Re: Q: IXP425 CPU (over) clock ?

Heinz Rohde a écrit :

I would say that the system is measuring against the RealTimeClock as an independant source.

BTW, how do you think the system is detecting speed? In my opinion, it has to count cycles and compare it with a reference souce, e.g. the RTC.

Am I wrong?

No you are right, but what if your RTC is using the same clock
source as your chip?

The IXP425 has internal timers, so if these are used to serve
as a reference for BogoMIPS for instance, they will be wrong
since their speed is derived from the external OSC. Cf section
2.1.14 of http://download.intel.com/design/network/datashts/25247905.pdf
which says:

The IXP42X product line and IXC1100 control plane processors
consists of four internal timers operating at 66.66 MHz
(which is 2 * OSC_IN input pin.) to allow task scheduling and
prevent software lock-ups. The device has four 32-bit counters:
Watch-Dog Timer Timestamp Timer Two general-purpose timers

If you want to be sure of what timer is used, take a look at the
Linux kernel source.


Laurent
.