Importer

Importing OpenTitan hjson definitions can occur at any point alongside normal SystemRDL file compilation. When an OpenTitana hjson file is imported, the register description is loaded into the SystemRDL register model as if it were an addrmap component declaration. Once imported, the OpenTitan hjson contents can be used as-is, or referenced from another RDL file.

Since the target register used internally uses SystemRDL semantics, the import operation does a ‘best effort’ attempt to faithfully map the concepts described in OpenTitan hjson into SystemRDL objects.

Some of the properties in OpenTitan hjson do not exist in SystemRDL, and vice versa. In those cases a warning is printed during conversion and/or a sane conversion value is assumed.

Field swaccess and hwaccess fields

SystemRDL supports more sw and hw access properties than OpenTitan format. OpenTitan uses swaccess string property to describe the effect of software access to a field, to get the wanted behaviour in SystemRDL it is neccessary to use sw, onread, onwrite properties additionally. The table is shown next.

OpenTitan to SystemRDL swaccess properties

OT SW	Desc	RDL sw	RDL onwrite	RDL onread	Comment
none	No access	na			Invalid in SystemRDL
ro	Read Only	r
rc	Read Only, reading clears	r		rclr
rw	Read/Write	rw
r0w1c	Read zero, Write with 1 clears	rw	woclr		Read zero does not map to RDL
rw1s	Read, Write with 1 sets	rw	woset
rw1c	Read, Write with 1 clears	rw	woset
rw0c	Read, Write with 0 clears	rw	wzc
wo	Write Only	w

OpenTitan to SystemRDL hwaccess properties

hwaccess	Desc	hw
none	No access	na
hro	Read Only	r
hrw	Read/Write	rw
hwo	Write Only	w

API

Limitations

Unfortunately, not all OpenTitan hjson concepts are able to be faithfully translated into SystemRDL. The warning is supposed to be printed whenever such property is encountered in OpenTitan hjson.