[LinuxBIOS] Building an irq table - Help

Marc Jones marc.jones at amd.com
Fri Oct 19 17:53:56 CEST 2007

joe at smittys.pointclark.net wrote:
> Quoting Marc Jones <marc.jones at amd.com>:
>> joe at smittys.pointclark.net wrote:
>>> Ok I am a little confused on how to tell what devices are what in  
>>> irc_tablec.c
>>> How do I tell?? Also where does the value for the "bitmap" come from?
>>> Thanks for your help - Joe
>>> /* bus,     dev|fn,
>>> {0x01,(0x08<<3)|0x0,
>>> {0x00,(0x1f<<3)|0x0,

>>> {0x00,(0x02<<3)|0x0,
>> Joe,
>> There is some good information here:
>> http://linuxbios.org/index.php/Creating_Valid_IRQ_Tables
>> http://www.microsoft.com/whdc/archive/pciirq.mspx
>> Your bus/dv/fun should match the devices found when you do an lspci.
>> The value for the bitmap is what IRQs are available on that INT#.
>> Theses are typically 10 and/or 11 but could be any shareable IRQ.
>> Marc
>> DDDD is PCI DEV, FFFF is function, LNK is PCI link - so LNKA B etc...
>> Next parameter is 00 if you do not support legacy PIC routing at all.
>> Last parameter is global interrupt NR.
>> Hope it helps,
>> Rudolf
> Thanks for your help Marc and Rudolf. I have been looking through most 
> of the other irq_tables.c from different mainboards and it seems like on 
> most of them the "fn" is 0x0 (like above). Is this a bug in getpir?? So 
> do I need to manually change these to the correct functions?
> I understand where the "link" comes from. These are set in the LPC 
> Bridge registers, but where does the value for the "bitmap" come from? 
> Mine eithor say 0xded8 or 0x0000?? The 0x0000 means it is not routed 
> right? But I don't get where the 0xded8 comes from?
> I just attached my irq_tables.c created from getpir so you can see what 
> I mean.
> Thanks - Joe

The bitmap is means for every bit that is set can be routed as an IRQ. 
So, bit 10 and 11 set means that link can be programmed to IRQ 10 or 11. 
The bitmap would be 0x0c00.

0xded8 = 1101111011011000
          |          ||_IRQ3
          |          |__IRQ4


Marc Jones
Senior Firmware Engineer
(970) 226-9684 Office
mailto:Marc.Jones at amd.com

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