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ROM Partitioning
C.1 Firmware EPROM Layout
Figure C–1 KA681/KA691/KA692/KA694 FEPROM Layout
Branch Instruction
System ID Extension
PC$MSG_OUT_NOLF_R4
CP$READ_WITH_PRMPT_R4
Rsvd Mfg L200 Testing
Def Boot Dev Dscr Ptr
Def Boot Flags Ptr
Console, Diagnostic,
and Boot Code
EPROM Checksum
Reserved for Digital
4 Pages Reserved
for Customer Use
20040000
20040006
20040008
2004000C
20040010
20040014
2004001c
2005F800
2005FFFC
MLO-007698
The first instruction executed on halts is a branch around the System ID
Extension (SIE) and the callback entry points. This allows these public data
structures to reside in fixed locations in the FEPROM.
The callback area entry points provide a simple interface to the currently
defined console for VMB and secondary bootstraps. This is documented further
in the next section.
The fixed area checksum is the sum of longwords from 20040000 to the
checksum inclusive. This checksum is distinct from the checksum that the rest
of the console uses.
The console, diagnostic and boot code constitute the bulk of the firmware.
This code is field upgradable. The console checksum is from 20044000 to the
checksum inclusive.
The memory between the console checksum and the user area at the end of
the FEPROM is reserved for Digital for future expansion of the firmware. The
contents of this area is set to FF.
The last 4096 bytes of FEPROM are reserved for customer use and are not
included in the console checksum. During a PROM bootstrap with PRB0 as the
selected boot device, this block is tested for a PROM "signature block".
C–2 ROM Partitioning