[U-Boot-Users] [PATCH 4/6] TQM885D: use calculated cpuclk instead of measuring it

[Martin Krause]

wd at denx.de wrote on Friday, October 05, 2007 1:10 PM:
> In message <11915787621757-git-send-email-martin.krause at tqs.de> you
> wrote: 
> > On the TQM885D the measurement of cpuclk with the PIT reference
> > timer ist not necessary. Since all module variants use the same
> 
> Ummm.. it may not be strictly necessary - but does it hurt? Or is it
> not working?

To make it work, changes in /cpu/mpc8xx/speed.c would be necessary. I
send a patch some weeks ago ("TQM885D: Use the OSCM,feeded by EXTAL =
 10 MHz"), which wasn't accepted, because board specific code is
not allowed in this file.

> > external 10 MHz oscillator, the cpuclk only depends on the PLL
> > configuration - which is readable by software.
> 
> If it's working as expected, I recommend to leave the measurement as
> is - it allows for example to easily detect clocking problems for
> example because of a broken or wrong quartz.

Since we only have one quartz on the TQM885D, we could not do 
reference measurements like on the other TQM8xx boards (which have
two independent external clock sources). So Measuring the clock with
the PIT will produce the same result as calculating the clock from 
the PLL register values.

Another point is, that older TQM885D boards use EXTCLK as clock
source and newer versions EXTAL. If the cpuclk is calculated,
the same u-boot Image could be used for the older and the newer
board versions. If cpuclk is measured two different U-Boot images
would be necessary.

Best Regards,
Martin Krause