Re: [Linuxptp-users] Issue with initial high jitter(Path Delay Variation)

[Richard C. <ric...@gm...>]

Wow, your code is totally broken...

On Thu, Feb 18, 2016 at 12:04:22PM +0530, Sujatha Guguloth wrote:
> static int xlnx_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
> {
>         struct xlnx_ptp_timer *timer = container_of(ptp, struct
> xlnx_ptp_timer,
>                                               ptp_clock_info);
> 
>         int neg_adj = 0;
>         u64 freq = 0;
>         u32 diff = 0;
>         u32 incval = 0;
> 
>         /* External clock source Frequency is 200MHz    which is driving
> the timer  */
>         /* adjust the RTC Increment Control register by (1/200MHZ = 5ns)  */
>         /* resolution of the increment register is 1/1048576              */
>         /* hence 5 * 1048576 = 0x500000 - value to be written to the
> register */
>         incval = 0x500000;
> 
>         if (ppb < 0) {
>           neg_adj = 1;
>           ppb = -ppb;
>         }
> 
>         freq = incval;
>         freq *= ppb;
>         diff = div_u64(freq, 1000000000ULL);
> 
>         incval = neg_adj ? (incval - diff) : (incval + diff);
> 
>         /* Write the adjusted value to the *RTC Increment Value Control
> Register* */
>         /* Writing the adjustment value to this register intern adjusts the
> nanoseconds register value by the hw */

You calculate 'incval' and then do nothing with it.
 
>         return 0;
> }
> 
> 
> static int xlnx_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
> {
>         unsigned long flags = 0;
>         struct xlnx_ptp_timer *timer = container_of(ptp, struct
> xlnx_ptp_timer,
>                                               ptp_clock_info);
>         struct timespec offset, then = ns_to_timespec(delta);
> 
>         spin_lock_irqsave(&timer->reg_lock, flags);
> 
>         /* Read the seconds and nano seconds from the RTC Seconds and RTC
> Nano Seconds Registers */
>         xlnx_rtc_offset_read(timer, &offset);
> 
>         /* set the current offset values */
>         offset = then;

You are supposed to add the delta.
 
>         /* Write the seconds and nano seconds to the *RTC Seconds* and *RTC
> Nano Seconds* Registers */
>         xlnx_rtc_offset_write(timer, (const struct timespec *)&offset);
> 
>         spin_unlock_irqrestore(&timer->reg_lock, flags);
>         return 0;
> }

Good luck,
Richard