Forum Discussion
Quartus reporting unconstrained inputs and outputs on constrained paths
Hi I have implemented a set of timing constraints on my Arria 10 design and I'm confused about two things. [Running Quartus Pro 22.1]
1. Quartus is reporting one of my input clocks (it is a differential clock, I'm not sure if this matters) as an unconstrained input port.
I have set the clock constraint as:
create_clock -name {chs_clk_rx} -period 150.000MHz [get_ports {chs_clk_rx}];
*I know the -period 150.000MHz is odd but the timing analyzer accepts it. I have additional input clock pins that are also differential signals that I set, for example:
create_clock -name {lvds_rx_1} -period 150.000MHz [get_ports {s1_lvds_in[1]}];
This signal does not show up as an unconstrained input port. Is there any reason why one might show up differently than the other?
2. I have a whole bunch of differential output signals where I have assigned an output delay constraint (or assigned a generated clock to output clocks) and the negative pin of the differential pair is showing up as unconstrained.
My understanding with differential pair timing constraints is we only constrain the positive edge so that the timing analyzer doesn't try to run two separate paths. Is this incorrect?
An example of the constraint in question:
create_generated_clock -name lvds_tx_1 -source [get_pins {i_pll_lvds|iopll_0|altera_iopll_i|twentynm_pll|iopll_inst|outclk[1]}] -master_clock [get_clocks {i_pll_lvds|iopll_0|outclk1}] -divide_by 1 -multiply_by 1 [get_ports {s1_lvds_out[1]}]
The positive pin is showing as constrained but the s1_lvds_out[1](n) is showing unconstrained.
Some advice would be greatly appreciated!
16 Replies
- Farabi_Altera
Regular Contributor
case re-assign to LVDS support engineer.
regards,
Farabi
- Nurina
Regular Contributor
Hello Tyler,
This case falls under LVDS area, so it has been reassigned to LVDS expert.
- AqidAyman_Altera
Regular Contributor
Hi Tyler,
I think it is better to share the .qar design for this project in order for us to further investigate this and if it is potentially a bug, we need it to report to the engineering team. You no need to share the full design, it is sufficient to share the one that related to this issue only for us to reproduce the issue from our end. You can share the file through email for privacy. I will initiate the email first.
Regards,
Aqid
- TMayd
Occasional Contributor
Hi Aqid,
Thank you. I have responded to your email.
Tyler
- MTw
New Contributor
Hello,
may I ask if there is any solution? I have the same issue with 4 differential outputs. Constaint like the other existing differential outputs but still shows up as unconstrained.
Please let me know if there is a solution to this case a year back...
Mirco