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How TLM Works

Contents are extracted from the Advanced UVM sessions by Verification Academy.

TLM​

TLM is all about communication through method calls

  • A TLM port specifies the “API” to be used
  • A TLM export supplies the implementation of the methods

Connections are between ports/exports, not components

Transaction are objects

Ports & exports are parameterized with the type of the transaction being communicated

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Factory can be used to change the component’s type, as long as it is similar type and have the same set of interfaces

Hierarchical connections​

Port-to-Export​

port.connect(export);

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Port-to-Port​

child.port.connect(parent_port);

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Export-to-Export​

parent_export.connect(child.export);

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Last export is actually an ‘imp’​

The source use the interface

The target supply the implementation of the interface

The implementation contains the transaction type and type of the component contains the implementation

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The transaction flow from C1 → C2 and C2 will do something with it

⇒ Factory override is also possible, C2X having different implementation on the put task

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Analysis Communication​

Analysis ports support 1:n connections

  • All write() functions called in zero time

Used by coverage collectors and scoreboards

  • uvm_subscriber has built-in analysis_export

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Every components connect to the analysis_port will have an implementation of the write() method

When one subscriber made one change on the transaction, all other subscribers will know the changes

Recommended to make a copy of the transaction handle when implementing the write() method

Analysis of multiple streams​

The uvm_subscriber only support single connection to analysis_port

Choice 1: Use imp suffixes defined via macro

  • Declare macros outside of component
  • Instantiate suffixed imps
  • Implement write_SUFFIX methods

Write methods are functions

  • Can’t synchronize between streams

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Choice 2: Use embedded FIFOs (recommended)

  • Declare analysis exports
  • Connect exports to FIFOs

run_phase can now actively pull from FIFOs

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TLM2 in UVM​

TLM2: SystemC’s feature

TLM2 based on a generic_payload transaction base class

  • TLM2 uses sockets, which contain both a port and an export
  • Pass-by-reference (pass-by-value in TLM1)
  • The generic payload can be extended to model any kind of transaction

Connections are between sockets, just like ports/exports

  • Initiator socket connects to target socket

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Blocking transport​

Completes the entire transaction within a single method call

  • Uses the b_transport() task

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Nonblocking transport​

Bidirectional communication

  • Uses the nb_transport_fw() and nb_transport_bw() functions
  • Initiator implements the nb_transport_bw()
  • Target implements the nb_transport_fw()

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uvm_tlm_sync_e: Indicates the status of the transaction

Pass through sockets

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Generic Payload​

All elements are rand and protected

Must use predefined virtual accessor methods

Defined to be either READ, WRITE or IGNORE command

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Summary​

Every port must eventually connect to an implementation (imp)

Mostly only use 2 port/export connections:

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All TLM connections go from ‘origin’ to ‘destination’

  • port.connect(export);
  • child_port.connect(parent_port);
  • parent_export.connect(child_export);