KVM's PIT and PIC programming question

KVM's PIT and PIC programming question

[Saksena, Abhishek]

Hi Guys,
I am writing very simple bios for KVM (not using Qemu but creating a simple io device models around KVM). I am having trouble in receiving regular Timer interrupts after programming PIT.

I think I have enabled PIC and PIT correctly using following code:-

PIC Programming 
;; PIC
  mov  al, #0x00
  out  0x21, AL ;master pic: all IRQs unmasked
  out  0xA1, AL ;slave  pic: all IRQs unmasked


PIT Programming 

and also enable PIT to genrate regular timer interruput

SET_INT_VECTOR(0x08, #0xF000, #int08_handler)
  mov al, #0x34 ; timer0: binary count, 16bit count, mode 2
  out 0x43, al
  mov al, #0x00 ; maximum count of 0000H = 18.2Hz
  out 0x40, al
  out 0x40, al


PIT Timer ISR code

Timer ISR code

;---------
;- INT08 -
;---------
.org 0xfea5 ; INT 08h System Timer ISR Entry Point
int08_handler:
  sti
  push ax
  push ds
  mov ax, #0x0040
  mov ds, ax
  mov ax, 0x006c ; increment lower word
  inc ax
  mov 0x006c, ax
  jnz inc_done
  mov ax, 0x006e ; increment upper word
  inc ax
  mov 0x006e, ax



For some reason I never see int08_handler ever been called. Any clues what may be wrong? I am creating only one VCPU


-Abhishek

Re: KVM's PIT and PIC programming question

[Avi Kivity]

On 08/20/2009 12:26 AM, Saksena, Abhishek wrote:
> Hi Guys,
> I am writing very simple bios for KVM (not using Qemu but creating a simple io device models around KVM). I am having trouble in receiving regular Timer interrupts after programming PIT.
>
> I think I have enabled PIC and PIT correctly using following code:-
>
> PIC Programming
> ;; PIC
>    mov  al, #0x00
>    out  0x21, AL ;master pic: all IRQs unmasked
>    out  0xA1, AL ;slave  pic: all IRQs unmasked
>
>
> PIT Programming
>
> and also enable PIT to genrate regular timer interruput
>
> SET_INT_VECTOR(0x08, #0xF000, #int08_handler)
>    mov al, #0x34 ; timer0: binary count, 16bit count, mode 2
>    out 0x43, al
>    mov al, #0x00 ; maximum count of 0000H = 18.2Hz
>    out 0x40, al
>    out 0x40, al
>
>
> PIT Timer ISR code
>
> Timer ISR code
>
> ;---------
> ;- INT08 -
> ;---------
> .org 0xfea5 ; INT 08h System Timer ISR Entry Point
> int08_handler:
>    sti
>    push ax
>    push ds
>    mov ax, #0x0040
>    mov ds, ax
>    mov ax, 0x006c ; increment lower word
>    inc ax
>    mov 0x006c, ax
>    jnz inc_done
>    mov ax, 0x006e ; increment upper word
>    inc ax
>    mov 0x006e, ax
>
>
>
> For some reason I never see int08_handler ever been called. Any clues what may be wrong? I am creating only one VCPU
>
>
>    

Things to check:

- have you initialized the kernel PIC and PIT?
- are interrupts enabled?

-- 
error compiling committee.c: too many arguments to function

RE: KVM's PIT and PIC programming question

[Saksena, Abhishek]

Isn't by default PIT and PIC are initialized in Kernel? Is something more needed on top of it?

I have enable PIC interuupt using following code :-

> PIC Programming
> ;; PIC
>    mov  al, #0x00
>    out  0x21, AL ;master pic: all IRQs unmasked
>    out  0xA1, AL ;slave  pic: all IRQs unmasked


Also, I wonder if LAPIC need to be configured and initialized properly. I don't want to use LAPIC, can it be disabled in KVM. I am just using one VCPU.

