Finding out which vmm callbacks are registered with a particular vmm_xactor instance

Avinash Agrawal, Corporate Applications, Synopsys

Is it possible to find out which VMM callbacks are registered with a particular vmm_xactor instance?

The answer is yes. Here’s how:

The vmm_xactor base class in VMM instantiates a queue of vmm_xactor_callbacks, callbacks[$]. So, it is possible to use the queue methods to find out details on the callbacks associated with an instance of the vmm_xactor class. To find out the number of callbacks associated with a vmm_xactor instance, we can use the size() function on the callbacks queue. And to list the names of the callbacks associated with the vmm_xactor instance, we can add a new string member (that would carry the name associated with the callback) to the classes derived from vmm_xactor_callbacks, and display this string variable as needed.

Here is an example. Assume that we have extended the vmm_xactor_callbacks class as follows. We also add a string name, that would carry the name associated
with the callback.

class atm_driver_callbacks extends vmm_xactor_callbacks ;
string name;
// Called before a transaction is executed
virtual task pre_trans_t(atm_driver master, atm_cell tr, ref bit drop); endtask
// Called after a transaction has been executed
virtual task post_trans_t(atm_driver master, atm_cell tr);endtask
endclass

The vmm_xactor instance can have a task as follows that displays the callbacks associated with that vmm_xactor instance, as the following example code shows:

task atm_driver::displaycallbacks;
begin
atm_driver_callbacks mycb = new();
$display(“2LOG : number of callbacks is %d\n”, callbacks.size());
$cast(mycb,callbacks[0]);
$display(“2LOG : callback[0] is %s\n”, mycb.name);
$cast(mycb,callbacks[1]);
$display(“2LOG : callback[1] %s\n”, mycb.name);
end
endtask

And, in the build() method of the environment, we have the following code:

//Instantiate the callback objects
atm_sb_callbacks atm_sb_cb = new();
atm_cov_callbacks atm_cov_cb = new();
atm_driver_callbacks mycb = new();
atm_cov_cb.name = “CBNAME1″;
atm_sb_cb.name =”CBNAME2″;

//Register the callbacks to the driver instance drv
this.drv.append_callback(atm_cov_cb);
this.drv.append_callback(atm_sb_cb);
//Call the xactor instance class method that displays the callbacks as follows:
this.drv.displaycallbacks;

This will produce the following output:
LOG : number of callbacks is 2
LOG : callback[0] is CBNAME1
LOG : callback[1] CBNAME2

As seen in the output pasted above, the names and the number of VMM callbacks are registered with the particular vmm_xactor instance, are displayed.