( ESNUG 279 Item 4 ) ------------------------------------------------ [2/5/98]
From: Srikant-reddy.MODUGULA@st.com (Srikant R Modugula)
Subject: Identifying Clock Trees As "Clock" Startpoints In Prime/DesignTime
Hi John,
Here is something which I have asked Synopsys for and want to share with
other users. I wish Synopsys provides the feature soon. Design:
_________
| |
| _____ |
| | DFF |_|__ NET_A
----|>|_____| | |
CLK_A | | |
|_________| |
Block "A" | _______
| NET_C | |
| ->-| |
| | | |
| | | |
| | |_______|
| _______________ | Block "C"
| | _______ | |
|->-|-| Comb. |_ | |
| | Logic | | | |
| |_______| |->-|->-|
| _____ | |
CLK_B | | DFF |___| |
----|>|_____| |
|_______________|
Block "B"
Premises:
1/ CLK_A and CLK_B are derived from SAME clock "phi" thru a clock-tree
network.
2/ Between CLK_B and "DFF" there is another clock-tree.
3/ The path "CLK_A - NET_A - NET_C" is longer than "CLK_B - NET_C"
4/ I dont (want to) know the instance names of "DFF" in Blocks A/B
Problem: Now I want to report_timing, from "CLK_B - NET_C" ?
I try :
report_timing -del max -from CLK_B -thr NET_C
--> no paths since the path starts at "clock pin" of "DFF";
not from CLK_B
report_timing -del max -from phi -thr NET_C
--> gives path from "CLK_A - NET_A - NET_C" since it is longer.
How can i pin point this path, using a report_timing command?
Now, the only (brutal!) way I found to get the path from "CLK_B to
NET_C" is to use report_timing -del max -max 100 -from phi -thr NET_C
--> hoping that "CLK_B - NET_C" is in those 100 paths I do text
processing to get that path.
Note that the "clock tree" from "phi" to "CLK_B's DFF" is understood
by DC/PTime with set_clock_skew -propagated command and this insertion
delay is considered while reporting paths from "CLK_B's DFF"! DC/PTime has
the information; it now needs to use it for understanding the command:
report_timing -del max -from CLK_B -thr NET_C
Is there any other/better way anyone can think of?
Did anybody else face this kind of problem?
Does anybody else want a solution for this, from Synopsys?
- Srikant R Modugula
SGS-Thomson Microelectronics, New Delhi, India
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