uvm_transaction

The uvm_transaction class is the root base class for UVM transactions.  Inheriting all the methods of uvm_object, uvm_transaction adds a timing and recording interface.

This class provides timestamp properties, notification events, and transaction recording support.

Use of this class as a base for user-defined transactions is deprecated.  Its subtype, uvm_sequence_item, shall be used as the base class for all user-defined transaction types.

The intended use of this API is via a uvm_driver #(REQ,RSP) to call uvm_component::accept_tr, uvm_component::begin_tr, and uvm_component::end_tr during the course of sequence item execution.  These methods in the component base class will call into the corresponding methods in this class to set the corresponding timestamps (accept_time, begin_time, and end_time), trigger the corresponding event (begin_event and end_event, and, if enabled, record the transaction contents to a vendor-specific transaction database.

Note that get_next_item/item_done when called on a uvm_seq_item_pull_port will automatically trigger the begin_event and end_events via calls to begin_tr and end_tr.  While convenient, it is generally the responsibility of drivers to mark a transaction’s progress during execution.  To allow the driver or layering sequence to control sequence item timestamps, events, and recording, you must call uvm_sqr_if_base#(REQ,RSP)::disable_auto_item_recording at the beginning of the driver’s run_phase task.

Users may also use the transaction’s event pool, events, to define custom events for the driver to trigger and the sequences to wait on.  Any in-between events such as marking the beginning of the address and data phases of transaction execution could be implemented via the events pool.

In pipelined protocols, the driver may release a sequence (return from finish_item() or it’s `uvm_do macro) before the item has been completed.  If the driver uses the begin_tr/end_tr API in uvm_component, the sequence can wait on the item’s end_event to block until the item was fully executed, as in the following example.

task uvm_execute(item, ...);
    // can use the `uvm_do macros as well
    start_item(item);
    item.randomize();
    finish_item(item);
    item.end_event.wait_on();
    // get_response(rsp, item.get_transaction_id()); //if needed
endtask

A simple two-stage pipeline driver that can execute address and data phases concurrently might be implemented as follows:

task run();
    // this driver supports a two-deep pipeline
    fork
      do_item();
      do_item();
    join
endtask


task do_item();

  forever begin
    mbus_item req;

    lock.get();

    seq_item_port.get(req); // Completes the sequencer-driver handshake

    accept_tr(req);

      // request bus, wait for grant, etc.

    begin_tr(req);

      // execute address phase

    // allows next transaction to begin address phase
    lock.put();

      // execute data phase
      // (may trigger custom "data_phase" event here)

    end_tr(req);

  end

endtask: do_item
Summary
uvm_transaction
The uvm_transaction class is the root base class for UVM transactions.
Class Hierarchy
uvm_void
uvm_object
uvm_transaction
Class Declaration
virtual class uvm_transaction extends uvm_object
Methods
newCreates a new transaction object.
accept_trCalling accept_tr indicates that the transaction item has been received by a consumer component.
do_accept_trThis user-definable callback is called by accept_tr just before the accept event is triggered.
begin_trThis function indicates that the transaction has been started and is not the child of another transaction.
begin_child_trThis function indicates that the transaction has been started as a child of a parent transaction given by parent_handle.
do_begin_trThis user-definable callback is called by begin_tr and begin_child_tr just before the begin event is triggered.
end_trThis function indicates that the transaction execution has ended.
do_end_trThis user-definable callback is called by end_tr just before the end event is triggered.
get_tr_handleReturns the handle associated with the transaction, as set by a previous call to begin_child_tr or begin_tr with transaction recording enabled.
disable_recordingTurns off recording for the transaction stream.
enable_recordingTurns on recording to the stream specified.
is_recording_enabledReturns 1 if recording is currently on, 0 otherwise.
is_activeReturns 1 if the transaction has been started but has not yet been ended.
get_event_poolReturns the event pool associated with this transaction.
set_initiatorSets initiator as the initiator of this transaction.
get_initiatorReturns the component that produced or started the transaction, as set by a previous call to set_initiator.
get_accept_time
get_begin_time
get_end_timeReturns the time at which this transaction was accepted, begun, or ended, as by a previous call to accept_tr, begin_tr, begin_child_tr, or end_tr.
set_transaction_idSets this transaction’s numeric identifier to id.
get_transaction_idReturns this transaction’s numeric identifier, which is -1 if not set explicitly by set_transaction_id.
Variables
eventsThe event pool instance for this transaction.
begin_eventA uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus begins, typically as a result of a driver calling uvm_component::begin_tr.
end_eventA uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus ends, typically as a result of a driver calling uvm_component::end_tr.