-Thanks
Abhishek

 

-----Original Message-----
From: Avi Kivity [mailto:avi@redhat.com] 
Sent: Thursday, August 20, 2009 1:29 AM
To: Saksena, Abhishek
Cc: kvm@vger.kernel.org
Subject: Re: KVM's PIT and PIC programming question

On 08/20/2009 12:26 AM, Saksena, Abhishek wrote:
> Hi Guys,
> I am writing very simple bios for KVM (not using Qemu but creating a simple io device models around KVM). I am having trouble in receiving regular Timer interrupts after programming PIT.
>
> I think I have enabled PIC and PIT correctly using following code:-
>
> PIC Programming
> ;; PIC
>    mov  al, #0x00
>    out  0x21, AL ;master pic: all IRQs unmasked
>    out  0xA1, AL ;slave  pic: all IRQs unmasked
>
>
> PIT Programming
>
> and also enable PIT to genrate regular timer interruput
>
> SET_INT_VECTOR(0x08, #0xF000, #int08_handler)
>    mov al, #0x34 ; timer0: binary count, 16bit count, mode 2
>    out 0x43, al
>    mov al, #0x00 ; maximum count of 0000H = 18.2Hz
>    out 0x40, al
>    out 0x40, al
>
>
> PIT Timer ISR code
>
> Timer ISR code
>
> ;---------
> ;- INT08 -
> ;---------
> .org 0xfea5 ; INT 08h System Timer ISR Entry Point
> int08_handler:
>    sti
>    push ax
>    push ds
>    mov ax, #0x0040
>    mov ds, ax
>    mov ax, 0x006c ; increment lower word
>    inc ax
>    mov 0x006c, ax
>    jnz inc_done
>    mov ax, 0x006e ; increment upper word
>    inc ax
>    mov 0x006e, ax
>
>
>
> For some reason I never see int08_handler ever been called. Any clues what may be wrong? I am creating only one VCPU
>
>
>    

Things to check:

- have you initialized the kernel PIC and PIT?
- are interrupts enabled?

-- 
error compiling committee.c: too many arguments to function

Re: KVM's PIT and PIC programming question

[Avi Kivity]

On 08/20/2009 06:05 PM, Saksena, Abhishek wrote:
> Isn't by default PIT and PIC are initialized in Kernel? Is something more needed on top of it?
>
>    

You need KVM_CREATE_IRQCHIP and KVM_CREATE_PIT.

> Also, I wonder if LAPIC need to be configured and initialized properly. I don't want to use LAPIC, can it be disabled in KVM. I am just using one VCPU.
>    

The lapic is disabled by default.

-- 
error compiling committee.c: too many arguments to function

RE: KVM's PIT and PIC programming question

[Saksena, Abhishek]

I am using libkvm and believe it creates PIC and PIT by default.

I see kvm_create make calls to:- 

1. kvm_arch_create function which indeed calls kvm_create_pit and KVM_CREATE_PIT

2. kvm_create_irqchip function and KVM_CREATE_IRQCHIP


Is this understanding wrong?


-Thanks
Abhishek

-----Original Message-----
From: Avi Kivity [mailto:avi@redhat.com] 
Sent: Thursday, August 20, 2009 8:21 AM
To: Saksena, Abhishek
Cc: kvm@vger.kernel.org
Subject: Re: KVM's PIT and PIC programming question

On 08/20/2009 06:05 PM, Saksena, Abhishek wrote:
> Isn't by default PIT and PIC are initialized in Kernel? Is something more needed on top of it?
>
>    

You need KVM_CREATE_IRQCHIP and KVM_CREATE_PIT.

> Also, I wonder if LAPIC need to be configured and initialized properly. I don't want to use LAPIC, can it be disabled in KVM. I am just using one VCPU.
>    

The lapic is disabled by default.

