how to fix fanout and transition violations in DC

[tozibam]

Hi,

In my dctcl file, the constraints for reset are as followings:

set_drive 0 [find port rstb]
set_dont_touch_network [find port rstb]
set_resistance 0 [find net rstb]
set_ideal_net [find net rstb]

In vhdl file, a net connected to the reset of 256 registers is designed as:

reg_clr <= '0' when new_iv='1' else rstb

Since reset is set as don't touch, DC cannot optimize the reg_clr.

I have set the max fanout to be 15 so there is the violation.

There are also max_transition violations probably caused by high fanout network. It is shown as follows:

max_transition

Required Actual
Net Transition Transition Slack
-----------------------------------------------------------------
reg_clr (dont_touch) 1.50 8.91 -7.41 (VIOLATED)
PIN : s2_0/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_1/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_2/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_3/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_4/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_5/data_reg_reg/RB
1.50 8.91 -7.41 (VIOLATED)
PIN : s2_6/data_reg_reg/RB


Could anyone teach me how to optimize this type of network? It is conneted to reset via a combinational logic and I cannot use set_drive 0.

Thanks.

 

[rca]

Without floorplan, it is not relevant to fix DRV (trans/cap) during the synthesis step.
This must be done during the PnR.