Interrupt question

[ultiblade]

Hi !

I have a small question. If i use the following code:

;==== Dec's for OSC 
DEFINE OSC 8                                            'Int OSC @ 8 MHz, for PBP
OSCCON      = %01110001                                 'Int OSC @ 8 MHz

'==== Interrupt handler 
on interrupt goto intHANDLER

'==== Set defines 
OPTION_REG  = %10000000                                 'Set Weak pull-ups
WPU         = %00000000                                 'Weak pull-ups disabled
INTCON      = %11000000                                 'Enable unmasked perhipal interrupts
PIE1        = %00000001                                 'Set TMR1 overflow interrupt
PIR1        = %00000000                                 '
PCON        = %00000000
IOC         = %00000000                                 'Interrupt On Change disabled
PCON        = %00000000                                 'Ultra lowpower + BOR disabled
ANSEL       = %00000000                                 'GPIO 0 Analog
TRISIO      = %00101000                                 'GPIO 0,3 inputs
GPIO        = %00000001                                 'All I/O low
CMCON0      = %00000111                                 'Comparator off
CMCON1      = %00000000                                 'Output is synced with TMR1
VRCON       = %00000000                                 'Voltage ref. disabled
ADCON0      = %00000000                                 'ADC off
T2CON       = %00000100                                 'TMR2 = ON, prescaler = 1:1                                  
T1CON       = %10000111                                 'Timer1 counts 100Hz
CCP1CON     = %00000000                                 'CCP engine is off


'==== Dec's for variables
countLOOP   var word
synclong		var word

'==== Initialise variables
countLOOP   = 0
     
'==== Set timer1 3000 from overflow
synclong = 65535-3000
TMR1H = synclong.highbyte
TMR1L = synclong.lowbyte

'==== Main program
start:	
GPIO.0  =1															'pulse 1 on
pauseus 800																									'Pause 800 us
GPIO.0 = 0																									'pulse 1 off
pauseus 800																									'pause 800 us
goto start

'==== The End =======================================================================
theend:                                                			'Endless loop
goto theend

'==== Interrupt handler 
DISABLE
intHANDLER:                                                 'Disable interrupts
    intdelay = 1                                       		  'Set interrupt has occured bit
    PIR1.0 = 0																							'Clear interrupt
    TMR1H = synclong.highbyte																'Set Tmr1 3000 from overflow again
    TMR1L = synclong.lowbyte
    resume
enable

Tmr1 is setup as a counter. If it overflows within one of the the 800us delays, will the interrupt be fired directly, or will it first finish the 800us and then fire ?

Should i be using the DT instant interrupts ? I've noticed that the DT interrupts can't resume to a specific label, am i right ?

Thanks
UB

[HenrikOlsson]

Hi,
The interrupt flag will be set as soon as TMR1 overflows but PBP won't "see" it until the PauseUs statement is completed. Hence, the ISR won't be executed until after the pause.

Using DTInts won't give you that problem.

[ultiblade]

OK ! I will give the Dtint a try ...

Thanks for the fast reply !

Best regards,
UB

[ultiblade]

Just wondering. With the pbp ON INTERRUPT STATEMENT i could do a RESUME to a specific label.

This is not possible with the DT int, right ?

[Charles Linquis]

DT interrupts can't return to a specific label - but you can set a flag inside the ISR and test for that in your main program loop. If set, you can jump to wherever you want.

Although it isn't quite "instant", that method can usually accomplish what you need.