Specifications

C–6 SROM Initialization
Subject to Change – 17 January 1997
Special ROM Header
Table C–2 describes each entry in the special header.
Table C–2 Special Header Entry Descriptions
Entry Description
Validation and inverse
validation pattern
This quadword contains a special signature pattern used to
validate that the special ROM header has been located. The
pattern is 5A5AC3C3A5A53C3C.
Header size (bytes) This longword provides the size of the header block, which
varies among versions of the header specification. When the
header is located, SROM code determines where the image
begins based on the header size. Additional data added to the
header is ignored by older SROM code. A header size of 32
bytes implies version 0 of the header specifications. For other
sizes, see Header revision to determine header version.
Image checksum This longword is used to verify the integrity of the ROM.
Image size The image size is used by the SROM code to determine how
much of the system flash ROM should be loaded.
Decompression flag The decompression flag informs the SROM code whether the
MAKEROM tool was used to compress the ROM image with a
repeating byte algorithm. The SROM code contains routines
that execute the decompression algorithm. Other compression
and decompression schemes, which work independently from
this scheme, may be employed.
Destination address This quadword contains the destination address for the image.
The SROM code loads the image at this address and begins
execution.
Header revision The revision of the header specification used in this header.
This is necessary to provide for changes to the header
specification. Version 0 headers are identified by the size of the
header (32 bytes). See Header size. For Version 1 or greater
headers, this field must be set to a value of 1. The header
revision for version 1 or greater headers is determined by the
sum of this field and the Header rev ext field. See Header rev
ext.