Bits And Registers

Registers describe addressable DUT state. Fields add names, access policies, reset values, and enumerations to bit ranges. Pattern code then operates on those semantic objects instead of assembling raw transactions repeatedly.

Bits

A field selects one or more bits within a register. Its offset is the least significant bit position and width defaults to one. Origen tracks data, verify masks, access policy, and reset information for the resulting bit collection.

Use field and register APIs to stage data before dispatching a transaction. The controller determines how the transaction reaches the DUT.

Registers

Simple Registers

Use SimpleReg when every bit shares the default behavior:

SimpleReg("control", 0x00)          # Defaults to 32 bits
SimpleReg("status", 0x04, size=16)

Registers declared without an explicit map are placed in the default memory map and default address block.

Fields

Use Reg as a context manager for field declarations:

with Reg("adc_cfg", 0x24, size=16):
    Field("complete", offset=7, access="ro")
    Field("irq_enable", offset=6)
    Field(
        "channel",
        offset=0,
        width=5,
        reset=0x1F,
        enums={
            "temperature": 3,
            "bandgap": {
                "value": 5,
                "usage": "w",
                "description": "Internal bandgap channel",
            },
        },
    )

Use access values such as ro only when the hardware policy differs from the default. Enumerations make patterns readable and centralize legal values.

Reset Values

reset defines the common hard-reset value. Use resets when a field has multiple reset domains or a partial reset mask:

with Reg("mode", 0x28, size=16):
    Field(
        "select",
        offset=0,
        width=5,
        resets={
            "hard": 5,
            "async": {"value": 0xF, "mask": 0b1010},
        },
    )

Memory Maps And Address Blocks

Use explicit scopes when a block has multiple buses or banks:

with MemoryMap("debug"):
    with AddressBlock("bank0"):
        SimpleReg("control", 0x00)

Names may be reused in different maps or address blocks. Code that relies on a non-default scope should use the fully qualified model path.

Transactions

Calling a register write or verify sends the modeled value, size, and address to the owning block controller. Keep bus sequences in the controller so the same register declarations can be reused by different DUT derivatives and testers.

Testing

Verify register size, field offsets, reset values, enum mappings, and absolute addresses. Include negative tests for overlapping fields, invalid values, and write attempts to read-only fields where the API enforces them.