCR = 0x5;
PWM0_Done =1;
}
}
PWM0IR=0xFF; //Reset the interrupt*/
VICADDRESS = 0;
}
void init_timer(void) // Timer 0 used as a counter
{
// PWM PCAP0.0 Pin: P1.12
// pclk = cclk/2 = 30MHz (cclk=ARM7 core clock)
