NAME

srec_aomf - Intel Absolute Object Module Format

DESCRIPTION

The Absolute Object Module Format (AOMF) is a subset of the 8051 OMF. The structure of an absolute object file (the order of the records in it) is similar to that of a relocatable object file. There are three main differences: the first is that an absolute object file contains one module only, the second is that not all the records can appear in the absolute file and the third is that the records can contain only absolute information.

Generic Record Format

Each record starts with a record type which indicates the type of the record, and record length which contain the number of bytes in the record exclusive of the first two fields. The record ends with a checksum byte which contains the 2s complement of the sum (modulo 256) of all other bytes in the record. Therefore the sum (modulo 256) of all bytes in the record is zero.

The record length includes the payload and checksum fields, but excludes the type and length fields.

All 16‐bit fields are little‐endian.

REC TYP 8 bits

Record Length 16 bits

Payload

CHK SUM 8 bits

Here are some of the relevant record types:

0x01	Scope Definition Record
0x02	Module Start Record
0x04	Module End Record
0x06	Content Record
0x0E	Segment Definition Record
0x12	Debug Items Record
0x16	Public Definition Record
0x18	External Definition Record

Names are not stored as C strings. Names are stored as a length byte followed by the contents.

Structure

An AOMF file consists of a module header record (0x02), followed by one or more content (0x06), scope (0x01) or debug (0x12) records, and ends in a module end record (0x04).

The records with the following types are extraneous (they may appear in the file but are ignored): 0x0E, 0x16 and 0x18 (definition records). All records which are not part of the AOMF and are not extraneous are considered erroneous.

Module Header Record

REC TYP 0x02

Record Length 16 bits

Module Name

TRN ID 8 bits

zero 8 bits

CHK SUM 8 bits

Each module must starts with a module header record. It is used to identify the module for the RL51 and other future processors of 8051 object files. In addition to the Module Name the record contains:

TRN ID

The byte identifies the program which has generated this module:

0xFD	ASM51
0xFE	PL/M-51
0xFF	RL51.

Module End Record

REC TYP 0x04

Record Length 16 bits

Module Name

zero 16 bits

REG MSK 8 bits

zero 8 bits

CHK SUM 8 bits

The record ends the module sequence and contains the following information: characteristics

MODULE NAME: The name of the module is given here for a consistency check. It must match the name given in the Module Header Record.
REGISTER MASK (REG MSK)

The field contains a bit for each of the four register banks. Each bit, when set specifies that the corresponding bank is used by the module:

Bit 0 (the least significant bit): bank #0.
Bit 1: bank #1.
Bit 2: bank #2.
Bit 3: bank #3.

Content Record

REC TYP 0x06

Record Length 16 bits

SEG ID 8 bits

Offset 16 bits

DATA

CHK SUM 8 bits

This record provides one or more bytes of contiguous data, from which a portion of a memory image may be constructed.

SEG ID: This field must be zero.
OFFSET: Gives the absolute address of the first byte of data in the record, within the CODE address space.
DATA: A sequence of data bytes to be loaded from OFFSET to OFFSET+RECORDLENGTH−5.

Size Multiplier

In general, raw binary data will expand in sized by approximately 1.02 times when represented with this format.

SOURCE

http://www.intel.com/design/mcs96/swsup/omf96_pi.pdf
ftp://download.intel.com/design/mcs51/SWSUP/omf51.exe (zip archive)
http://www.elsist.net/WebSite/ftp/various/OMF51EPS.pdf

COPYRIGHT

The srec_cat program comes with ABSOLUTELY NO WARRANTY; for details use the 'srec_cat -VERSion License' command. This is free software and you are welcome to redistribute it under certain conditions; for details use the 'srec_cat -VERSion License' command.

MAINTAINER

Scott Finneran	E‐Mail:	scottfinneran@yahoo.com.au
Peter Miller	E‐Mail:	pmiller@opensource.org.au