Re: [avr-gcc-list] interrupts and signals (again)

[David Kelly]

On Mar 26, 2005, at 8:41 AM, Parthasaradhi Nayani wrote:

> Firstly you need to get clarity on how interrupts are
> handled by processors.
> 1. Priority of interrupts will come into picture only
> when two or more interrupts occur at the same time.

On more advanced CPU's interrupts behave as Jamie was asking. That only 
a higher priority interrupt can suspend a lower priority handler in 
execution.

On microcontrollers where low cost and high volume is the name of the 
game it was once common to have only one interrupt vector, or none. Off 
the top of my head a Microchip 16C55x has one IRQ which shares the same 
vector as power up. One has to determine which event happened in 
software.

AVRs are pretty advanced with lots of IRQ vectors, most are self 
clearing.

IMHO if you are worrying about the amount of time your service routine 
requires to execute then its written wrong. The routine should be 
prepared that when its called it can do its thing quickly and jump back 
out. UART code should do nothing more than buffer data. Decode serial 
data outside of interrupt time.

I use SIGNAL() because my service routines execute quickly and I don't 
want an  indeterminate state caused by stacking one IRQ on top of 
another.

--
David Kelly N4HHE, address@hidden
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Whom computers would destroy, they must first drive mad.