Motorola MVME147 Installation And Use Manual page 160

Debugger General Information
B
Module
Offset
$00
$04
$08
$0C
B-6
The format of the beginning of the routine is as follows:
Length Contents
4 bytes BOOT
4 bytes Entry Offset
4 bytes Routine Length Longword, includes length from
? Routine Name
By convention within Motorola, the checksum is placed in the two
bytes following the routine.
If you wish to make use of ROMboot you do not have to fill a
complete ROM. Any partial amount is acceptable, as long as the
length reflects where the checksum is correct.
ROMboot searches for possible routines starting at the start of the
memory map first and checks for the ÒBOOTÓ indicator. Two
events are of interest for any location being tested:
1. The map is searched for the ASCII string ÒBOOTÓ.
2. If the ASCII string ÒBOOTÓ is found, it is still undetermined
whether the routine is meant to gain control. To verify that
this is the case, the bytes starting from the beginning of
ÒBOOTÓ through the end of the routine (as defined by the
4-byte length at offset $8) are run through the checksum
routine. If both the even and odd bytes are zero, it is
established that the routine was meant to be used for
ROMboot.
Under control of the RB command, the sequence of searches for
ÒBOOTÓ is as follows:
1. Search direct address (as set by the RB command).
2. Search your non-volatile RAM (first 1KB of battery back-up
RAM).
3. Search complete ROM map.
Description
ASCII string indicating possible routine.
Longword offset from ÒBOOTÓ.
module offset $00 to and including
checksum.
ASCII string containing routine name.