By default any logic/cell in the given by power domain will use the domain primary supply to power that logic. To override this default rule user can explicitly write connect_supply_net command to connect the any specific PG pin of the cell with needed supply net in UPF.
Let us understand this with example.
Why this is needed . Consider a level shifter cell , which has 2 power net. Now connecting both the power net to a domain primary power net will end up in electrical problem. So one PG pin can be connected to domain primary power net which will be by default. For another PG pin we can use connect_supply_net command to connect it to a required supply net in UPF.
Design :
module top (in1,..);
LS_CELL i_ls (.A(in1),.Z(w1));
endmodule
UPF:
create_supply_net VDD
connect_supply_net VDD -ports {i_ls/VDD1}
Let us understand this with example.
Why this is needed . Consider a level shifter cell , which has 2 power net. Now connecting both the power net to a domain primary power net will end up in electrical problem. So one PG pin can be connected to domain primary power net which will be by default. For another PG pin we can use connect_supply_net command to connect it to a required supply net in UPF.
Design :
module top (in1,..);
LS_CELL i_ls (.A(in1),.Z(w1));
endmodule
UPF:
create_supply_net VDD
connect_supply_net VDD -ports {i_ls/VDD1}
module top (in1,Z,VDD);
ReplyDeleteLS_CELL i_ls (.A(in1),.Z(w1),.VDD());
endmodule
In this condition if I have not connected LS VDD supply with TOP VDD supply than by default LS cell will take TOP VDD supply or the supply will be zero for LS cell ?
It will get connected to TOP VDD if there no explicit CSN to LS VDD. If CSN is there than it will honor CSN supply.
DeleteWhen I follow the above method, I'm getting a warning saying the inout port i_ls/VDD1, is taken as input port
ReplyDeleteNow since the port VDD1 is input and not output to that scope or block, the VDD1 value is always x since the upf is expecting us to drive it and the i_ls is also expect the upf to drive VDD1
So myquestion is, is there anyway to specify a port as output?
Sorry but your question is not clear . May be can you please paste relevant part of design and upf. With this I might help you.
Delete