i.MX27 Clock sources

i.MX27 Clock sources

[Stuart Longland]

Hi all,
	Firstly, I'm new to this list, so hopefully this is not offtopic
-- if it is, I'm happy to be redirected.  I'm working on a device based
on the Freescale i.MX27 MCU; specifically, a Ka-Ro TX27-4030 module.
I'm using Ka-Ro's Linux kernel; although I'm looking into whether a port
of their patches to the current Linux kernel is feasible -- but that's
another story.

	For our application, it is necessary to interface this device to
a Texas Instruments TLV320AIC3204 CODEC.  The i.MX27 provides the clock
via SSI3_CLK, and communicates using I?S and I?C.  I understand that the
clock divider for the SSIs is driven from either MPLL or SPLL; but what
I'm not certain on is where those are configured in the Linux kernel, or
what the implications are for tinkering with these.

	Ideally I'd like to adjust MPLL/SPLL and/or the SSI clocks so
that the clock rate is some multiple of the I?S bit rate.  So far I can
get it close; but not close enough.  Does anyone have any pointers as to
where I can look in the Linux kernel for this information?

Regards,
-- 
Stuart Longland (aka Redhatter, VK4MSL)      .'''.
Gentoo Linux/MIPS Cobalt and Docs Developer  '.'` :
. . . . . . . . . . . . . . . . . . . . . .   .'.'
http://dev.gentoo.org/~redhatter             :.'

I haven't lost my mind...
  ...it's backed up on a tape somewhere.

i.MX27 Clock sources

[Lothar Waßmann]

Hi,

> 	For our application, it is necessary to interface this device to
> a Texas Instruments TLV320AIC3204 CODEC.  The i.MX27 provides the clock
> via SSI3_CLK, and communicates using I?S and I?C.  I understand that the
> clock divider for the SSIs is driven from either MPLL or SPLL; but what
> I'm not certain on is where those are configured in the Linux kernel, or
> what the implications are for tinkering with these.
> 
> 	Ideally I'd like to adjust MPLL/SPLL and/or the SSI clocks so
> that the clock rate is some multiple of the I?S bit rate.  So far I can
> get it close; but not close enough.  Does anyone have any pointers as to
> where I can look in the Linux kernel for this information?
> 
Can't you use the codec in master mode, instead of fiddling with the
CPU clocks?


Lothar Wa?mann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstra?e 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Gesch?ftsf?hrer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info at karo-electronics.de
___________________________________________________________

i.MX27 Clock sources

[Stuart Longland]

On Tue, May 18, 2010 at 11:04:01AM +0200, Lothar Wa?mann wrote:
> Hi,
> 
> > 	Ideally I'd like to adjust MPLL/SPLL and/or the SSI clocks so
> > that the clock rate is some multiple of the I?S bit rate.  So far I can
> > get it close; but not close enough.  Does anyone have any pointers as to
> > where I can look in the Linux kernel for this information?
> > 
> Can't you use the codec in master mode, instead of fiddling with the
> CPU clocks?

I think we will do this -- but the issue is still faced since the CODEC
derives its clocks from a clock supplied on a separate SSI bus.  (This
was done to avoid the need of a separate oscillator.)

I haven't succeeded in getting the CODEC's onboard PLL to generate the
required clocks either -- I'll be doing some further investigation on
this tomorrow.  However, the other way of achieving this is to tweak the
CPU to run its clocks at the required rate... and this is the other
possibility I'm exploring.

Regards,
-- 
Stuart Longland (aka Redhatter, VK4MSL)      .'''.
Gentoo Linux/MIPS Cobalt and Docs Developer  '.'` :
. . . . . . . . . . . . . . . . . . . . . .   .'.'
http://dev.gentoo.org/~redhatter             :.'

I haven't lost my mind...
  ...it's backed up on a tape somewhere.