Device Specification

3 Device Specification

device-spec	::=	device ident (device-params) { (object-def;)⁺ }
device-params	::=	device-param (, device-param)^*
device-param	::=	ident : type-expr port (@ { integer-ranges })^?
integer-ranges	::=	integer-range (, integer-range)^*
integer-range	::=	integer-literal
	\|	integer-literal .. integer-literal
object-def	::=	objdef
	\|	if (expr) objdef-body (else objdef-body)^?
objdef-body	::=	objdef
	\|	{ (objdef;)⁺ }
objdef	::=	register-definition
	\|	structure-definition
	\|	type-definition
	\|	variable-definition
	\|	unused-declaration

A device specification is introduced by the device keyword, and consists of an identifier, followed by a comma separated list of parameters, and then one or more Devil object definitions . Devil objects are register, structure, type or variable. The identifier is the name of the device being defined.

Device parameters

A device parameter named base specifies the number of bits that can be exchanged at the base address. The optional construct @ { integer-ranges } allows one to define a set of integer offsets that can be added to the base address in order to compute an other address with the same characteristics. Note that the device parameter definition

  base : bit[8] port

is equivalent to

  base : bit[8] port @ {0}

Conditional definitions

The expression if (expr) def-body₁ else def-body₂ allows one to conditionally define a Devil object. A Devil object cannot be re-defined; the same identifier cannot be used for several differents Devil objects, even if its definition is conditional. A definition in def-body₁ (respectively def-body₂) can be accessed at a time t if and only if the expression expr can be evaluated to true (respectively false) in the environment present at time t. The else def-body₂ part can be omitted, in which case it defaults to an empty definition.

Expressions of conditional definitions

The expression of a conditional definition is an expression where identifiers can refer to device parameters or variables. The expression is evaluated each time an access to a variable conditionally defined is performed. The identifier name of a read variable is evaluated to the previous value read. The identifier name of a write or read-write variable is evaluated to the previous value assigned to this variable. Moreover, code can be inserted in the generated interface in order to check if a variable has been previously read or written.