Re: Interrupts on the GameCube

Hi !

I don't want to say stupid things, but IIRC the Linux kernel can handle 
an Interrupt quickly (first level) but can report its treatment later 
(second level) to improve the speed/latency, can not do it !?
If so, it should be better to use the Linux way...

Free The Cube.


Michael Steil wrote:
> 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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