Re: Question about e300 core decrementer interrupt

[Li Tao <b22598@freescale.com>]

Hi Scott Wood,
Thanks for your response

=E5=9C=A8 2009-09-09=E4=B8=89=E7=9A=84 13:43 -0500=EF=BC=8CScott Wood=E5=86=
=99=E9=81=93=EF=BC=9A
> On Wed, Sep 09, 2009 at 01:16:07PM +0200, Kenneth Johansson wrote:
> > On Tue, 2009-09-08 at 13:48 +0800, Li Tao-B22598 wrote:
> > > Dear all,
> > >=20
> > > I have a problem in MPC5121 sleep mode. As you know MPC5121 use e300c=
4
> > > core. When I make the e300c4 core into sleep mode, it will return to
> > > full power mode when the=E2=80=9Cdecrementer interrupt=E2=80=9D occur=
red.
> > >=20
> > > But in the e300 core reference manual said that the =E2=80=9Cdecremen=
ter
> > > interrupt=E2=80=9Dhave no effect when e300 core in sleep mode, becaus=
e the
> > > time
> > > base and decrementer are disabled while the core is in sleep mode.
> > > Can anybody explain about this procedure ?
>=20
> I'm not specifically familiar with MPC5121, but I'll answer from the
> perspective of MPC83xx which has a similar core:
>=20
> The decrementer stops ticking when the core goes to sleep.  However, if a
> decrementer was already pending (but masked with MSR[EE]) before you
> enter sleep mode, it will cause a wakeup.
>=20
> To avoid this, the decrementer is set to a very large value prior to and
> after disabling interrupts.  See generic_suspend_disable_irqs() in
> arch/powerpc/kernel/time.c.  Is this not happening for you?  Which kernel
> version are you using, and what mechanism are you using to go to sleep?
I use 2.6.24 kernel. The PM driver code have set decrementer to
0x7fffffff before go to sleep mode.
The driver set HID0[10]=3D1, then set MSR POW bit. PMCCR =3D 00111.
> =20
>=20
> > I'm a bit irritated that it's not as the "solution" can mean hardware
> > changes an thus it's potentially expensive.
>=20
> What sort of hardware changes?
>=20
> -Scott