[BBC-Micro] Programatically "reset" a Beeb?

Richard Gellman splodge at starfleet-net.co.uk
Wed Aug 15 13:44:50 BST 2012



I'm having trouble with a "reset" process. Hopefully someone
here can point out the Bleeding Obvious(tm) to me. 

I've build a board
for my M128 with two ROM sets, the original M128 set and the Model B
OS1.2/Basic2 ROMs. Switching between them is under software control.

Obviously, one do not simply change ROMs. So my procedure is thus:

Disable interrupts (SEI) 

Store 0 at ROMSEL (fe30) and ACCCON (fe34)
to enable B-like memory mapping. 

Store the bit in the ROM set select
register (1MHz bus) 


Except, it doesn't quite work. It
changes ROM set sure enough, but the start sequence is interrupted and
scrolls uncontrollably, sometimes with characters on screen. 

I tried
blanking the 32K RAM beforehand, setting it all to &FF, and use of
*FX200,3 but none worked. I'm clearly missing a clue on how to reset the
state of the machine so it can start properly. 

Any suggestions as to
what I'm missing? 


-- Richard 

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