My one-cent question

Hi all,

My "micro setup delay" is negative (-0.04). Why is it? Thanks a lot. Below is part of Classical Timing Report. It's true that fmax = 1/(tco + reg-to-reg-delay + tsu). tsu in the below report is negative. That's weird!!!

Thanks, guys.

Jeff

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Info: Slack time is -4.487 ns for clock "clk" between source register "int_input2[3]" and destination register "output[0]~reg0"

Info: Fmax is 182.25 MHz (period= 5.487 ns)

Info: + Largest register to register requirement is 0.736 ns

Info: + Setup relationship between source and destination is 1.000 ns

Info: + Latch edge is 1.000 ns

Info: Clock period of Destination clock "clk" is 1.000 ns with offset of 0.000 ns and duty cycle of 50

Info: Multicycle Setup factor for Destination register is 1

Info: - Launch edge is 0.000 ns

Info: Clock period of Source clock "clk" is 1.000 ns with offset of 0.000 ns and duty cycle of 50

Info: Multicycle Setup factor for Source register is 1

Info: + Largest clock skew is 0.000 ns

Info: + Shortest clock path from clock "clk" to destination register is 3.367 ns

Info: 1: + IC(0.000 ns) + CELL(1.100 ns) = 1.100 ns; Loc. = PIN_T2; Fanout = 1; CLK Node = 'clk'

Info: 2: + IC(0.135 ns) + CELL(0.000 ns) = 1.235 ns; Loc. = CLKCTRL_G3; Fanout = 35; COMB Node = 'clk~clkctrl'

Info: 3: + IC(1.466 ns) + CELL(0.666 ns) = 3.367 ns; Loc. = LCFF_X66_Y48_N13; Fanout = 1; REG Node = 'output[0]~reg0'

Info: Total cell delay = 1.766 ns ( 52.45 % )

Info: Total interconnect delay = 1.601 ns ( 47.55 % )

Info: - Longest clock path from clock "clk" to source register is 3.367 ns

Info: 1: + IC(0.000 ns) + CELL(1.100 ns) = 1.100 ns; Loc. = PIN_T2; Fanout = 1; CLK Node = 'clk'

Info: 2: + IC(0.135 ns) + CELL(0.000 ns) = 1.235 ns; Loc. = CLKCTRL_G3; Fanout = 35; COMB Node = 'clk~clkctrl'

Info: 3: + IC(1.466 ns) + CELL(0.666 ns) = 3.367 ns; Loc. = LCFF_X66_Y48_N11; Fanout = 3; REG Node = 'int_input2[3]'

Info: Total cell delay = 1.766 ns ( 52.45 % )

Info: Total interconnect delay = 1.601 ns ( 47.55 % )

Info: - Micro clock to output delay of source is 0.304 ns

Info: - Micro setup delay of destination is -0.040 ns

Info: - Longest register to register delay is 5.223 ns

Info: 1: + IC(0.000 ns) + CELL(0.000 ns) = 0.000 ns; Loc. = LCFF_X66_Y48_N11; Fanout = 3; REG Node = 'int_input2[3]'

Info: 2: + IC(1.128 ns) + CELL(0.596 ns) = 1.724 ns; Loc. = LCCOMB_X65_Y48_N6; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~215'

Info: 3: + IC(0.000 ns) + CELL(0.086 ns) = 1.810 ns; Loc. = LCCOMB_X65_Y48_N8; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~217'

Info: 4: + IC(0.000 ns) + CELL(0.086 ns) = 1.896 ns; Loc. = LCCOMB_X65_Y48_N10; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~219'

Info: 5: + IC(0.000 ns) + CELL(0.086 ns) = 1.982 ns; Loc. = LCCOMB_X65_Y48_N12; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~221'

Info: 6: + IC(0.000 ns) + CELL(0.190 ns) = 2.172 ns; Loc. = LCCOMB_X65_Y48_N14; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~223'

Info: 7: + IC(0.000 ns) + CELL(0.086 ns) = 2.258 ns; Loc. = LCCOMB_X65_Y48_N16; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~225'

Info: 8: + IC(0.000 ns) + CELL(0.086 ns) = 2.344 ns; Loc. = LCCOMB_X65_Y48_N18; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~227'

Info: 9: + IC(0.000 ns) + CELL(0.086 ns) = 2.430 ns; Loc. = LCCOMB_X65_Y48_N20; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~229'

Info: 10: + IC(0.000 ns) + CELL(0.086 ns) = 2.516 ns; Loc. = LCCOMB_X65_Y48_N22; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~231'

Info: 11: + IC(0.000 ns) + CELL(0.086 ns) = 2.602 ns; Loc. = LCCOMB_X65_Y48_N24; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~233'

Info: 12: + IC(0.000 ns) + CELL(0.086 ns) = 2.688 ns; Loc. = LCCOMB_X65_Y48_N26; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~235'

Info: 13: + IC(0.000 ns) + CELL(0.086 ns) = 2.774 ns; Loc. = LCCOMB_X65_Y48_N28; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~237'

Info: 14: + IC(0.000 ns) + CELL(0.506 ns) = 3.280 ns; Loc. = LCCOMB_X65_Y48_N30; Fanout = 1; COMB Node = 'Comparator_16bit:UT|LessThan1~238'

Info: 15: + IC(0.611 ns) + CELL(0.651 ns) = 4.542 ns; Loc. = LCCOMB_X66_Y48_N18; Fanout = 1; COMB Node = 'Comparator_16bit:UT|Mux0~66'

Info: 16: + IC(0.367 ns) + CELL(0.206 ns) = 5.115 ns; Loc. = LCCOMB_X66_Y48_N12; Fanout = 1; COMB Node = 'Comparator_16bit:UT|Mux0~67'

Info: 17: + IC(0.000 ns) + CELL(0.108 ns) = 5.223 ns; Loc. = LCFF_X66_Y48_N13; Fanout = 1; REG Node = 'output[0]~reg0'

Info: Total cell delay = 3.117 ns ( 59.68 % )

Info: Total interconnect delay = 2.106 ns ( 40.32 % )

Warning: Can't achieve timing requirement Clock Setup: 'clk' along 34 path(s). See Report window for details.