Two primary checks are setup and hold checks. Once a clock is defined at clock pin of a flip-flop (FF), setup and hold checks are automatically inferred for the FF. Timing checks are generally performed at multiple conditions including worst-case slow condition and best-case fast condition. Typically, worst-case slow condition is critical for setup check… read more »
In ECO period, there might be so-called ‘no-margin’ timing situation which means setup margin is not enough for fixing hold violation/add_buffer in the same reg2reg timing path, because besides OCV derating, check setup violation under slow corners and hold violation under fast corners, ratio of delay between SS and FF might be (2.5~3.5):1.
Sometimes, it is necessary to add constraint, such as set_disable_timing to let tool ignore timing path which should not be checked, critical path would be fixed by tool correctly. set_disable_timing -from in1 -to pass [get_cells dll/dll_delay_line_master/delay_0] set_disable_timing -from in1 -to pass [get_cells dll/dll_delay_line_clk_wr/delay_0] #ezp set_disable_timing -from in1 -to pass [get_cells dll_delay_line/delay_0] #ezp set_disable_timing -from in1… read more »
For chip tapeout, physical design must clean timing/skew/transition violations based on OCV (on chip variation) derating in signoff STA environment. http://www.techdesignforums.com/practice/guides/on-chip-variation-ocv/ For example, when check setup violation, launch path is late, clock cell delay times 1.039, data cell delay times 1.077, capture path is early, clock cell delay times 0.961, clock net delay times 0.915…. read more »
Pre CTS or placement, clock latency, skew, transition are considered as ideal zero, but tool add clock buffer/inverter in CTS period in order to minimums clock latency/skew/transition as much as possible, clock tree has insertion delay after CTS. Post CTS and post route, comparing to datapath delay change, clock path in launch path ‘stretch’, especially… read more »