PCI questions

[nexos]

Hello,
I am currently making a PCI bus driver. I have a few questions however.
How do I read the PCI BARs? I know they are in the configuration space, but since they are DWORDs, how do read them.
How do I figure out what IO APIC line INTA, INTB, INTC, and INTD are without ACPI?
Do I need to enable PCI IRQs explicitly? If so, how do you do it?
And lastly, how do you work with the PCI Busmastering DMA?
Thanks,
nexos

[bellezzasolo]

Hello,
I am currently making a PCI bus driver. I have a few questions however.
How do I read the PCI BARs? I know they are in the configuration space, but since they are DWORDs, how do read them.
How do I figure out what IO APIC line INTA, INTB, INTC, and INTD are without ACPI?
Do I need to enable PCI IRQs explicitly? If so, how do you do it?
And lastly, how do you work with the PCI Busmastering DMA?
Thanks,
nexos

For BARs - Read configuration space as a DWORD.

Figuring out IO APIC lines without ACPI? Basically, you don't. You need an AML interpreter to get the correct mappings.
Or, you take my approach, and just use MSI(X) instead

For IRQs, you need to unmask bit 10 of Command/Status to enable pinned interrupts. For MSI, it's a bit of the MSI control register.
Set Bits 1 and 2 of Command/Status to enable memory access and bus mastering.

My PCI(E) code

[iansjack]

How do I read the PCI BARs? I know they are in the configuration space, but since they are DWORDs, how do read them.

I'm not sure that I understand your problem. You just do a dword "in" to %eax.

[Octocontrabass]

How do I figure out what IO APIC line INTA, INTB, INTC, and INTD are without ACPI?

On ancient hardware (and VMs that can run OSes that work on ancient hardware) you can use the MP tables.

[nexos]

Thanks for your answers. I now have an understanding of PCI and have decided to use MSI in my Operating System.

[nexos]

I have managed to make the PCI bus driver, but what is a simple PCI device I can program to test stuff like IRQs, BAR mapping, MSI, and Busmastering?

[bellezzasolo]

I have managed to make the PCI bus driver, but what is a simple PCI device I can program to test stuff like IRQs, BAR mapping, MSI, and Busmastering?

Dare I say it, xHCI?

Not simple by any means, but it's not hard to test the IRQs and such. A "simple" device descriptor request tests bus mastering.

I'm currently working on an i219[v] driver, because I figure that'll be simpler than implementing a full USB stack for keyboard support, but I haven't tested bus mastering yet. BAR mapping and MSI work though.

[nexos]

So in my BAR obtaining code, it appears that MMIO and IO Space regions are backwards. MMIO regions are set to be IO space and regions, and vice versa. The code that figures whether the BAR represents MMIO looks like this

Code: Select all

INT isMmio = !barLow & 1;

Is that correct?

[thewrongchristian]

So in my BAR obtaining code, it appears that MMIO and IO Space regions are backwards. MMIO regions are set to be IO space and regions, and vice versa. The code that figures whether the BAR represents MMIO looks like this

Code: Select all

INT isMmio = !barLow & 1;

Is that correct?

The lowest bit of the BAR is 1 if this is an IO address space BAR.

Your code looks like it should work, if barLow is a MMIO address, its LSB will be 0, !barLow LSB will be 1, and so isMmio will be non-zero (true). Have you inverted the test later on by accident?

I would find this test easier, though in the form:

Code: Select all

bool isMmio = (0==(barLow & 1)); 

[nexos]

I have finished my PCI host controller driver. Thanks for all your help during its development.
nexos

[Octocontrabass]

Code: Select all

INT isMmio = !barLow & 1;

Is that correct?

You forgot parentheses.

Code: Select all

INT isMmio = !(barLow & 1);