Autoboot

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

B

B-3

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Motorola MVME177 manual Autoboot, 177Bug Implementation