Echelon Neuron - Manual (Page 58)

Overview
Typically, you use Neuron assembly language to create utilities that can be used
with an application that is written in Neuron C. The Neuron C program code
might call functions defined in Neuron assembly, or a Neuron assembly function
might call a Neuron C function or program.
This chapter describes the conventions that a Neuron assembly language
function must follow when interfacing with Neuron C functions, including data,
calling and naming conventions.
See the following sections for information about integrating, assembling, and
linking your assembly program with the Neuron C application: Integrating the
Program, Assembling the Program, and Linking the Program.
Naming Conventions
Within a Neuron assembly file, declare functions, variables, or any other linkable
item that interfaces with the Neuron C application, with a percent-sign prefix.
This declaration allows the symbol to become part of the Neuron C name space.
To make the symbol and its meaning available to the Neuron C application, you
must provide its C language ‘extern’ specification (for variables and constants) or
its prototype (for functions).
Within a Neuron C file, when you specify an external symbol, the Neuron C
compiler automatically assumes a percent-sign prefix.
Example:
The following example includes an assembly-coded function in a Neuron C
program:
#pragma include_assembly_file “checksum.ns”
extern unsigned Checksum(unsigned, const char*);
The compiler-generated calls to this function from the Neuron C application use
the name %Checksum. Thus, the assembly function must use the %Checksum
label with the APEXP directive:
%Checksum APEXP
... ; function body
ret ; return to caller
The Neuron C Compiler (and its companion tools, such as the Neuron Assembler
or Linker) cannot verify that the prototype (or extern specification that you
provide) actually matches the implementation in the assembly source file. It is
the programmer’s responsibility to ensure that the specification in Neuron C
matches the implementation in Neuron Assembly.
Function Parameters
Typically, an assembly language function is called with parameters. The
compiler pushes function arguments on the stack from right-to-left, so that the
last argument is in the TOS element of the stack. For example, for a function
with two arguments, such as Checksum(unsigned, const char*), the const char*
pointer is pushed first, and the unsigned argument is pushed into TOS.
48 Interfacing with a Neuron C Application