user manual

ROMboot
B-5
B
At power-up, the tape controller positions the streaming
tape to load point where the volume ID can correctly be
read and used.
If, however, the MVME177 loses power but the
controller does not, and the tape happens to be at load
point, the sequences of commands required (attach and
rewind) cannot be given to the controller and autoboot
will not be successful.
ROMboot
The ROMboot function is configured/enabled by the Environment
(ENV) command (refer to Commands Table at the end of this
Appendix) and executes:
❏ At power-up
❏ At reset (optionally)
❏ By the RB command, assuming there is valid code in the
EPROMs (or optionally elsewhere on the module or
VMEbus) to support it.
If ROMboot code is installed, a user-written routine is given control
(if the routine meets the format requirements). One use of
ROMboot might be resetting SYSFAIL* on an unintelligent
controller module. The NORB command disables the function.
For a user's ROMboot module to gain control through the
ROMboot linkage, four requirements must be met:
❏ Power must have just been applied (but the ENV command
can change this to also respond to any reset)
❏ Your routine must be located within the MVME177 ROM
memory map (but the ENV command can change this to any
other portion of the onboard memory, or even offboard
VMEbus memory)