Methods

new

function new (
    string  name  =  "",
    uvm_component  initiator  =  null
)

Creates a new transaction object.  The name is the instance name of the transaction.  If not supplied, then the object is unnamed.

accept_tr

function void accept_tr (
    time  accept_time  =  0
)

Calling accept_tr indicates that the transaction item has been received by a consumer component.  Typically a uvm_driver #(REQ,RSP) would call uvm_component::accept_tr, which calls this method-- upon return from a get_next_item(), get(), or peek() call on its sequencer port, uvm_driver#(REQ,RSP)::seq_item_port.

With some protocols, the received item may not be started immediately after it is accepted.  For example, a bus driver, having accepted a request transaction, may still have to wait for a bus grant before beginning to execute the request.

This function performs the following actions

  • The transaction’s internal accept time is set to the current simulation time, or to accept_time if provided and non-zero.  The accept_time may be any time, past or future.
  • The transaction’s internal accept event is triggered.  Any processes waiting on the this event will resume in the next delta cycle.
  • The do_accept_tr method is called to allow for any post-accept action in derived classes.

do_accept_tr

virtual protected function void do_accept_tr ()

This user-definable callback is called by accept_tr just before the accept event is triggered.  Implementations should call super.do_accept_tr to ensure correct operation.

begin_tr

function integer begin_tr (
    time  begin_time  =  0
)

This function indicates that the transaction has been started and is not the child of another transaction.  Generally, a consumer component begins execution of a transactions it receives.

Typically a uvm_driver #(REQ,RSP) would call uvm_component::begin_tr, which calls this method, before actual execution of a sequence item transaction.  Sequence items received by a driver are always a child of a parent sequence.  In this case, begin_tr obtains the parent handle and delegates to begin_child_tr.

See accept_tr for more information on how the begin-time might differ from when the transaction item was received.

This function performs the following actions

  • The transaction’s internal start time is set to the current simulation time, or to begin_time if provided and non-zero.  The begin_time may be any time, past or future, but should not be less than the accept time.
  • If recording is enabled, then a new database-transaction is started with the same begin time as above.
  • The do_begin_tr method is called to allow for any post-begin action in derived classes.
  • The transaction’s internal begin event is triggered.  Any processes waiting on this event will resume in the next delta cycle.

The return value is a transaction handle, which is valid (non-zero) only if recording is enabled.  The meaning of the handle is implementation specific.

begin_child_tr

function integer begin_child_tr (
    time  begin_time  =  0,
    integer  parent_handle  =  0
)

This function indicates that the transaction has been started as a child of a parent transaction given by parent_handle.  Generally, a consumer component calls this method via uvm_component::begin_child_tr to indicate the actual start of execution of this transaction.

The parent handle is obtained by a previous call to begin_tr or begin_child_tr.  If the parent_handle is invalid (=0), then this function behaves the same as begin_tr.

This function performs the following actions

  • The transaction’s internal start time is set to the current simulation time, or to begin_time if provided and non-zero.  The begin_time may be any time, past or future, but should not be less than the accept time.
  • If recording is enabled, then a new database-transaction is started with the same begin time as above.  The inherited uvm_object::record method is then called, which records the current property values to this new transaction.  Finally, the newly started transaction is linked to the parent transaction given by parent_handle.
  • The do_begin_tr method is called to allow for any post-begin action in derived classes.
  • The transaction’s internal begin event is triggered.  Any processes waiting on this event will resume in the next delta cycle.

The return value is a transaction handle, which is valid (non-zero) only if recording is enabled.  The meaning of the handle is implementation specific.

do_begin_tr

virtual protected function void do_begin_tr ()

This user-definable callback is called by begin_tr and begin_child_tr just before the begin event is triggered.  Implementations should call super.do_begin_tr to ensure correct operation.

end_tr

function void end_tr (
    time  end_time  =  0,
    bit  free_handle  =  1
)

This function indicates that the transaction execution has ended.  Generally, a consumer component ends execution of the transactions it receives.

You must have previously called begin_tr or begin_child_tr for this call to be successful.

Typically a uvm_driver #(REQ,RSP) would call uvm_component::end_tr, which calls this method, upon completion of a sequence item transaction.  Sequence items received by a driver are always a child of a parent sequence.  In this case, begin_tr obtain the parent handle and delegate to begin_child_tr.

