Specman e: How driver's items queue can be locked from a sequence?

Question

In my verification environment, there are few sequences running simultaneously on the same driver (there is no matter when an item gets the bus in relation to other sequences' items).

BUT, now I need to add additional sequence, that will run simultaneously to other sequences, that executes atomic read-modify-write. My new sequence looks something like this:

// Atomic READ-MODIFY-WRITE
body() @driver.clock is only {

    do read_item keeping {
        .cmd                == RD; 
        .addr               == addr;
    };

    // Wait random time;

    do write_item keeping {
        .cmd                == WR;
        .addr               == addr;
        .data               == data;  
    };
};

The problem is that between the read_item and write_item, items from other sequences get the bus. Do you have any idea how the driver's item queue can be locked from a sequence? So I can prevent other sequences to add their items in between my read and write items?

Thank you for your help

Answer 1

You can use the grab(...) and ungrab(...) methods of any_sequence to get exclusive access to the sequence driver:

// Atomic READ-MODIFY-WRITE
body() @driver.clock is only {

    grab(driver);

    do read_item keeping {
        .cmd                == RD; 
        .addr               == addr;
    };

    // Wait random time;

    do write_item keeping {
        .cmd                == WR;
        .addr               == addr;
        .data               == data;  
    };

    ungrab(driver);
};

While the driver is grabbed, no other sequence can send items to the it.