-- 
error compiling committee.c: too many arguments to function

Re: KVM's PIT and PIC programming question

[Avi Kivity]

On 08/20/2009 07:49 PM, Saksena, Abhishek wrote:
> I am using libkvm and believe it creates PIC and PIT by default.
>
> I see kvm_create make calls to:-
>
> 1. kvm_arch_create function which indeed calls kvm_create_pit and KVM_CREATE_PIT
>
> 2. kvm_create_irqchip function and KVM_CREATE_IRQCHIP
>    

It should work, but best to check using strace or adding printfs.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

RE: KVM's PIT and PIC programming question

[Saksena, Abhishek]

Thnaks,

So just programming of PIC (8259) should do the trick. Do I have to care about IOAPIC or LAPIC programming? You mentioned lapic is disabled by default, what about IOAPIC. 


I see in x86.c

case KVM_CREATE_IRQCHIP:
		r = -ENOMEM;
		kvm->arch.vpic = kvm_create_pic(kvm);
		if (kvm->arch.vpic) {
			r = kvm_ioapic_init(kvm);
			if (r) {
				kfree(kvm->arch.vpic);
				kvm->arch.vpic = NULL;
				goto out;
			}
		} else
			goto out;
		break;


so ioapic is created.



I have enabled all the interrupts in 8259s correctly


PIC Programming of master and slave 8259s
;; PIC
    mov  al, #0x00
    out  0x21, AL ;master pic: all IRQs unmasked
    out  0xA1, AL ;slave  pic: all IRQs unmasked


 PIT Programming

 SET_INT_VECTOR(0x08, #0xF000, #int08_handler)
    mov al, #0x34 ; timer0: binary count, 16bit count, mode 2
    out 0x43, al
    mov al, #0x00 ; maximum count of 0000H = 18.2Hz
    out 0x40, al
    out 0x40, al

But still not see PIT interrupts or Timer ISR being called!


-thanks
Abhishek


-----Original Message-----
From: Avi Kivity [mailto:avi@redhat.com] 
Sent: Thursday, August 20, 2009 10:26 AM
To: Saksena, Abhishek
Cc: kvm@vger.kernel.org
Subject: Re: KVM's PIT and PIC programming question

On 08/20/2009 07:49 PM, Saksena, Abhishek wrote:
> I am using libkvm and believe it creates PIC and PIT by default.
>
> I see kvm_create make calls to:-
>
> 1. kvm_arch_create function which indeed calls kvm_create_pit and KVM_CREATE_PIT
>
> 2. kvm_create_irqchip function and KVM_CREATE_IRQCHIP
>    

It should work, but best to check using strace or adding printfs.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

Re: KVM's PIT and PIC programming question

[Avi Kivity]

On 08/20/2009 08:36 PM, Saksena, Abhishek wrote:
> Thnaks,
>
> So just programming of PIC (8259) should do the trick. Do I have to care about IOAPIC or LAPIC programming? You mentioned lapic is disabled by default, what about IOAPIC.
>
>    

The ioapic will not have any vectors programmed so it will do nothing.


> I see in x86.c
>
> case KVM_CREATE_IRQCHIP:
> 		r = -ENOMEM;
> 		kvm->arch.vpic = kvm_create_pic(kvm);
> 		if (kvm->arch.vpic) {
> 			r = kvm_ioapic_init(kvm);
> 			if (r) {
> 				kfree(kvm->arch.vpic);
> 				kvm->arch.vpic = NULL;
> 				goto out;
> 			}
> 		} else
> 			goto out;
> 		break;
>
>
> so ioapic is created.
>
>
>
> I have enabled all the interrupts in 8259s correctly
>
>
> PIC Programming of master and slave 8259s
> ;; PIC
>      mov  al, #0x00
>      out  0x21, AL ;master pic: all IRQs unmasked
>      out  0xA1, AL ;slave  pic: all IRQs unmasked
>
>
>   PIT Programming
>
>   SET_INT_VECTOR(0x08, #0xF000, #int08_handler)
>      mov al, #0x34 ; timer0: binary count, 16bit count, mode 2
>      out 0x43, al
>      mov al, #0x00 ; maximum count of 0000H = 18.2Hz
>      out 0x40, al
>      out 0x40, al
>
> But still not see PIT interrupts or Timer ISR being called!
>
>    

I suggest adding printk()s (or trace_printk()s) in stragtegic places to 
see what's going on.  It can be either a guest programming error or host 
bug.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.