This function performs the following actions

  • The transaction’s internal end time is set to the current simulation time, or to end_time if provided and non-zero.  The end_time may be any time, past or future, but should not be less than the begin time.
  • If recording is enabled and a database-transaction is currently active, then the record method inherited from uvm_object is called, which records the final property values.  The transaction is then ended.  If free_handle is set, the transaction is released and can no longer be linked to (if supported by the implementation).
  • The do_end_tr method is called to allow for any post-end action in derived classes.
  • The transaction’s internal end event is triggered.  Any processes waiting on this event will resume in the next delta cycle.

do_end_tr

virtual protected function void do_end_tr ()

This user-definable callback is called by end_tr just before the end event is triggered.  Implementations should call super.do_end_tr to ensure correct operation.

get_tr_handle

function integer get_tr_handle ()

Returns the handle associated with the transaction, as set by a previous call to begin_child_tr or begin_tr with transaction recording enabled.

disable_recording

function void disable_recording ()

Turns off recording for the transaction stream.  This method does not effect a uvm_component’s recording streams.

enable_recording

function void enable_recording (
    uvm_tr_stream  stream
)

Turns on recording to the stream specified.

If transaction recording is on, then a call to record is made when the transaction is ended.

is_recording_enabled

function bit is_recording_enabled()

Returns 1 if recording is currently on, 0 otherwise.

is_active

function bit is_active ()

Returns 1 if the transaction has been started but has not yet been ended.  Returns 0 if the transaction has not been started.

get_event_pool

function uvm_event_pool get_event_pool ()

Returns the event pool associated with this transaction.

By default, the event pool contains the events: begin, accept, and end.  Events can also be added by derivative objects.  An event pool is a specialization of uvm_pool#(KEY,T), e.g. a uvm_pool#(uvm_event).

set_initiator

function void set_initiator (
    uvm_component  initiator
)

Sets initiator as the initiator of this transaction.

The initiator can be the component that produces the transaction.  It can also be the component that started the transaction.  This or any other usage is up to the transaction designer.

get_initiator

function uvm_component get_initiator ()

Returns the component that produced or started the transaction, as set by a previous call to set_initiator.

get_accept_time

function time get_accept_time ()

get_begin_time

function time get_begin_time ()

get_end_time

function time get_end_time ()

Returns the time at which this transaction was accepted, begun, or ended, as by a previous call to accept_tr, begin_tr, begin_child_tr, or end_tr.

set_transaction_id

function void set_transaction_id(
    integer  id
)

Sets this transaction’s numeric identifier to id.  If not set via this method, the transaction ID defaults to -1.

When using sequences to generate stimulus, the transaction ID is used along with the sequence ID to route responses in sequencers and to correlate responses to requests.

get_transaction_id

function integer get_transaction_id()

Returns this transaction’s numeric identifier, which is -1 if not set explicitly by set_transaction_id.

When using a uvm_sequence #(REQ,RSP) to generate stimulus, the transaction ID is used along with the sequence ID to route responses in sequencers and to correlate responses to requests.

Variables

events

const uvm_event_pool events = new

The event pool instance for this transaction.  This pool is used to track various milestones: by default, begin, accept, and end

begin_event

uvm_event#(
    uvm_object
) begin_event

A uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus begins, typically as a result of a driver calling uvm_component::begin_tr.  Processes that wait on this event will block until the transaction has begun.

For more information, see the general discussion for uvm_transaction.  See uvm_event#(T) for details on the event API.

end_event

uvm_event#(
    uvm_object
) end_event

A uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus ends, typically as a result of a driver calling uvm_component::end_tr.  Processes that wait on this event will block until the transaction has ended.

For more information, see the general discussion for uvm_transaction.  See uvm_event#(T) for details on the event API.

