File Formats

Generic file format
Object file format

Generic file format

The Assembler can generate three different output file formats:

Generic
Motorola S-Records
Intel Intellec 8/MDS

The formats of the latter two are assumed known. The Generic file format is a simple, self defined format, where each line has the following format:

ADR:OPCODE

Where ADR is a 6 digit (24 bit) hexadecimal number and OPCODE is a 4 digit (16 bit) hexadecimal number. ADR defines an address in the Program memory, and OPCODE defines the contents of this address.

Example

Given the following assembly file gen_demo.asm:

; Demonstration of the Generic file format
        mov r0,r1
        inc r1
        call oursub
.org 0x50                 ; Set Program space
                          ; address to 50 (Hex)
oursub: add r1,r2         ; Do something
ret

Then the following output file gen_demo.rom will be produced:

000000:2c01
000001:9413
000002:940e
000003:0050
000050:0c12
000051:9508

Note that the two-word instructions (CALL and JMP) need two lines of coding.

Object file format

The object (.obj) file produced by the Assembler is also represented in a self defined format. The object file contains some limited debug information, and can be used together with AVR Studio

The object file has a header section, a record section and a trailer section. The header section has the following format:

Offset to source file names (4 bytes)
Offset to object records (4 bytes)
Number of bytes in each record (1 byte)
Number of file names stored in the Trailer (1 byte)
The string “AVR Object File\0” (\0 means zero terminated)

The records are currently 9 bytes long. Each record has the following format:

Program memory address (3 bytes)
Opcode (2 bytes)
Source file number of the instruction (1 byte, first file numbered 0)
Line number in the source file (2 bytes, first file numbered 1)
Macro indicator (1 byte, 1 if instruction is in a macro, 0 if not)

Finally, the trailer section has the following format:

File names (Zero terminated, number of file names in header)
ASCII 0

Example

Given the following assembly file obj_demo.asm:

; Demonstration of the Object file format (obj_demo.asm)
.equ const1=0x15
.equ const2=0x40
.macro SWIN               ; SWIN - swap and increment
        swap @0
        inc @0
.endmacro                 ; End macro
start: ldi r16,const1
        SWIN r16          ; Call macro
        ldi r16,const2
        SWIN r16          ; Call macro
        rjmp start
.include "delay.asm"      ; Include another assembly file delay.asm

; Include file, demonstration of the Object file format
; (delay.asm)
delay: dec r16           ; Decrement counter
        breq delay        ; If not zero branch to delay
        ret               ; Return from subroutine

Then the following output file obj_demo.obj would be produced (the file is a binary file which has been converted into hexadecimal representation, the offset column and the line shifts are manually inserted for reasons of clarity):

Offset:         File contents:                        Comment:
00000000:       00000074                              Offset to file names
00000004:       0000001A                              Offset to records
00000008:       09                                    #Bytes/record
00000009:       02                                    #File names
0000000A:       415652204F626A6563742046696C6500      AOF string
0000001A:       000000E10500000B00                    First record
00000023:       000001950200000C01
0000002C:       000002950300000C01
00000035:       000003E40000000D00
0000003E:       000004950200000E01
00000047:       000005950300000E01
00000050:       000006CFF900000F00
00000059:       000007950A01000400
00000062:       000008F3F101000500
0000006B:       000009950801000600                    Last record
00000074:       4F424A5F44454D4F2E41534D00            “OBJ_DEMO.ASM\0”
00000081:       44454C41592E41534D00                  “DELAY.ASM\0”
0000008B:       00                                    End of object file