Magic Blue Smoke

 

Interpretation of UPF during Power Planning

So far we have seen how UPF gets interpreted during synthesis and verification . Today lets look at how UPF gets interpreted during Floorplanning/Power Planning ? This is the most important phase in the design cycle, where power grid required for the design gets implemented physically to get the required functionality.

Main concerns here are

(a) If part of my design is going to be shut-down, how do I insert special cells in the power grid to cut-off power?

(b) How do I validate, whether my grid is beefed up enough to provide required amount of current to the circuit?

(c) How Many special cells are required to efficiently build the power grid ?

(d) How long will it take for the circuit to wake-up after recieving the wake-up signal ?

(e) Should I worry about the wake-up or shut-down sequence of switches as well as standard cells connected to the switches ?

(f) Which Part of the UPF conveys all these information?

First lets look at the UPF, which will be used by Floorplanning/Power Planning tools to implement the grid.

create_power_switch rx_sw
-domain RECIEVER
-input_supply_port {in VDD_LOW}
-output_supply_port {out VDD_LOW_RX_VIRTUAL}
-control_port {rx_sd power_controller/rx_sd}
-on_state {rx_on_state in {!rx_sd}}

The above command says, we need to insert a switch in the domain reciever, whose input supply port is VDD_LOW and output of the switch is VDD_LOW_RX_VIRTUAL. All the components inside the domain reciever are going to be powered through the supply net “VDD_LOW_RX_VIRTUAL”. Now how do we know which switch cell to use?

this is specified through the UPF command

map_power_switch -domain RECIEVER -lib_cell

rx_sw

In my next post, lets see how these get implemented physically and what part of the power plan can be automated.