virtual task my_sequence::body();
 ...
 start_item(item);    \
 item.randomize();     } `uvm_do(item)
 finish_item(item);   /
 // return from finish item does not always mean item is completed
 item.end_event.wait_on();
 ...
virtual class uvm_void
The uvm_void class is the base class for all UVM classes.
virtual class uvm_object extends uvm_void
The uvm_object class is the base class for all UVM data and hierarchical classes.
virtual class uvm_transaction extends uvm_object
The uvm_transaction class is the root base class for UVM transactions.
function new (
    string  name  =  "",
    uvm_component  initiator  =  null
)
Creates a new transaction object.
function void accept_tr (
    time  accept_time  =  0
)
Calling accept_tr indicates that the transaction item has been received by a consumer component.
virtual protected function void do_accept_tr ()
This user-definable callback is called by accept_tr just before the accept event is triggered.
function integer begin_tr (
    time  begin_time  =  0
)
This function indicates that the transaction has been started and is not the child of another transaction.
function integer begin_child_tr (
    time  begin_time  =  0,
    integer  parent_handle  =  0
)
This function indicates that the transaction has been started as a child of a parent transaction given by parent_handle.
virtual protected function void do_begin_tr ()
This user-definable callback is called by begin_tr and begin_child_tr just before the begin event is triggered.
function void end_tr (
    time  end_time  =  0,
    bit  free_handle  =  1
)
This function indicates that the transaction execution has ended.
virtual protected function void do_end_tr ()
This user-definable callback is called by end_tr just before the end event is triggered.
function integer get_tr_handle ()
Returns the handle associated with the transaction, as set by a previous call to begin_child_tr or begin_tr with transaction recording enabled.
function void disable_recording ()
Turns off recording for the transaction stream.
function void enable_recording (
    uvm_tr_stream  stream
)
Turns on recording to the stream specified.
function bit is_recording_enabled()
Returns 1 if recording is currently on, 0 otherwise.
function bit is_active ()
Returns 1 if the transaction has been started but has not yet been ended.
function uvm_event_pool get_event_pool ()
Returns the event pool associated with this transaction.
function void set_initiator (
    uvm_component  initiator
)
Sets initiator as the initiator of this transaction.
function uvm_component get_initiator ()
Returns the component that produced or started the transaction, as set by a previous call to set_initiator.
function time get_accept_time ()
function time get_begin_time ()
function time get_end_time ()
Returns the time at which this transaction was accepted, begun, or ended, as by a previous call to accept_tr, begin_tr, begin_child_tr, or end_tr.
function void set_transaction_id(
    integer  id
)
Sets this transaction’s numeric identifier to id.
function integer get_transaction_id()
Returns this transaction’s numeric identifier, which is -1 if not set explicitly by set_transaction_id.
const uvm_event_pool events = new
The event pool instance for this transaction.
uvm_event#(
    uvm_object
) begin_event
A uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus begins, typically as a result of a driver calling uvm_component::begin_tr.
function integer begin_tr (
    uvm_transaction  tr,   
    string  stream_name  =  "main",
    string  label  =  "",
    string  desc  =  "",
    time  begin_time  =  0,
    integer  parent_handle  =  0
)
This function marks the start of a transaction, tr, by this component.
uvm_event#(
    uvm_object
) end_event
A uvm_event#(uvm_object) that is triggered when this transaction’s actual execution on the bus ends, typically as a result of a driver calling uvm_component::end_tr.
function void end_tr (
    uvm_transaction  tr,   
    time  end_time  =  0,
    bit  free_handle  =  1
)
This function marks the end of a transaction, tr, by this component.
class uvm_sequence_item extends uvm_transaction
The base class for user-defined sequence items and also the base class for the uvm_sequence class.
class uvm_driver #(
    type  REQ  =  uvm_sequence_item,
    type  RSP  =  REQ
) extends uvm_component
The base class for drivers that initiate requests for new transactions via a uvm_seq_item_pull_port.
function void accept_tr (
    uvm_transaction  tr,   
    time  accept_time  =  0
)
This function marks the acceptance of a transaction, tr, by this component.
virtual function void disable_auto_item_recording()
By default, item recording is performed automatically when get_next_item() and item_done() are called.
Derived driver classes should use this port to request items from the sequencer.
function integer begin_child_tr (
    uvm_transaction  tr,   
    integer  parent_handle  =  0,
    string  stream_name  =  "main",
    string  label  =  "",
    string  desc  =  "",
    time  begin_time  =  0
)
This function marks the start of a child transaction, tr, by this component.
function void record (
    uvm_recorder  recorder  =  null
)
The record method deep-records this object’s properties according to an optional recorder policy.
virtual class uvm_component extends uvm_report_object
The uvm_component class is the root base class for UVM components.
class uvm_pool #(
    type  KEY  =  int,
      T  =  uvm_void
) extends uvm_object
Implements a class-based dynamic associative array.
virtual class uvm_sequence #(
    type  REQ  =  uvm_sequence_item,
    type  RSP  =  REQ
) extends uvm_sequence_base
The uvm_sequence class provides the interfaces necessary in order to create streams of sequence items and/or other sequences.
class uvm_event#(
    type  T  =  uvm_object
) extends uvm_event_base
The uvm_event class is an extension of the abstract uvm_event_base class.