Exception handling and PIC/EOI (x86)

文章来自：

http://compgroups.net/comp.lang.asm.x86/exception-handling-and-pic-eoi-x86/486611

"Bryan Bullard" <the_bullards@sbcglobal.net> wrote in message
news:xb28b.102$Vd1.33@newssvr24.news.prodigy.com...
> hello,
>
> this is probably a silly question.  however, i haven't found explicit
> information on the web and i need straight forward clarification.
>
> question 1:  obviously, if the PIC is initialized to require manual EOI,
the
> PIC must be acknowledged by sending EOI from the hardware interrupt
handler.
> however, i'm not sure if this is always required or only required if
higher
> priority hardware interrupts are to be serviced (nested). what is required
> for either condition?
(问题一：当PIC被初始化为手动EOI的时候，外部中断的例程通过发送EOI来通知PIC中断处理结束；可是我不确定是否总是要发送EOI，或者仅仅是高特权级别的外部中断运行的时候(需要发送)，以此来形成中断嵌套？)
Always required. The difference is when you send an EOI. When you want to
allow higher-priority interrupts to be serviced, you do it immediately so
your interrupt routine can be interrupted. You also need to set IF=1.
(答一：总是需要(发送EOI)。不同之处在于——什么时候发送EOI。当你希望搞特权级别的中断能够打断低特权级别中断的运行的时候，你应该在要被中断的中断例程开头发送EOI。同时，你需要设置 IF=1。)
> question 2:  do cpu exception handlers need to send and EOI to the PIC?  i
> would think not, and may cause problems i would think.  i'm wondering
> because i saw the unsubstantiated usage as such.
(问题二：CPU的异常处理例程需要发送EOI给PIC么？ !(- -))
No. Most exceptions generated by the CPU do not go through the PIC, so
sending EOI would confuse the PIC and may cause you to lose valid
interrupts. I believe one of the FPU exceptions (7??) used to require EOI
because it used to vector through the PIC, but I'm not sure how that's
changed with on-chip FP units. I *think* you still have to EOI for that. The
Intel Architecture manuals and/or APIC manual may have more information.
(答二：不需要。大多数的异常是由CPU产生，不经过PIC。)
> question 3:  the same question at question 2 only regarding software
> interrupts called by INT n.
>
> thanks,
> bryan

Never EOI on software interrupts. EOI is just a handshake to tell the PIC
that you got the interrupt and are processing it. If you're in a software
interrupt or exception (CPU-generated interrupt), the PIC is not a part of
the picture. The PIC only handles external interrupts.

-Matt

 

> > question 2:  do cpu exception handlers need to send and EOI to the PIC?
i
> > would think not, and may cause problems i would think.  i'm wondering
> > because i saw the unsubstantiated usage as such.
>
> No. Most exceptions generated by the CPU do not go through the PIC, so
> sending EOI would confuse the PIC and may cause you to lose valid
> interrupts. I believe one of the FPU exceptions (7??) used to require EOI
> because it used to vector through the PIC, but I'm not sure how that's
> changed with on-chip FP units. I *think* you still have to EOI for that.
The
> Intel Architecture manuals and/or APIC manual may have more information.

CPUs with on-chip FPU determine the way of raising the FP fault  by CR0.NE
(bit 5) value. When it's clear, ints are handled in MS-DOS style (that is,
via PIC). When set, they're handled in native (internal) way. See IA-32
maunal, Vol.3, Chap. 2.5 and Vol. 1, App. D for more info.

-Ivan