!Field

The !Field tag declares a single field within a !Reg or !Inst declaration, providing a way to split the full width of register up into meaningful sub-divisions. It’s very useful for packing multi pieces of related information into a word that’s retrievable with a single fetch.

Placement of the !Field within the register’s width can be controlled by using the lsb (least-significant bit) and msb (most-significant bit) parameters. If both parameters are omitted then the field will be placed with its least-significant bit at the first available position, following the order that the !Fields have been declared in the !Reg or !Inst tag’s field list.

Where a field is used to represent a discrete value, it can be enumerated using !Enum tags - allowing a name to be associated with a particular value, along with a description of its purpose.

Usage

The !Field tag is relatively primative, so can be used with either sequence or mapping syntax - although the value cannot be enumerated when using sequence syntax. Examples of both forms are given below.

- !Reg
  name  : status
  width : 32
  fields:
  - !Field [uptime, 24, 0, U, 0, "How many seconds system has been up"]
  - !Field
    name : state
    width: 1
    lsb  : 24
    sd   : Current system state
    reset: 0
    enums:
    - !Enum [inactive, 0, "System has not been configured"]
    - !Enum [active,   1, "System is ready to receive data"]
  - !Field
    name : mode
    width: 4
    msb  : 31
    sd   : Mode of operation
    reset: 0
    enums:
    - !Enum [idle,     0, "Waiting for next instruction"]
    - !Enum [transmit, 1, "Currently transmitting data"]
    - !Enum [receive,  2, "Currently receiving data"]
    ...
class blade.schema.ph_field.Field(name, width='-', lsb=None, type='-', reset='-', ld='', sd='', msb=None, enums=None, options=None, enum=None)

Defines a field within a register with name, width, type, and optional enumeration of the value.

__init__(name, width='-', lsb=None, type='-', reset='-', ld='', sd='', msb=None, enums=None, options=None, enum=None)

Initialisation for the !Field tag

Parameters

  • name – The name of the field

  • width – How many bits wide it should be

  • lsb – Least significant bit, controls placement within the register

  • type – Whether the field holds a signed or unsigned value

  • reset – The value that should be taken at reset

  • ld – Long description of the field - no maximum length

  • sd – Short description of the field - maximum 150 characters

  • msb – Most significant bit, alternative placement within the register

  • enums – List of enumerated values using !Enum tags

  • options – List of optiosn either in the form ‘KEY=VALUE’ or just ‘KEY’ if a value is not required.

  • enum – Alternative to ‘enums’

set_file_marks(start, end)

Set start and end marks of the declaration and propagate to children

Parameters

  • start – The starting mark

  • end – The ending mark

set_source_file(file)

Set the source file of this object and propagate it to children.

Parameters

file – The source file path or object

validate()

Check that this tag agrees with our YAML schema