Register backdoor write getting overwritten at next clock edge

[johnrossserco]

Backdoor write value deposited on the register variable appears to get overwritten on the next clock edge. See code below. If I move the write conditional into the always_ff block the backdoor access sticks. Where in the time slot does the backdoor DPI call get executed: prepone, observe, re-nba or postpone?

always_ff @(posedge clk) begin

reg_name <= reg_name_next;

end

always_comb begin

reg_name_next = reg_name;

if (write)

reg_name_next = write_data;

end

[janick]

The DPI gets called by the thread that calls the write() method and thus executes in the same region. And since it is a simple immediate variable assignment, it will get overwritten should/when other threads assign a different value.

What you have here is a classic race condition...

[johnrossserco]

Thanks for the reply. Is this a matter of UVM not supporting this coding style, or do I have to get smarter about when the write() method gets executed?