Inertial vs Transport
Delays

VHDL can model two types of delay in a component:

• Inertial delay - if two events occur on an input of the component with an interval time less that the defined delay, the output will not reflect either input event, and
• Transport delay - Any event on an input of the component will be reflected on the output.

The default timing type is inertial. If you want to model a transport delay, use the keyword "transport".

Transport delays are typically used to synchronize timing between VHDL processes and to model systems at high levels where inertial delay effects are ignored.