Hold violation and PLL

[a2zasics]

Hi,
I have a problem on quartus II 3.0 software. I am using enhanced PLL
and a set of input registers with FAST INPUT REG = on constraint. Thus
i get about 1 ns delay of pad to IOB flop on datapath. However delay
of clock from PLL to IOB flops is higher around 3 ns. Thus i get a
hold violation of 2 ns. Anyone has any suggestions as to how i can
eliminate this hold violation.

Shardendu

 

[Muthu]

Hi,

I think Quartus software, is for Altera FPGAs... I haven't used Altera
FPGAs.

But in general i can give some options.

1. Try to pack the First Flip Flop in to IOBs.. This option is
available in Xilinx. I don't know about Altera.
2. Make the data path pad property to SLOW
3. Adjust the phase shift of PLL.. ie., delay it to caputre data in
next clock cycle
4. Else put some additonal dealy in the data path


Regards,
Muthu

shardendu@verizon.net (a2zasics) wrote in message news:<1c97c9ba.0312032206.3000a8e7@posting.google.com>...

Hi,
I have a problem on quartus II 3.0 software. I am using enhanced PLL
and a set of input registers with FAST INPUT REG = on constraint. Thus
i get about 1 ns delay of pad to IOB flop on datapath. However delay
of clock from PLL to IOB flops is higher around 3 ns. Thus i get a
hold violation of 2 ns. Anyone has any suggestions as to how i can
eliminate this hold violation.

Shardendu

 

[Mike Treseler]

a2zasics wrote:

hold violation of 2 ns. Anyone has any suggestions as to how i can
eliminate this hold violation.

What happens if you remove the constraint?

-- Mike Treseler