IRQs in Pmode

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BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER 13 Jun 2011, 11:26

Hi everyone!
I've made interrupts and they do work, now I need to know how to handle IRQs in protected mode. I read on bonafide that I will have to map them somehow, how???

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NSOS

13 Jun 2011, 11:26

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20761
Location: In your JS exploiting you and your system

revolution 13 Jun 2011, 11:37

BOTOKILLER wrote:

... I will have to map them somehow, how???

Use the IDTR luke.

Intel Manual 3A, Chapter 6, Section 10 "INTERRUPT DESCRIPTOR TABLE (IDT)"

13 Jun 2011, 11:37

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER 13 Jun 2011, 14:55

I know that I have to use IDT, but what interrupt numbers IRQs occupy???

13 Jun 2011, 14:55

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20761
Location: In your JS exploiting you and your system

revolution 13 Jun 2011, 15:11

I assume then that you are asking about the hardware interrupt numbers? If so then you need to program the PIC chips to set the base value.

13 Jun 2011, 15:11

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 13 Jun 2011, 15:17

Yes you need to remap them, something like this:

Code:

remap_pic:
       cli
 mov  al,0x11                                      ; put both 8259s in init mode
     out  0x20,al
        out  0xA0,al
        mov  al,0x20                                      ; remap pic irq0-irq7 -> int 0x20-27
   out  0x21,al
        mov  al,0x28
        out  0xA1,al                                      ; remap pic irq8-irq15 -> int 0x28-30
  mov  al,4                                         ; icw3 pic1(master)
       out  0x21,al                                      ; bit 2=1: irq2 is the slave
  mov  al,2                                         ; icw3 pic2
       out  0xA1,al                                      ; bit 1=1: slave id is 2
      mov  al,1                                         ; icw4 to both controllers
        out  0x21,al                                      ; bit 0=1: 8086 mode
  out  0xA1,al
mask_irqs:    
  cli
 mov  al,255                                       ; mask all irqs
   out  0xa1,al
        out  0x21,al
        ret

13 Jun 2011, 15:17

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER 15 Jun 2011, 12:08

Dex4u wrote:

Yes you need to remap them, something like this:

Code:

remap_pic:
     cli
 mov  al,0x11                                      ; put both 8259s in init mode
     out  0x20,al
        out  0xA0,al
        mov  al,0x20                                      ; remap pic irq0-irq7 -> int 0x20-27
   out  0x21,al
        mov  al,0x28
        out  0xA1,al                                      ; remap pic irq8-irq15 -> int 0x28-30
  mov  al,4                                         ; icw3 pic1(master)
       out  0x21,al                                      ; bit 2=1: irq2 is the slave
  mov  al,2                                         ; icw3 pic2
       out  0xA1,al                                      ; bit 1=1: slave id is 2
      mov  al,1                                         ; icw4 to both controllers
        out  0x21,al                                      ; bit 0=1: 8086 mode
  out  0xA1,al
mask_irqs:    
  cli
 mov  al,255                                       ; mask all irqs
   out  0xa1,al
        out  0x21,al
        ret

thanks works fine, but mask must be 0, so that interrupts work

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NSOS

15 Jun 2011, 12:08

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 15 Jun 2011, 15:40

BOTOKILLER wrote:

thanks works fine, but mask must be 0, so that interrupts work

Yes, but first you should mask all interrupts first, than un-mask the ones you have implemented.
Which in most cases it all of them.

Code:

unmask_irqs:
  mov  al,0                                         ; unmask irq's 
  out  0xA1,al
        out  0x21,al
        sti
 ret

But not always Wink

15 Jun 2011, 15:40

christiandy

Joined: 03 Mar 2011
Posts: 25
Location: 101

christiandy 14 Jul 2011, 18:08

My IRQs can call in software interrupt but not working in hardware interrupt I used exactly same with this code. do you know why?

14 Jul 2011, 18:08

cod3b453

Joined: 25 Aug 2004
Posts: 618

cod3b453 22 Jul 2011, 19:15

ISRs require a valid GDT and IDT as well as interrupts being enabled. IRQs have an additional enable by writing 0 to their mask bit in their respective registers (Intel 8259 ports 0x20,0xA0) [writing 1 disables them].

Note the above code simply remaps the IRQs and disables (masks) them.

22 Jul 2011, 19:15

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 22 Jul 2011, 19:50

You also need to send a end of IRQ
Eg:

Code:

       mov  al,0x20
        out   0xa0,al
       out   0x20,al

At the end of every IRQ handler, or you will only get one firing, once.

22 Jul 2011, 19:50

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