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

[David Kelly]

On Mar 26, 2005, at 12:25 PM, Larry Barello wrote:

> The intel x86 interrupt controller family comes to mind.  This is 
> ancient
> history, but the i8259 comes to mind.  I think all that stuff is 
> embedded in
> the CPU chips now days.

Yes, the i8259 commonly used on x86's, believe it was the MC68910 on 
68k's, and most all high end 16 and 32 bit microcontrollers such as 
Coldfire, embedded x86's, etc. Some of the Freescale MCU's have 
databooks of hundreds of pages dedicated to just one module, such as an 
IRQ controller.

> If you think of interrupts as the hardware equivalent to tasks in an 
> OS,
> then priority and pre-emption makes sense.  The AVR has priority (the 
> order
> of the vector table) but not priority based pre-emption.

Yup. And what really gets hairy is if you re-enable the I bit in a 
handler and then *its* hardware trips and re-enters before the first 
instance is complete. Then again that is quite handy for creating a 
multitasker.

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