2LM sclib Standard Cell Library

This paper describes how to use the current version of the Alliance software with the sclib. The sclib is a 2-layer metal standard cell library designed by the Alliance software authors. It was released with the Alliance software until version 4.0 and can be downloaded as part of the software release at http://www-asim.lip6.fr/pub/alliance/distribution/4.0.

The characterisation has been done for a 0.5µm technology. The library contains 50 cells in the same basic views as the more recent sxlib. It appears to have been designed in 1998 for a 2-layer metal process. This kind of library uses metal-2 to bring the cell connections to the top and bottom of each cell. Each cell row is separated by a routing channel with horizontal metal-1 and vertical metal-2.

Typically 2-layer metal standard cell libraries were designed without any internal metal-2 where possible, so that the free tracks could be used for global routing. The sclib follows this approach, with only the flip-flops using internal metal-2.

The current P&R software, OCP and NERO cannot place and route 2-layer metal libraries using metal-1 and metal-2. The standard cell place software OCP places the cell rows in alternate flip and abut so that the interconnect runs over the top of the cells, and cannot open up free channel for routing. The router NERO won't route metal-1 at all.

However, the Alliance software is flexible and the sclib can be used with the current software after some modifications have been made

• to the library itself
• to the program source code and
• to the support files.

Scripts are used to link various phases of the design flow.

All of this is described in the following chapters. Apart from showing how to place and route a 2-layer standard cell design, the paper shows how the Alliance software can be adapted to handle situations which are significantly different to the original Alliance sxlib for which it was designed.