Register-Based Testing

Contents are extracted from the Advanced UVM sessions by Verification Academy.

Register-based analysis components

The register model mirror value is used by analysis components

• Scoreboards to check current DUT configuration
  • Where this may affect the checking algorithm
• Functional coverage monitors
  • What is the configuration at a triggered sample?

Analysis components access physical registers passively (using the backdoor accesses):

• No ability to drive the bus
• Backdoor read() or peek() accesses

They look up the register model values directly

• spi_rm.ctrl.get_mirrored_value(data);
• spi_rm.ctrl.value or spi_rm.ctrl.get(data);

Register Scoreboard guidelines

Scoreboard needs a handle to the register model

Scoreboard accesses register values from model

Scoreboard checks DUT register contents

• Compare observed data vs. register model contents
• Compare DUT contents vs. expected
  • via peek access to the DUT

Scoreboard checking

Functional coverage monitors

The register model has built-in functional coverage

A custom functional coverage monitor can be defined to sample based on significant events

• Interrupts
• Writes to certain trigger registers

Register Assistant generates ‘intelligent’ register access covergroup

• Included in the register package code

Functional coverage monitor example

Coding guideline

Always wrap a `covergroup` in a `uvm_object` wrapper

Allow the ability to override covergroup when necessary (uvm_object is overridden)

Monitor with Wrapped covergroup

Modeling memory

The register model provides access to memory region

• mem.read()/mem.write() to location x in memory y

• The memory location address offset is calculated

  mem.read(status, offset_addr, data, ...);
  mem.write(status, offset_addr, data, ...);

The model does not shadow memory regions

• DUT memories are usually modelled separately
• Maintaining a memory shadow is expensive
• No set() / get() functions available

Memory accesses can support bursts

• mem.burst_read()
• mem.burst_write()

Example memory based sequence

Built-in Memory sequences

Register Summary

Register block contains

• Register model
  • Fields
• Address Map
• Sub-blocks

Register analysis components have register block pointer

• Access via get() or backdoor read/peek
• Use model.reg.value directly

Wrap covergroups to increase flexibility

Use built-in test sequences for sanity checking

• Registers and memories