Production Rule Set

A production rule specifies either the pull-up or pull-down network of a gate in a QDI circuit. Many implicit inverters can be automatically added, feedback for stateholding or non-combinational gates is automatically generated, and sizing is automatically computed. For example a simple production rule set for a dataless buffer with a source for the input channel L and a sink for the output channel R would look like this.

require driven, stable, noninterfering
_Reset & R.e & L.r -> R.r+
R.r -> L.e-
~_Reset | ~R.e & ~L.r -> R.r-
~R.r -> L.e+

L.e -> L.r+
~L.e -> L.r-

R.r -> R.e-
~R.r -> R.e+

Production Rule

The syntax G -> S has a guard G and dataless assignment S. In states not covered by the guards, it is assumed that the assigned nodes remain at their previous states. This can be achieved using a keeper using either weak or combinational feedback. The most basic example is the C-element in which the guards do not cover the states where the two inputs are not the same value.

Require and Assume

At the top of the production rule file, you may specify a comma separated list of global behavioral constraints and assumptions. The following are supported:

assume nobackflow, static
require driven, stable, noninterfering, adiabatic

• assume nobackflow - NMOS transistors no longer drives a weak 1 and PMOS transistors no longer drive a weak 0.
• assume static - Undriven nodes keep their value instead of drifting to X. The strength still drifts to undriven.
• require driven - An error is thrown when a floating node is detected.
• require stable - An error is thrown when a glitch is detected.
• require noninterfering - An error is thrown when a short is detected.
• require adiabatic - An error is thrown when a transition on the gate of a transistor connects source to drain when they are not already the same voltage.

Pass Transistor Logic

The source node of guard may be specified using @source & G -> S. This allows you to efficiently write pass transistor logic or shared gate networks.

Anonymous Nodes

Anonymous nodes must follow the naming pattern _0 where 0 can be any integer number.

Flags

Behaviors for specific production rules can be tuned using various flags as follows G -> S [flag...]. The following flags are supported.

• keep - This net holds its value when it’s not driven. We’re assuming a keeper on this node.
• weak - The transistors in this production rule are weak and can be overridden by any other non-weak production rule. Use this for keepers.
• force - The transistors in this production rule are very strong and cannot be overridden at all. This also overrides normal production rules. Use this for power rails.
• pass - The production rule allows bi-directional current flow from source to drain or from drain to source.
• after=0 - Specify a maximum delay for this production rule where 0 can be any integer representing some number of pico-seconds.

Timing Assumptions

Timing assumptions may be optionally specified using the following syntax: G0 -> S {G1}. This will block the production rule from firing as long as G1 evaluates to GND. Instabilities on G1 do not propagate out into the rest of the circuit.

Examples

With weak feedback, shared gate networks, and anonymous nodes, and sizing, the above turns into this:

require driven, stable, noninterfering
@_3&R.r<1>|_Reset<3>&L.r<3>&R.e<3>->v1-
~v1<1>->R.r+
R.r<1>->L.e-
@_4&~R.r<1>|~_Reset<1>|~L.r<2>&~R.e<2>->v1+
v1<1>->R.r-
~R.r<1>->L.e+

L.e'1<1>->v0-
~v0<1>->L.r'1+
~L.e'1<1>->v0+
v0<1>->L.r'1-

R.r'1<1>->R.e'1-
~R.r'1<1>->R.e'1+

Vdd<0.1>->_3- [weak]
~GND<0.1>->_4+ [weak]