TMR Strategies

TMRX supports two complementary TMR strategies that can be mixed within the same design hierarchy.

Logic TMR

Logic TMR triplicates the internal logic of a module while optionally preserving the original interface.

What Gets Triplicated

All combinational logic gates
All wires and signals
All flip-flops
All internal connections

How It Works

Every wire and cell is duplicated with configurable suffixes (for example, _a, _b, _c).
Majority voters are inserted after flip-flop outputs (configurable).
If preserve_module_ports = true, voters are inserted at outputs to maintain the original interface.
If preserve_module_ports = false, the module interface is expanded with triplicated ports.

Full Module TMR

Full Module TMR creates a wrapper module containing three independent instances of the original module.

What Gets Created

A new wrapper module with the original module name
The original module renamed with a _tmrx_worker suffix
Three instances of the worker module inside the wrapper
Optional input voters (before modules)
Optional output voters (after modules)

How It Works

The original module is renamed and wrapped.
Three instances are created with connections to wrapper ports.
If preserve_module_ports = false, ports are triplicated.
Voters can be inserted at inputs, outputs, or both.

Choosing a Strategy

Consideration Logic TMR Full Module TMR

Consideration	Logic TMR	Full Module TMR
Interface changes	Optional (with `preserve_module_ports`)	Optional (with `preserve_module_ports`)
Voter placement	After FFs, at outputs	At module boundaries
Area overhead	Generally lower	Slightly higher (wrapper overhead)
Black-box modules	Not applicable	Required

Interface changes

Optional (with preserve_module_ports)

Voter placement

After FFs, at outputs

At module boundaries

Area overhead

Generally lower

Slightly higher (wrapper overhead)

Black-box modules

Not applicable

Required

Black-box modules (modules with the blackbox attribute, memories, or processes) are automatically assigned Full Module TMR because their internals cannot be modified.

Child Module Version Selection

When a design mixes TMR strategies, a parent module may instantiate a child that has been processed by TMRX. Which version of the child a parent sees depends on the child’s preserve_module_ports setting.

Child with preserve_module_ports = false

When a child module is expanded with preserve_module_ports = false, TMRX keeps two versions of it in the design:

The original module with its unchanged interface.
A _tmrx_impl clone with triplicated ports and TMR’d internals.

Which version a parent uses depends on the parent’s TMR mode:

Parent TMR mode Child version used

Parent TMR mode	Child version used
`LogicTMR`	`_tmrx_impl` — the TMR’d clone with triplicated ports. TMRX automatically remaps cell references during Logic TMR expansion.
`FullModuleTMR`	Original — the non-expanded module with its original interface. Each of the three worker copies instantiates the original child.
`None`	Original — the non-expanded module with its original interface. The parent is not processed by TMRX, so no remapping occurs.

LogicTMR

_tmrx_impl — the TMR’d clone with triplicated ports. TMRX automatically remaps cell references during Logic TMR expansion.

FullModuleTMR

Original — the non-expanded module with its original interface. Each of the three worker copies instantiates the original child.

None

Original — the non-expanded module with its original interface. The parent is not processed by TMRX, so no remapping occurs.

This means a child module that is TMR’d with preserve_module_ports = false is not redundant inside a FullModuleTMR or None parent. The three FullModuleTMR workers each hold one copy of the original child, and a None parent holds one copy as well.

Child with preserve_module_ports = true

When a child module is expanded with preserve_module_ports = true, there is only one version of the module. TMRX expands it in-place: the interface is unchanged, but the internals are now triplicated.

All parent modes — LogicTMR, FullModuleTMR, and None — instantiate this single module. Every parent therefore gets the TMR’d internals regardless of its own TMR mode.

Summary

Child preserve_module_ports Parent mode Child internals TMR’d?

Child `preserve_module_ports`	Parent mode	Child internals TMR’d?
`false`	`LogicTMR`	Yes — `_tmrx_impl` clone used
`false`	`FullModuleTMR`	No — original module used
`false`	`None`	No — original module used
`true`	Any	Yes — single in-place expanded module used

false

LogicTMR

Yes — _tmrx_impl clone used

false

FullModuleTMR

No — original module used

false

None

No — original module used

true

Any

Yes — single in-place expanded module used

If you want a TMR’d child module to be redundant inside a FullModuleTMR or None parent, set preserve_module_ports = true on the child. Without it, the child’s TMR expansion is invisible to those parent modes.