Interrupts on the GameCube

Hi!

tmbinc and me have been talking about how to implement interrupts on 
the GameCube. The GameCube has an interrupt controller with 14 sources. 
Each source is a device, and each device can trigger one or more 
different interrupts by only having one line to the interrupt 
controller. This is quite similar to other architectures: Interrupt 8 
in this case comes from the VI (Video Interface), and the VI has 4 
different sources for interrupts.

The original GameCube system software  presents a linear system to the 
user. It is aware of all possible interrupts sources at the second 
level and presents them in a single list. The user must only register 
for one specific VI interrupt, for example, and not for the common VI 
interrupt and then check which one it was, using the VI registers. 
GCLIb also implements this behavior.

It is my understanding that it is common in Linux to only implement the 
first level in the kernel interrupt handling code, i.e. 14 sources, and 
that drivers must do the rest manually. This is done because the 
generic kernel interrupt code cannot be aware of all different devices 
in a system - on a normal computer you can change the configuration 
easily and remove or add devices, like PCI cards. On the GameCube, the 
number of different interrupts is fixed; there is no way to add a 
device that can trigger another interrupt, so the generic interrupt 
code would already handle all interrupts at the sources and pretend 
that this two-level design didn't exist.

There are pros for each side. Presenting two levels is more the Linux 
way, while linearizing the interrupts is easier for driver developers 
and has no real disadvantages. I tend to prefer the Linux way, tmbinc 
seems to prefer the GameCube SDK way.

What are your opinions?

   Michael


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