srec_aomf(5)

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 a 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