8 Interface; I N T R O D U C T I O N; T H E Message-Based Interface Software Architecture; Overview - Racal Instruments 7064 Instruction Manual

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SECTION 4

The Message-Based Interface has a simple and flexible software architecture that allows

users to load and execute their own application code in a variety of ways. Additionally,

the Message Based Interface provides several system services at the level of C-language

function calls. M a n y Message-Based Interface system configuration parameters are

programmable giving the user the ability to custom-tailor the Message-Based Interface for

a particular application.

Users may load many individually named blocks of application-specific code, and later

invoke selected blocks by name. The user may also load an application-specific command

parser which may also invoke these blocks, and Message-Based Interface system services.

It is advantageous t o users t o load and execute their own code f o r speed-critical

applications. B y doing so, the user's application can execute at full speed of the Message-

Based Interface's on-board Motorola 68000 microprocessor.

The Message-Based Interface has a single-threaded control-flow architecture. A l l

Message-Based Interface firmware runs in the supervisor mode, and utilizes the supervisor

stack pointer. After the initial power-up sequence, the Message-Based Interface command

parser gains control. I t loops endlessly, examining the character input stream for

Message-Based Interface commands.

Named blocks of executable application code may be loaded into a reserved memory area

of the Message-Based Interface address space. A t run time, these blocks may be invoked

by name. Syntactically, these invocations look like C-language function calls. Also, an

application-specific command parser may be loaded and invoked in two ways. First,

whenever the Message-Based Interface is waiting for input, it will make a function call

to the application parser rather than "busy wait" on input. When the machine is idle, the

application parser is repeatedly called. Second, the user may explicitly command the

Message-Based Interface to redirect the subsequent input stream to the application-specific

parser (the exact details of this maneuver are described in the section on Message-Based

Interface command syntax).

INTERFACE

4-1

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