Re: [Linuxptp-users] recvmsg tx timestamp failed: Resource temporarily unavailable

[Rayagond K. <ray...@gm...>]

On 9 February 2013 17:21, Richard Cochran <ric...@gm...> wrote:

> On Sat, Feb 09, 2013 at 04:13:08PM +0530, Rayagond Kokatanur wrote:
> >
> > What is max_adj value ? Is it a maximum clock frequency connect to my
> > MAC/PTP ?
>
> No.
>
> It is maximum adjustment (in parts per billion) tolerated by your
> clock. If your clock can accept an adjustment 0.1%, then max_adj
> will be 1000000.
>

okay, I will check with HW team and assign correct value.


>
> > Whenever ptp4l calls .adjfreq, it passes either +/1 .max_adj frequency to
> > .adjfreq api, why ?
>
> Because the servo is trying to steer the clock at the maximum possible
> rate. Probably your time stamps are messed up.
>

So once SLAVE sync to MASTER then ptp stack should not call .adjfreq api
right, unless there is change in MASTER time.


> > 2> DEFAULT_ADDEND = 0xF0000029
> >
> > What is this magic number ?
>
> The ixp featues a frequency compenstated clock, with input clock at
> 66 MHz. Every input clock, the addend is accumulated into a 32 bit
> register. When that register overflows, it produces one clock tick at
> the nominal frequency of 62.5 MHz. Changing the addend makes the clock
> go faster or slower.
>

But how 0xF0000029 value wrt 66MHz clock ?

In our device the way driver need to update the ADDEND registers is same as
ixp device ie (2^32)/freq_ratio, where freq_ratio = ptp_clock_freq/50000000.

So in my case ptp clock freq or system clock freq is 62.5MHz, so DEFAULT
value i am taking is = ((2^32) * 50000000)/62500000 = 0xCCCCCC.

Is my default addend value correct ?


> > Is it calculated based on max_adj frequency
> > value ?
>
> No, it is the other way round.
>
> HTH,
> Richard
>


Thanks and Regards
Rayagond