For writing entire functions in ASM, as well as more complex projects, it can be preferable to write external assembly files.

In the Wonderful toolchain, these files use the .s extension and are compiled using the GNU assembler and the C preprocessor.

It is recommended to start with a preamble similar to the following:

#include <wonderful.h> // (1)!
#include <ws.h> // (2)!

    .code16 // (3)!
    .arch i186 // (4)!
    .intel_syntax noprefix // (5)!

1. Include the Wonderful toolchain's basic definitions. This provides some useful assembly defines and macros.
2. Include the libws library's definitions. This library supports being included in an assembler, and provides hardware-related defines. You may wish to skip this line if targetting the WonderWitch.
3. Tell the assembler to emit 16-bit code; this is useful as the GNU assembler supports all kinds of x86 code, including 32-bit and 64-bit.
4. Tell the assembler to emit 80186 code; this unlocks some additional 80186-exclusive opcodes supported on the NEC V30MZ
5. Tell the assembler to emit Intel-syntax assembly; this is entirely optional, but the examples for external assembly files in this guide all make use of the Intel syntax, as opposed to the AT&T syntax used in inline assembly.