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RE: Interrupt vectors - idea of IRQ and interrupt name

> From: Nodir Qodirov
> I am trying to understand eCos interrupt mechanism (maybe interrupt
> mechanism itself in general). And now I have question may seem to be
> too simple, which every Embedded System developer should know. But I
> couldn't figure out:
> 1) Why do we have same values assigned to the eCos interrupts names
> and IRQs? Are they somehow mapped to each other through same value
> (32, 33, 34...).
> 2) Why value assigned starting from 32 (can't be it from "0")?
> I have found in packages\hal\i386\pcmb\current\include\pcmb_intr.h file:
> // Interrupt vectors.
> #define CYGNUM_HAL_INTERRUPT_IRQ0                32
> #define CYGNUM_HAL_INTERRUPT_IRQ1                33
> #define CYGNUM_HAL_INTERRUPT_IRQ2                34
>                    ...
> #define CYGNUM_HAL_INTERRUPT_IRQ15               47
> #define CYGNUM_HAL_INTERRUPT_TIMER                    32
> #define CYGNUM_HAL_INTERRUPT_KEYBOARD            33
> #define CYGNUM_HAL_INTERRUPT_SLAVE8259            34
>                   ...
> #define CYGNUM_HAL_INTERRUPT_HDD                       46
> Comment on file says "This file contains info about interrupts and
> peripherals that are common on all PCs; for example, the clock always
> activates irq 0 and would therefore be listed here." But I couldn't
> catch idea. Any resource to get more information to get better
> understanding of eCos interrupt mechanism?

Interrupt numbers are physical quantities tied to a particular architecture.
In the Intel architecture, there are 256 interrupts, and by convention the
external hardware ones start at 32 because lower-numbered ones are reserved
for CPU traps and such. If you look at a different architecture, such as
ARM, you'll see different assignments. All eCos does is provide a framework
in which interrupt sources can be identified by whatever numbers are
appropriate to the architecture.


Ciao,               Paul D. DeRocco

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