[Cbe-oss-dev] Fwd: adding virtual SPU timers

[Arnd Bergmann]

On Monday 22 October 2007, Uzi Shvadron wrote:

> > On Monday 15 October 2007, Arnd Bergmann wrote:
> > >
> > > Also, I'd like to hear what kind of requirement other people
> > > have so we can do the right thing and don't need another special
> > > workaround for a specific use of the timers.
>
> The SPU time base should be a system resource as the PPE time base is. That
> is, it should run freely and be accessed by an API such as the spu-timer
> API.
> In order to provide a time value the spu-timer should always be active and
> provide a 64 bits increment clock. This comes along with another idea to
> provide a small service kernel on the SPUs. This kernel may provide a set
> of services and environment variables to the applications. One of these
> services would be the spu-timer API. I know this opens the stage to larger
> discussion and there is a need to defined set of requirements. Note though
> that the above issues may lead to such solution. If such a kernel is
> created there will be no need to deal with the timer at the Linux kernel
> level.

I don't think we can get to the point where everybody agrees on a
common runtime environment beyond what is provided with libc, but it sounds
fair to have an (optional) library abstracts the use of the decrementer
in the same way that we have libraries for managing overlays and MFC tags.

The way you describe where you want to end up sounds like it would conflict
with Dean's work, as it suggests that that there needs to be a source for
real time instead of the 'virtual time' that Dean was asking for.

	Arnd <><