Please help me with setup slack error

Thank you very much for your reply, kaz!

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I understand you have three ADC clocks each at 8MH

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This is exactly what I meant.

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create_clock -name {adc1_cout} -period 125.000 [get_ports {ADC1_COUT }]

create_clock -name {adc2_cout} -period 125.000 [get_ports {ADC2_COUT }]

create_clock -name {adc3_cout} -period 125.000 [get_ports {ADC3_COUT }]

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I am not convinced if three ADCs' output will come out at the same time, so this may produce better timing.

Also, I went through the AN433 and found a method using virtual clock to constrain the design(I will definitely split "adc_virt_cout" into three virtual clocks later. :) ):

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set_input_delay -add_delay -max -clock [get_clocks {adc_virt_cout}] 23.250 [get_ports {ADC1_DA[0]}]

set_input_delay -add_delay -min -clock [get_clocks {adc_virt_cout}] 2.000 [get_ports {ADC1_DA[0]}]

set_input_delay -add_delay -max -clock [get_clocks {adc_virt_cout}] 23.250 [get_ports {ADC1_DA[1]}]

set_input_delay -add_delay -min -clock [get_clocks {adc_virt_cout}] 2.000 [get_ports {ADC1_DA[1]}]

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This considers the setup and hold relationships are not the same as they are with respect to the input clock. The input data is edge-aligned with respect to the virtual clock. The hold

requirement with respect to the virtual clock must decrease by the amount of the shift

(period/4 for a center-aligned DDR interface). The setup requirement with respect to

the virtual clock must increase by the amount of the shift (period/4 for a

center-aligned DDR interface). The input maximum and minimum delay values both

decrease by the amount of the shift (period/4 for a center-aligned DDR interface).

the period here is 125ns, divided by 4 is 31.25ns. ADC data output have setup timing of 8ns, so the input maximum delay is 62.5 - 31.25 - 8 = 23.25ns. I reserve the hold timing of 2ns. This produce the follwing timing report:

https://www.alteraforum.com/forum/attachment.php?attachmentid=3904

The setup slack is 8.21ns. This slack should represent the estimation of setup time generated by TimeQuest. What brings the variation between the setup slack and ADC setup time?