Parameter Passing

The structure for representing the parameters has several requirements:

• It should identify the type of data being passed, to allow for translation between its standard format and the format desired by the stream processor selected for execution.
• It should support parameters with large bit sizes (up to 64 bits, at least.)
• It should be compact, to minimize transmission latency over slow communications channels.

These requirements strongly suggest the use of a tagged, variable length data word to represent each parameter. To simplify the software task of translating the standard format into the processor specific one, the size of the data word must be a multiple of eight bits (referred to hereafter as a byte.)

Parameter Word Representation

The first byte of the parameter word is a tag containing both a four bit parameter type field, and four bits indicating the number of bytes of data in the parameter word. The parameter words are located in memory with the byte containing the tag in the lowest memory address, following by the least significant byte of the data word in the next higher address.

Parameter List Representation

The parameters are passed as a list, started with a size field specifying the number of bytes in the parameter list (not including the size field). The size field utilizes one byte, limiting the parameter list to at most 255 bytes of parameters. This allows up to fifty 32-bit parameters, or fifteen 128-bit parameters, to be specified.

• Predefined Parameter Types
• Caller Software Interface
• Passing of Parameters to Software Functions
• Passing of Parameters to Hardware Functions