[Gc-linux-devel] Interrupts on the GameCube

[Michael S. <mi...@c6...>]

Hi!

tmbinc and me have been talking about how to implement interrupts on=20
the GameCube. The GameCube has an interrupt controller with 14 sources.=20=

E=05ach source is a device, and each device can trigger one or more=20
different interrupts by only having one line to the interrupt=20
controller. This is quite similar to other architectures: Interrupt 8=20
in this case comes from the VI (Video Interface), and the VI has 4=20
different sources for interrupts.

The original GameCube system software  presents a linear system to the=20=

user. It is aware of all possible interrupts sources at the second=20
level and presents them in a single list. The user must only register=20
for one specific VI interrupt, for example, and not for the common VI=20
interrupt and then check which one it was, using the VI registers.=20
GCLIb also implements this behavior.

It is my understanding that it is common in Linux to only implement the=20=

first level in the kernel interrupt handling code, i.e. 14 sources, and=20=

that drivers must do the rest manually. This is done because the=20
generic kernel interrupt code cannot be aware of all different devices=20=

in a system - on a normal computer you can change the configuration=20
easily and remove or add devices, like PCI cards. On the GameCube, the=20=

number of different interrupts is fixed; there is no way to add a=20
device that can trigger another interrupt, so the generic interrupt=20
code would already handle all interrupts at the sources and pretend=20
that this two-level design didn't exist.

There are pros for each side. Presenting two levels is more the Linux=20
way, while linearizing the interrupts is easier for driver developers=20
and has no real disadvantages. I tend to prefer the Linux way, tmbinc=20
seems to prefer the GameCube SDK way.

What are your opinions?

   Michael=