Global Interrupt

[christian.koji]

Hey Guys,

i'm with a doubt. I'm not sure when i should use global interrupt and when i shouldn't.

[Ttelmah]

If you are using any interrupt, and want a handler to be called, you also need to enable the global interrupt.

Interrupts are a 'layered' structure. You have the hardware event, which triggers the interrupt. Then, If the specific interrupt enable flag for that interrupt _and_ the global interrupt enable flag are both set, the interrupt handler will be called.
If you have an interrupt enabled, and the global flag disabled, then no handler will be called, _but_ if you are using 'sleep', the processor will wake up.
Think of it like a lighting system. The global interrupt flag, is the 'master switch' in the fuse box. If this is off, the lights won't work. If this is on, nothing will happen, unless the specific light switch is on (the interrupt enable flag for the particlar interrupt), and there is a bulb in the light (the actual interrupt flag).

Best Wishes

[christian.koji]

LOL good analogy =P

Guess i undertand now..
in the datasheet is saying that:
GIE=1 Enables all unmasked interrupts
GIE=0 Disables all interrupts

what is a masked interrupt?

for example on my code i have three interrupt
enable_interrupts(INT_SSP); //enable I2C interrupts
enable_interrupts(INT_EXT);
enable_interrupts(GLOBAL);

if i disable global interrupt the MSSP and the portB0 wont generate an interrupt?

if i have only the global interrupt enabled, then i have to test the bits all by myself... right?
i mean i have to do, if(tmr0if){ ... }else if(int0if){ .. }

[Ttelmah]

The operation 'enable_interrupts(INT_SSP)' 'unmasks' this interrupt.
All interrupts default to being 'masked off'.
You need to separate the idea of the global interrupt _handler_ from the global interrupt 'mask'.
The enable_interrupt instruction, affects the mask.
The enables/disables, all affect 'mask bits' that control what happens (the switches in the analogy).
If you only have one interrupt handler, and this is defined at #int_global, then this handler is called for all interrupts. In this, you need to do the following:
1) Save all registers that are changed in your handler code.
2) Test for an interrupt being enabled, _and_ it's flag set. If both are true, call it's handler.
3) Clear the interrupt.
4) Restore the registers

Best Wishes