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Interrupt handling and routing: The Big Picture


Finally I stated to hack port-ofppc to support my Efika.
The Efika is a SBC based on the Freescale MPC5200 SOC with OpenFirmWare:

I have some prior experience in device driver hacking. I created a bus
attachment with its own bus_space(9) for the on chip bus. I can attach
ohci(4) to the build in USB host controller. There is still a strange
timeout in ohci_init() that I try to analize, but things look promising
for now.

Interrupts are next on the plan. The MPC5200 has its own, special
interrupt controller that is not compatible to any other interrupt
controller like OpenPIC. So everything in that area has to be coded new
from the ground up.

I tried to reverse engineer the existing code.
arch/powerpc/pci/pci_machdep_ofw.c:genofw_find_ofpics(), stuff in
arch/powerpc/pic/) But I am lost. I simply don't get The Big Picture
about how all this works and how different parts of the kernel
interact. (Is genofw_find_ofpics() only usable on PCI busses? Seems not
to me but it is located in pci_machdep_ofw.c) It would be a big help
for me if a PPC guru would explain the general concepts of interrupt
handling and routing in the NetBSD kernel in genral and in particular
for PPC ports. A rough guide about how to work on this and a roadmap
would be much appreciated.



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