how to make PCI MSI working?

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marcrew
Posts: 7
Joined: Thu May 04, 2023 7:54 pm

how to make PCI MSI working?

Post by marcrew »

Hello everyone. I am a new beginner to OS developer. when I am developping my OS, I got issues which is ralated to MSI interrupt.

in my os, I disabled legacy PIC and enabled APIC, and I also added HPET timer. all these devices interrupts are working well through APIC. But when I am trying to add MSI , I cannot get it working.

according to chapter 6.8 of <PCI local bus sepecification 2.3> , I write 0xFEE00000(only 1 cpu used) to message address register, 0 to upper address(this device supports 64bits address). and then write 0x26(I want to use IRQ6) to message data. and then set bit 0 of message control. set Interrupt Disable of PCI cmd register at last. connect ISR to IRQ6. when the trigger happens, no ISR is called.

can you help me how to fix this issue? it would be a great appreciate to you.
Octocontrabass
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Re: how to make PCI MSI working?

Post by Octocontrabass »

marcrew wrote:I write 0xFEE00000(only 1 cpu used)
I'm not sure it's safe to assume the BSP APIC ID will always be 0. It probably will be, but you should still check.
marcrew wrote:0x26(I want to use IRQ6)
IRQ6 is an input to the legacy PIC and the IOAPIC. There's no such thing as IRQ6 when you're using MSIs.
marcrew wrote:set Interrupt Disable of PCI cmd register
What are the values of the other bits in the command register? You need to set the bus master bit to receive MSIs.
marcrew
Posts: 7
Joined: Thu May 04, 2023 7:54 pm

Re: how to make PCI MSI working?

Post by marcrew »

thanks for the reply.
Octocontrabass wrote:
marcrew wrote:I write 0xFEE00000(only 1 cpu used)
I'm not sure it's safe to assume the BSP APIC ID will always be 0. It probably will be, but you should still check.
I have checked the LAPIC ID , it is 0 .
marcrew wrote:0x26(I want to use IRQ6)
IRQ6 is an input to the legacy PIC and the IOAPIC. There's no such thing as IRQ6 when you're using MSIs.
OK, I connected vector 0x26(which is IRQ6 to PIC) to handler, then I wrote 0x26 to message data. is it the correct way?

marcrew wrote:set Interrupt Disable of PCI cmd register
What are the values of the other bits in the command register? You need to set the bus master bit to receive MSIs.
the CMD reg is 0x407, status reg is 0x10. it means bus master is set ,and legacy int is disabled ,right?
Octocontrabass
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Re: how to make PCI MSI working?

Post by Octocontrabass »

marcrew wrote:OK, I connected vector 0x26(which is IRQ6 to PIC) to handler, then I wrote 0x26 to message data. is it the correct way?
That's the correct value, but I still don't understand where you're getting IRQ6.
marcrew wrote:the CMD reg is 0x407, status reg is 0x10. it means bus master is set ,and legacy int is disabled ,right?
Right.
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