Uniform Driver Interface: Difference between revisions

Metalanguages define extensions to the core specification for various purposes, and can also be used to define custom IPC protocols between modules/regions. An example of a case where a custom protocol may be needed is where, for example, a network card driver has a "'''Control'''" region which takes commands from the kernel for power management ("Go to sleep", "prepare to shutdown", etc), and then it has a '''Send'''() region and '''Receive'''() region, which handle its send() and receive() functions respectively.

It follows naturally that if the driver receives a "Go to sleep" command from the kernel on its Control region, it would need to send messages to its Send and Receive regions to cause them to cease operation. There is no generic IPC_Send() function defined for IPC across UDI channels -- all IPC must be done according to the protocols APIs defined by a Metalanguage, whether standardized by the UDI spec, or custom-defined. Thankfully, driver writers do not need to define custom protocols for every such case where they want to simply send custom messages between regions: the UDI Core specification defines a "'''Generic I/O Metalanguage'''" IPC protocol which covers a wide range of generic IPC needs and can be extended with custom messages as desired.

Apart from IPC protocols, Metalanguages also cover extensions to the core specification. For example, the already-defined UDI Bus/Bridge Metalanguage can be extended to support new buses as needed; PCI bus drivers, ISA bus drivers, etc do not all need new Metalanguages, because UDI has defined a core UDI Bus/Bridge Metalanguage. This core UDI Bus/Bridge Metalanguage can be extended using Bus/Bridge Metalanguage extensions specific to each bus. This is a case where a Metalanguage is already defined by the UDI Standard, and that metalanguage itself is extended as needed for each bus.

Entirely new Metalanguages can also be created where necessary; for example, an SCSI Host Bus Adapter is not really a bus, but it is an I/O Microcontroller device that acts as a parent device to SCSI devices (mostly disks). It looks like a bus, but isn't really a bus, and is better handled with an IPC protocol and API of its own. So the UDI specification defines an SCSI Host Bus Adapter Metalanguage which manages communication (IPC) between SCSI Peripheral Devices (disks) and SCSI Host Bus Adapters. On any given motherboard, a commonly seen arrangement may be as follows in the ASCII art below. The SCSI HBA is not a bus, and the IPC communication between SCSI disks and the SCSI HBA cannot be constrained to follow the same format as communication between a bus and its child devices. This is a case where a new Metalanguage is a good idea.

Metalanguages are essentially UDI IPC Channel protocol definitions, and definitions of extensions to the core specification. Hence the name: Meta-''LANGUAGES''.