Specman - BFM is created though it shouldn't - verification

Question

I have a BFM in my tx agent (without a sequence driver).
extend uart_tx_agent_u{
uart_tx_monitor : TX uart_monitor_u is instance;
uart_tx_scb: uart_tx_scoreboard_u is instance;
when ACTIVE uart_tx_agent_u {
uart_bfm : uart_tx_bfm_u is instance;
};
};
When I run the test (I don't change the active_passive field) I can see that the uart_bfm was created (according messages which are printed).

Answer 1

Are you sure you want to change the constraint from test to test? Either the agent is active and sends data to the DUT, or it is passive and only collects data sent from the DUT.
What people usually do is to define the agent as ACTIVE, so that it has a sequence driver and a BFM.
In the test files, you define the scenarios for the tests, by defining the sequences for this agent.
So in tests that you do not want to send any data to the DUT from this agent, set the sequence to do nothing -
extend MAIN my_seq {
body() #drive.clock is only {
// do nothing, this agent should not send data in this test
};
};
If you really want to change the environment topology, and in some tests the agent is to be PASSIVE and in some to be ACTIVE, you can do this in the test file, by constraining the agent.
And this constraint has to be in the pre-run generation.
Through the test - the agent is either ACTIVE or not. This cannot be change during the run. You cannot say "i start the test with a PASSIVE agent, but during the test i want to make it ACTIVE".

Answer 2

If the bfm is instantiated, it must be that the uart_tx_agent_u is ACTIVE.
when you say you don not change it - maybe it was randomly set to ACTIVE?

Answer 3

a sequence struct is being generated after the test starts. and a sequence is generated only if there is a driver. and a driver is instantiated only if the agent is ACTIVE.
environment topology should be constrained top down, not to constrain a unit from a struct that is contained in it
if you know you want to agent to be ACTIVE, then constrain it -
extend rx_uart_agent_u {
keep active_passive == TRUE;
};
or from its parent
extend env {
keep me.rx_agent.active_passive == TRUE;
};