David,
Thanks for you input, I managed to occasionaly get the count I required when performing the calculation in the second interrupt. As you suggested I got unstable results due to the count changing whilst doing the calculation. I want to use this to monitor frequency as part of a larger program, I therefore don't want to spend lots of time doing this calculation.
I understand what you mentioned about interrupt priority so have attempted to produce code to compensate. I am using codwarrier so have no problems with the maths library. The code is below if you could give me any hints I have not yet tested this version so don't know if it works. This is my first microcontroller project and I am learning 'C' as I go so I appologise for my, probably, not very efficient code.
Confused and Fustrated
Martin
#define TRUE 1
#define FALSE 0
volatile unsigned int first, second, count, count1, count2, a, b;
volatile float time;
void main()
{
volatile unsigned int countstart, countend;
for(;
{
if(b == TRUE){
asm SEI /* Disable interrupt */
countend = count2; /* Save globals as locals */
countstart = count1; /* Save globals as locals */
time = ((65536*(countend-countstart))+second) - first; /* Calculate total count */
}
/* Turn on timer subsystem */
TSCR1 = 0x80; /* Enable */
TFLG2 = 0x80; /* Enable timer overflow interrupt */
/* Setup for IC5 */
TIOS = TIOS & ~0x20; /* Configure PT5 as IC */
TCTL3 = 0x04; /* Capture Rising Edge */
TFLG1 = 0x20; /* Clear IC5 Flag */
TIE = 0x20; /* Enable IC5 Interrupt */
/* Setup for IC6 */
TIOS = TIOS & ~0x40; /* Configure PT6 as IC */
TCTL3 = 0x20; /* Capture falling Edge */
TFLG1 = 0x40; /* Clear IC6 Flag */
TIE = 0x40; /* Enable IC6 Interrupt */
asm CLI
}
}
interrupt void tim0_ch5_isr(void)
{
first = 0;
second = 0;
count = 0;
first = TC5;
TSCR2 = 0x80; /* Enable counter */
TFLG1 = 0x20;
a = TRUE; /* bit set to ensure overflow and ch6 interrupt occur after ch5 interrupt */
}
interrupt void tim0_overflow_isr(void)
{
if(a == TRUE){
TFLG2 = 0x80; /* Clear overflow flag ch5 */
if(first == 0){ /* code to conteract interrupt priority */
count1 = count - 1;
count1++;
}else{
count1 = count;
count1++;
}
}
}
interrupt void tim0_ch6_isr(void)
{
if(a == TRUE){ /* Operate only after ch5 interrupt has occurred */
TFLG1 = 0x40; /* Clear overflow flag ch6 */
second = TC6;
count2 = count; /* Store final count */
b == TRUE; /* bit set when both ch interrupts have occured */
}
}
David,
Thanks for the advice, I seem to be getting closer to solving the problem. I hopefuly want to use the timer to both monitor frequency and to measure the phase angle between a voltage and current signal, from the output of a small generator. This is why I have been using the two interrupts, I thought if I could, figure this out I could easily implement frquency measurement using one interrupt. I realise I am measuring duty cycle but until I connect to the test generator I do not have a method of generating a two synchronised but out of phase signals.
I feel the problem I having is counting the timer overflow interrupts, I thought I would be able to enable the overflow interrupt during the interrupt for the first edge. and set the counter to zero and then count until the second edge occurs.
interrupt void tim0_ch5_isr(void)
{
TFLG1 = 0x20;
first = TC5;
count = 0;
TSCR2 = 0x80
a = TRUE;
}
interrupt void tim0_overflow_isr(void)
{
TFLG2 = 0x80;
count++;
}
interrupt void tim0_ch6_isr(void)
{
TFLG1 = 0x40;
if(a == TRUE){
first1 = first;
second = TC6;
count1 = count;
b = TRUE;
}
}
It does catch the correct value occasionally but often over and under counts. I have used the a and b variables so that the second time isn't taken until the first has occured and the time isn't calculated until both have occured. I haven't been able to establish any priority problems, could be due to lack of debugging knowledge, but the documentation states that the input capture events have priority over the overflow, i.e. ch5, ch6 then overflow.
I have removed the timer setup instrunctions into a seperate function called from outside the main loop and put the time calculation into a IF statement, which should only operate if both interrupts have occured. I am using the asm SEI statement to disable interrupts while save the variables, is this correct? I then enable interrupts do the calculation and clear a and b variables.
void main()
{
unsigned int start, end, Tcount, time;
for(;{
timerset();
if((a == TRUE) && (b == TRUE)){
asm SEI
start = first1;
end = second;
asm CLI
time = ((65536*Tcount)+end) - start; /* Calculate total time */
a = FALSE;
b = FALSE;
}
}
}
For a 50Hz signal with the controller running in boot mode 24MHz, I calculated the timer overflow should occur 3 times (possibly 4 depending on timing of capture) . With the the interrupt timing problems you mentioned the overflow count should be no more than one count out from this value. I, however, am getting counts ranging from 0 to 12. Any ideas?
Thanks
Marti
