problem about synopsys synthesis

Rachel · Oct 25, 2003

I write verilog code as below :
always @(posedge clock or posedge rst)
if (rst)
reg1 <= 1'b0 ;
else
reg1 <= 1'b1 ;

Synopsys will synthesis this register with its input connected to VCC , I change some setting in .synopsys_setup ,and let it put a cell between system VCC with its input. The problem is I wish every register's input ( described like before) don't be connected to VCC directly and synopsys can put a cell between it and VCC. I hope one cell to one register , but synopsys will connect all the inputs and only put one cell between them and VCC . The cell is from a library provided by fab , I can't change its fanout . Can I disovle it by setting synthesis constraint ? Can anyone help me ?

cdic · Oct 25, 2003

synthesis it first, then wrote a script to change it. either in DC or directly modify the netlist. piece of a cake.

Rachel · Oct 26, 2003

cdic said:
synthesis it first, then wrote a script to change it. either in DC or directly modify the netlist. piece of a cake.

Do you mean I can change the schematic result by DC command ? Can you give me an example ? Thanks a lot!

cdic · Oct 28, 2003

Cells Create a cell create_cell
Delete a cell remove_cell
Nets Create a net create_net
Connect a net connect_net
Disconnect a net disconnect_net
Delete a net remove_net
Ports Create a port create_port
Delete a port remove_port
Buses Create a bus create_bus
Delete a bus remove_bus

rakko · Oct 29, 2003

Rachel,
how about attach your cell to vcc / ground and assign the other end of this cell to your register inside your always block.

example:

cell (.Z(wire1), .A(VCC));

always .....
if (rst)
reg1 <= 1'b0;
else
reg1 <= wire1;

rakko · Oct 29, 2003

deleted

maniasonic · Jan 8, 2004

you must don't have a cell that always out put a logic "1" in your cell library.

honey · Jan 14, 2004

inside your always block.

example:

cell (.Z(wire1), .A(VCC));

always .....
if (rst)
reg1 <= 1'b0;
else
reg1 <= wire1;

problem about synopsys synthesis

Rachel

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cdic

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Rachel

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cdic

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rakko

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