user manual

Autoboot

B-3

177Bug Implementation

MVME177Bug is written largely in the ÒCÓ programming

language, providing benefits of portability and maintainability.

Where necessary, assembler has been used in the form of separately

compiled modules containing only assembler code - no mixed

language modules are used.

Physically, 177Bug is contained in two 44-pin PLCC/CLCC

EPROMs, providing 512KB (128K longwords) of storage. Both

EPROMs are necessary regardless of how much space is actually

occupied by the firmware, because of the 32-bit longword-oriented

MC68060 memory bus architecture. The executable code is

checksummed at every power-on or reset firmware entry, and the

result (which includes a pre-calculated checksum contained in the

EPROMs) is tested for an expected zero. Thus, users are cautioned

against modification of the EPROMs unless re-checksum

precautions are taken. The power-on defaults for the MVME177

debug port are:

❏ Eight bits per character

❏ One stop bit per character

❏ Parity disabled (no parity)

❏ Baud rate 9600 baud (default baud rate of MVME177 ports at

power-up)

After power-up, the baud rate of the debug port can be

reconfigured by using the Port Format (PF) command of the 177Bug

debugger.

Autoboot

Autoboot is a software routine that is contained in the several

177Bug EPROMs to provide an independent mechanism for

booting an operating system. This autoboot routine automatically

scans for controllers and devices in a specified sequence until a

valid bootable device containing a boot media is found, or the list is