Examples of when to use Access APIs for UVM_REG

[lisakb1963]

Experts,

I understand basic Read and Write API (FRONTDOOR/BACKDOOR)

I understand why we need update() and mirror() -- for the SV Randomize.

Why would we want the get() and set() that just modifies the desired value. Under what circumstances is it desirable to use these?

[KathleenMeade]

Hello,

get() and set() are used to modify the register model directly instead of doing something like reg_model.block.reg.field=1. (which I don't think you can do anyway because they should be protected).

This might be used when your testbench can predict the value of a register field based on what is happening in the testbench. For example. An interrupt status register may be a read-only register. And if you want to read that register and do a real check of the value, you would have to identify that an interrupt occurred in your testbench – and then update that desired value directly. This is how you would do it. I guess it is used to update a register in the register model when it is modified by the DUT (instead of by generating stimulus).

I hope this helps!

Kathleen

[janick]

What Kathleen describes is the predict() method.

The set()/get() is used when you want to do batch updates. Instead of causing a write/read operation every time to need to set or read a register, you can set its desired value or get its mirrored value in zero-time, then batch-update the model only for those values that have changed.

So you have the choice of two use models: read-write-read-write or mirror-get-set-get-set-update

[lisakb1963]

Hi Janick,

How would I know I want to use batch updates? I am assuming based on comments --- that this is related to DUT changing registers. This would be part of the monitor activity of a variety of DUT changing registers (Counters, Interrupts, One register action reflecting another .... ). The documentation is a little skimpy on this in the UG (It only shows a hard-coded path). I always have to use a hard RTL path and I want to leverage the Register Model -- it does know the backdoor path. But I cannot pass it in to wait_for_change because it's a string , not an uvm_object. What I really want to know is the Accellera use model of dealing with DUT changing registers.

Reading back on your answer. I am asking a separate question here -- unrelated to the use model of get/set -- Sorry.