Integrating RAL with the Environment

How to connect the abstract Register Model to the physical Bus Sequencer using Adapters and Predictors.

The Register Adapter

The adapter is a bridge. It converts a Generic Register Transaction (`uvm_reg_bus_op`) into a Bus Specific Sequence Item (e.g., `ahb_item`), and vice versa.


class my_adapter extends uvm_reg_adapter;
   virtual function uvm_sequence_item reg2bus(const ref uvm_reg_bus_op rw);
      ahb_item pkt = ahb_item::type_id::create("pkt");
      pkt.addr = rw.addr;
      pkt.data = rw.data;
      pkt.write = (rw.kind == UVM_WRITE);
      return pkt;
   endfunction
   virtual function void bus2reg(uvm_sequence_item bus_item, ref uvm_reg_bus_op rw);
      ahb_item pkt;
      $cast(pkt, bus_item);
      rw.addr = pkt.addr;
      rw.data = pkt.data;
      rw.kind = pkt.write ? UVM_WRITE : UVM_READ;
   endfunction
endclass

Connecting in Environment

In the `connect_phase` of your Environment (or Agent), you must link the Register Map to the Sequencer and Adapter.


function void connect_phase(uvm_phase phase);
    // 1. Set the sequencer for the default map
    reg_model.default_map.set_sequencer(agent.sqr, adapter);
    // 2. Connect Predictor (Explicit prediction)
    predictor.map = reg_model.default_map;
    predictor.adapter = adapter;
    agent.monitor.ap.connect(predictor.bus_in);
endfunction

Implicit vs Explicit Prediction (Interview Essential)

Frequently Asked: "What's the difference between implicit and explicit prediction in RAL?"

Mode	How Mirror Updates	Pros	Cons
Implicit (Auto)	After `reg.write()` completes	Simple setup	Misses external writes
Explicit (Predictor)	Monitor observes transactions	Catches all bus activity	Requires predictor setup

Setting Prediction Mode


// IMPLICIT (Auto) - RAL updates itself after write()
reg_model.default_map.set_auto_predict(1);
// EXPLICIT (Recommended) - Predictor watches the bus
reg_model.default_map.set_auto_predict(0);
// Requires: predictor.map = reg_model.default_map;
//           agent.monitor.ap.connect(predictor.bus_in);

Production Recommendation

Use Explicit Prediction in production environments. It catches writes from other masters, DMA engines, and hardware-triggered updates that implicit prediction would miss.

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