2633 - How to use PAR_ADJ with FREQUENCY and set the ratio between the clock domains? 

2633 - How to use PAR_ADJ with FREQUENCY and set the ratio between the clock domains? 

PAR_ADJ allows you to loosen requirements for PAR results while tightening up the requirements reported by the timing analysis tool. The variance in required timing values on PAR and TRACE enables you to experiment more efficiently with the strategy of purposely over constraining your design to determine your best constraint settings. For example, if FREQUENCY is set to 250MHz and you set PAR_ADJ to 20, the software will use the simple additions formula of 250 + 20 = 270MHz to direct PAR while running TRACE on 250MHz. When paths cross two clock domains, if only FREQUENCY is specified, then the cross domain paths will be constrainted to be the fastest clock frequency. To do it right, for the crossed domain clocks, adjust to the same ratio, so that the PAR adjusted clock will maintain the same ratio. For example: FREQUENCY NET "clk1_c" 100 MHz PAR_ADJ 10; FREQUENCY NET "clk2_c" 50 MHz PAR_ADJ 5;