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Metadata specifies static properties pertaining to the interaction between:
- A Controller and its hosting hardware.
- An AIM and its hosting Controller.
- A Composite AIM and its component AIMs.
Metadata specified in the following Sections is represented in JSON Schema.
| 1 Communication channels and their data types | 2 AIF Metadata |
| 1.1 Type system | 3 AIM Metadata |
| 1.2 Mapping the type to buffer contents |
1 Communication channels and their data types
This Section specifies how Metadata pertaining to a communication Channel is defined.
1.1 Type system
The data interchange happening through buffers involves the exchange of structured data.
Message data types exchanged through Ports and communication Channels are defined by the following Backus–Naur Form (BNF) specification [10]. Words in bold typeface are keywords; capitalised words such as NAME are tokens.
| fifo_type := | /* The empty type */ | base_type NAME recursive_type := | recursive_base_type NAME base_type :=| toplevel_base_type| recursive_base_type| ( base_type )toplevel_base_type := | array_type| toplevel_struct_type| toplevel_variant_typearray_type :=| recursive_base_type [] toplevel_struct_type := | { one_or_more_fifo_types_struct }one_or_more_fifo_types_struct := | fifo_type | fifo_type ; one_or_more_fifo_types_structtoplevel_variant_type := | { one_or_more_fifo_types_variant }one_or_more_fifo_types_variant := | fifo_type | fifo_type | fifo_type | one_or_more_fifo_types_variant recursive_base_type :=| signed_type| unsigned_type| float_type| struct_type| variant_typesigned_type :=| int8 | int16 | int32 | int64 unsigned_type :=| uint8 | byte | uint16 | uint32 | uint64float_type := | float32 | float64 struct_type := | { one_or_more_recursive_types_struct }one_or_more_recursive_types_struct := | recursive_type | recursive_type ; one_or_more_recursive_types_structvariant_type := | { one_or_more_recursive_types_variant }one_or_more_recursive_types_variant := | recursive_type | recursive_type | recursive_type | one_or_more_recursive_types_variant |
Valid types for FIFOs are those defined by the production fifo_type.
Although this syntax allows to specify types having a fixed length, the general record type written to, or read from, the Port will not have a fixed length. If an AIM implemented in hardware receives data from an AIM implemented in software the data format should be harmonised with the limitations of the hardware AIM.
1.2 Mapping the type to buffer contents
The Type definition allows to derive an automated way of filling and transmitting buffers both for hardware and software implementations. Data structures are turned into low-level memory buffers, filled out by recursively traversing the definition (breadth-first). Sub-fields are laid down according to their type, in little-endian order.
For instance, a definition for transmitting a video frame through a FIFO might be:
| {int32 frameNumber; int16 x; int16 y; byte[] frame} frame_t |
and the corresponding memory layout would be:
[32 bits: frameNumber | 16 bits: x | 16 bits: y | 32 bits: size(frame) | 8*size(frame) bits: frame].
API functions are provided to parse the content of raw memory buffers in a platform- and implementation-independent fashion (see Subsection 8.3.7).
2 AIF Metadata
AIF Metadata specifies the AIF Metadata in terms of JSON Schema definition.
3 AIM Metadata
AIM Metadata specifies static, abstract properties pertaining to one or more AIM implementations, and how the AIM will interact with the Controller.
AIM Metadata specifies the AIM Metadata in terms of JSON Schema definition.
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