D

evices are the mechanism by which an application running in the context of a MASCOT Machine integrates with and accesses services supplied by the underlying

host hardware and software. Devices in MOJO have a factory behavior, ie. they manufacture and maintain device instances. Opening a device results in the caller being handed a pair of channels (read and write) by which he may access a specific instance of a device.

As with other MASCOT entities, device instances are named. The syntax of the open is as follows:

Object[] open( String deviceName, String deviceInstanceName );

DeviceName is what it says, the device’s MASCOT name. DeviceInstanceName is the local name by which the caller refers to the instance and can be used as an argument to resolve(). It is thus possible for activities to share access to a device instance by name; the first open creates the instance, subsequent opens will receive references to the channel pair associated with the named instance. The device code manages and maintains instance names and their associated incarnations.

MOJO devices present some unique coding challenges because, unlike other MASCOT subsystems, they are conceptually a mix of system and application specific code. As an aid to writing device handlers, MOJO implements the idea of worker activities which allow the definition and incarnation of generic system activities. Workers are not part of the normal SET syntax; developers can use them to implement system activities that essentially extend the functionality of the MASCOT machine. In many ways, workers analogous to operating system drivers.

Worker activities are MASCOT activities that do not have a specific subsystem container and may be incarnated within any subsystem context.   Developers  can  use