IXP clock rate question

[Perry Wagle]

> Measurements with the microengine cycle counters suggest that the
> clock speed of our system is 177MHz as opposed to the manual's claim
> of 166MHz.
>
>  Does this sound accurate?

I'm including my own observations in my answer to your question:

I'm loading my boot loader from angel on a rev A board.  I have the
RTC firing an interrupt "once a second", and TIMER_1 firing "a hundred
times a second".  Angel has set the PLL_CFG register to (my debugging
routine dumps "label address value"):

	pll_cfg   90000c00 00000010

which I've assumed to be "correct", so haven't tried changing it,
especially since the documentation warns againts setting it too high.

The RTC uses what I call the "slow clock" (~ 3 MHz), and the TIMER's
use what I call the "fast clock" (~ 162 Mhz).

To initialize the RTC calibration, I set the RTC_DIV register to my
slow_clock (expressed in Hz) divided by 128, and currently get:

	rtc_div   90002000 00037080

(so RDIV = 0x7080) and to initialized the TIMER_1 calibration, I set
the TIMER_1_LOAD register to the my fast_clock (expressed in Hz)
divided by 100, and currently get:

	timer_1_load    42000300 0018bff0
	timer_1_control 42000308 000000c0

(notice that the value of timer_1_control shows that I am counting CPU
cycles without a divisor).

With my slow_clock constant set to 3686400 Hz and my fast_clock
constant set to 162200000, I am getting approximately 100.15 TIMER_1
interrupts per RTC interrupt (over a 12 hour period).  These two
values correspond to the ROUNDED values of the two clock rates from
page 28 of the "IXP1200 Network Processor Specification Update (June
2000)".  The roundoff is SIGNIFICANT to my measurement, and I wish the
documentation writers WOULDN'T ROUND OFF THE VALUES.  For example,
since the given value of the fast_clock was almost exactly 44 times
the given value of the slow_clock, I tried just setting the fast_clock
to exactly 44 times the slow clock, and got 100.5 TIMER_1 interrupts
per second.  BOTH values of the fast_clock were within the roundoff of
the value given in the documentation.

My setting of the slow_clock is consistant with the documentation's
suggestion, and the seconds doesn't skew according to my eyeball's
comparison with my wristwatch.  It's close enough that I'm not going
to worry more about it more until I have Linux running XNTP.

So my answer to your original question is that I'm somewhat confident
that I have the Core Clock measured at about 162 MHz (+- 1 Mhz), at
least with respect to the RTC and TIMER_1 hardware on Rev A hardware.
Which Rev do you guys have?

-- Perry