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Back-door access Methods

Back-door read/write vs. peek/poke

Back-door access to registers and memory by using the read/write methods with the path argument set to UVM_BACKDOOR.

  • uvm_reg_field::read() or uvm_reg_field::write()
  • uvm_reg::read() or uvm_reg::write()
  • uvm_mem::read() or uvm_mem::write()

There are also Peek/Poke methods that can be used instead

  • uvm_reg_field::peek() or uvm_reg_field::poke()
  • uvm_reg::peek() or uvm_reg::poke()
  • uvm_mem::peek() or uvm_mem::poke()

 

The peek() and poke() methods provide direct access to registers or memory using back-door access, but they behave differently compared to regular read() and write() methods:

  • peek() Method:
    The peek() method retrieves the raw value from a register or memory without altering its content. For example, if a register has a field that clears itself when read (like a clear-on-read field), using peek() will not trigger this behavior. This means the value obtained through peek() may differ from what you would get using the regular read() method.
  • poke() Method:
    The poke() method directly writes a value into a register or memory, overriding any field access restrictions. For instance, non-writable fields (like read-only or write1-to-clear fields) will still be forced to take the poked value, even if they wouldn’t normally accept it. This can lead to different results compared to writing through the regular front-door method.
  • read() with Back-Door Access:
    When using the read() method with back-door access, it behaves just like a front-door read. For example, if a register has a clear-on-read field, reading it will clear the field by automatically writing zeros to it (using a poke operation internally).
  • write() with Back-Door Access:
    Similarly, the write() method with back-door access mimics a front-door write. For example, if you try to write to a read-only field, the method will preserve the field’s current value by first retrieving it using peek() and then reapplying it using a poke() operation, instead of overwriting it with the specified value.