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  • Randomizing field depending on the previous transaction

Randomizing field depending on the previous transaction

SystemVerilog 4972
constraint randomization 29
AMARDEEP R PALURU
AMARDEEP R PALURU
Full Access
11 posts
August 05, 2016 at 7:14 am

In my sequence, I call

`uvm_create(item)
item.randomize with { trans_type inside {READ, WRITE}; };
`uvm_send(item)

I want to send a READ transaction immediately after a WRITE transaction every time. How do I achieve that ?

Replies

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dave_59
dave_59
Forum Moderator
8574 posts
August 05, 2016 at 7:35 am

What you need to do is randomize the same item repeatedly and send its clone. You can use a const cast to have the solver treat the expression as a constant value, the value it had before calling randomize().

`uvm_create(item)
repeat( some_number) begin
        item.randomize with { trans_type inside {READ, WRITE}; 
                              const'(trans_type) == WRITE -> trans_type == READ;};
       `uvm_send(item.clone())
      end

— Dave Rich, Verification Architect, Siemens EDA

Srini @ CVCblr.com
Srini @ CVCblr.com
Full Access
248 posts
August 05, 2016 at 7:49 am

In reply to AMARDEEP R PALURU:

Thinking loud about your problem statement - won't you need the address and other related fields also to be same as previous transaction? If yes I suggest you simply do:

// after first uvm_send
if (trans_type == WRITE)
begin
req.trans_type = READ;
uvm_send(req)

Regards
Srini

P.S. Lazy syntax as I am on mobile

AMARDEEP R PALURU
AMARDEEP R PALURU
Full Access
11 posts
August 05, 2016 at 8:00 am

In reply to dave_59:

Dave,
I didn't understand two things. Why are we randomizing it multiple times and why to clone before sending ?

dave_59
dave_59
Forum Moderator
8574 posts
August 05, 2016 at 8:09 am

In reply to AMARDEEP R PALURU:
You didn't explain your situation very well, and I was just assuming you are sending multiple random transactions in a some kind of a loop. You need to explain your sequence fully if that doesn't help you.

The reason you need to clone the transaction is because `uvm_send just passes a handle to the sequencer which it eventually passes to a driver. Both the sequencer and driver modify fields of your transaction and if you sent the same handle multiple times, they would overwrite each other.

— Dave Rich, Verification Architect, Siemens EDA

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