GASMIC Manual

General Syntax

This assembler follows a very uniform syntax akin to that of other assemblers.

[label:] [mnemonic [arguments]] [;comment]

GASMIC also supports various different instruction syntaxes. Namely, GASMIC aims to support Motorola, AT&T, and Intel syntaxes, and provides a pseudo instruction to select the correct syntax.

Motorola Syntax

Instructions logically support single arguments but are usually split to allow for simpler processing.
Registers are generally appended to the end of the instruction with few exceptions. (Example:
```
LDA
```
,
```
MOVEAX
```
)
Indexed addressing uses
```
[
```
and
```
]
```
.

AT&T Syntax

Instructions support multiple arguments.

Intel Syntax

Instructions support multiple arguments.
Registers have no prefix. (Example: eax, A)
Indexed addressing uses
```
[
```
and
```
]
```
.

Registers are prefixed by
```
%
```
. (Example: %eax, %A)
Indexed addressing uses
```
(
```
and
```
)
```
.

Expression Parsing

GASMIC supports arithmetic arguments. Calculations can be performed on a mix of integer constants and symbols. Evaluation follows the order of precedence as given in the following table. (higher in table means higher precedence).

Operation	Operator
Brackets	( )
Multiplication	*
Division	/
Addition	+
Subtraction	-
Bitwise XOR	^
Bitwise AND	&
Bitwise OR	\|

Integer Constants

Integer constants can be expressed in either base 10 or base 16, with plans to support base 2 and base 8.

Base	Prefix
10	No prefix
16	0x OR $
8	[Tentative] @
2	[Tentative] 0b or %

Symbols and Labels

Symbols can be global and local. A global symbol is an alphanumeric string ending with a colon. This string will then have the value of the current address unless it is immediately followed by the equ pseudo instruction.

Local labels can be specified by prefixing a label with a period (.). This label can then be referenced within the scope of the previous global label using the period notation, and can be reached from the global scope by prefixing the preiod notaion with the last global symbol.

Example

    .ORG 0xC000
print:
    LDX data.str
.loop:
    LDA ,X+
    BEQ .end
    STA 0x8000 ; example serial data output
    BRA .loop
.end:
    RTS

data:
.str: db 'Hello World', 10, 0

Pseudo Instructions

GASMIC supports several pseudo instructions to control metadata about the application. These instructions should be prefixed with a ., but to maintain compatibility, it is not required.

The list of available pseudo instructions and their purpose is described in the table below.

Pseudo Instruction	Description	Examples
ARCH	Set the architecture this application is targetting. Overrides the command line -m parameter. This pseudo instruction must come before any code.	.ARCH 6309 .ARCH z80
DB	Designate Byte. Assigns the following bytes in memory to the values passed as arguments. When a string is provided, sets the bytes to the ascii values of the characters. No escape characters are currently supported. numbers and strings can be mixed and matched.	.DB 0, 3, 2 .DB 'Hello' .DB 'Hello World', 10, 0
DW	Designate Word, Like DB , saves every number as a 16-bit word in the endianness of the selected architecture.. Strings are saved the same as if they were passed to DB .	.DW 0x1234
DD	Designate Double-word. Like DW , but for 32-bit double-words.	.DD 0x12345678
DQ	Designate Quad-word. Like DW and DD , but for 64-bit quad-words.	.DQ 0x1122334455667788
RESB	Reserve Bytes. Reserves n bytes.	.RESB 3 ; reserve 3 bytes
RESW	Reserve Words. Reserve n words, n * 2 bytes.	.RESW 5 ; reserve 5 words, 10 bytes
RESD	Reserve Double-words. Reserve n double-words, n * 4 bytes.	.RESD 2 ; reserve 2 double-words, 8 bytes
RESQ	Reserve Quad-words. Reserve n quad-words, n * 8 bytes.	.RESQ 1 ; reserve 1 quad-word, 8 bytes
EQU	Equate a label with an expression. The label will then have the value of the expression.	l1: .EQU 0x12 l2: .EQU l1 + 3 l3: .EQU 0xAA \| 0x55
INCLUDE	Include the file at the path provided as a string argument and assemble it as though it was inline.	.INCLUDE "path/to/file.inc"
INSERT	Inserts the raw bytes of the file at the path given as the string argument into the output file.	.INSERT "/path/to/some/file.jpg"
ORG	Origin of the program. The address where the program is intended to be loaded to.	.ORG 0x1234 ; all addresses will be relative to this point

GASMIC

Greg's Assembler (in C)

Table of Contents

Introduction