Sucking up the time

Conventional flows perform a single pass of a physical design, generating a floorplan and corresponding physical implementation. Changes to the design – including late engineering change orders (ECOs) – take place all the way up to tapeout, so it is often necessary to respin large portions of the physical implementation. This takes weeks and it is not uncommon to respin the entire design, including creating a new floorplan. With this flow, physical design engineers don’t engage in the process until the RTL is 90% complete; if they engage earlier, anything they do will almost certainly end up being scrapped. Once they engage, it typically takes six weeks to generate the initial floorplan and corresponding physical implementation. By the time the RTL is 95% complete, much of the original physical implementation will have been modified and upgraded; it typically takes another four weeks for the floorplan to be frozen. Even after the RTL is complete, it usually takes at least nine weeks before the final physical implementation is ready for tapeout. An alternative approach is to take the design RTL and perform the key tasks in parallel with the RTL coding. This enables quick feedback to the RTL designer.