I’m still not completely happy with the mockingboard implementation but one can play with it and if it doesn’t work nicely just turn it off (it’s off per default).
Skyfox starts playing music but hangs later which doesn’t happen when the mockingboard is turned off. Another bug is that from time to time I just hear statics and a new recompilation under Quartus fixed that. So something with the timing might not be okay. I’ve added a .sdc file which made it a little bit more stable but I’m open for hints on how to stabilize it.
I fixed another issue which annoyed me lately. When doing a reset the Apple II preserves it memory and software is able to alter the reset vector. At memory $3F2 and $3F3 the reset address is stored and when altered a reset brings you to the prompt (at best) or just hangs somewhere and you can only turn off the MiST. If $3F4 would be a random value and not the XOR between $A5 and $3F3 the Apple II would “think” its a cold boot and starts the Autostart ROM.
I just set $3F4 to zero when the cold boot option in the osd is pressed and the Apple II resets and tries to start from disk.