Arria 10 IOPLL Dynamic Phase Shift using M-Counter

[FvM]

Hello,
we use to perform clock fine tuning with Cyclone designs by applying continuous phase shift  to M counter (PLL feedback clock divider). This way the frequency of all PLL output clocks is tuned by a proportional factor, similar to using a VCXO reference oscillator.

According to Arria 10 IOPLL documentation AN728, dynamic phase shift isn't provided for M-counter, so we would need cascaded PLLs to implement the intended tuning of multiple PLL outputs.

While testing an Arria 10 cascaded PLL design, I found that undocument value cntsel = 5'b01011 performs M-counter phase shift as available for Cyclone III, IV, 10 LP and MAX 10. 

Are there any reasons why the feature isn't documented?

Best regards

Frank

[Farabi]

Hi Frank,

Let me check with engineering on this. Did the phase shift you performed via M-counter is stable?

How long the PLL can get to Locked status after you performed the phase shift?

regards,

Farabi

[FvM]

Hi Farabi,
thanks for your interest.

PLL is staying locked after M-counter phase shift, Arria 10 IOPLL is behaving the same as Cyclone 10 LP which provides M-counter dynamic phase shift as documented feature.

Regards
Frank

[Farabi]

Hi Frank,

Noted. That is good info. I will update this to engineering.

regards,

Farabi