KEY Pin sides must match block communication; mismatched pin assignment causes routing problems.

Channel Spacing Between Macros

A common estimate for channel spacing is: (number of pins x routing pitch) divided by (total metal layers / 2).

KEY Channel spacing = (pins x pitch) / (metal layers / 2).

Macro Abutment

Two situations arise:

• If the two macros only talk to each other, abutment is acceptable.
• If they also connect to standard cells or IO ports, a proper channel must be left between them, otherwise routing congestion results.

KEY Abutment is fine only if the macros communicate solely with each other.

Macro Rotation Limits

It depends on the technology node. At 45nm and below the foundry imposes orientation rules - poly direction must stay consistent across the chip, so a macro's poly orientation has to match that of the standard cells.

KEY Allowed only if poly orientation stays consistent, advanced nodes restrict macro rotation.

Pad-Limited vs Core-Limited Designs

Pad-limited design: the die size is set by the pad area, and the IO pad count tends to be large. If die area is constrained, staggered IO pads can be used.

Core-limited design: the die size is set by the core area, and the IO pad count is generally smaller. In-line IOs can be used here.

KEY Pad-limited dies are bounded by pad area (staggered IOs); core-limited dies are bounded by core area (in-line IOs).