a61cbe6f   
   From: alawther@spammenot.mac.com   
      
   Anthony Ortiz  wrote:   
   > On Tuesday, August 16, 2022 at 7:48:21 PM UTC-4, Anthony Lawther wrote:   
   >> If the Pi is snooping every phase of every bus cycle you could copy the   
   >> interfaces of standard peripheral cards (Uthernet II for IP, SSC for   
   >> printers, video phase of the data bus for native video) and then maybe   
   >> Smartport for storage and any new facilities you want to add. By allowing   
   >> the one card to logically appear in multiple slots (user programmed e.g.   
   >> Uthernet II in Slot 1, SSC in Slot 2, Mouse card in Slot 4, Smartport in   
   >> Slot 5, Disk ][ in Slot 6) backed by emulated peripherals on the Pi you   
   >> could tap into much of the existing software base and only need to create   
   >> new Apple software to take advantage of the new features.   
   >>   
   >> With the user programming of functions to slots, you could even have a   
   >> helper program in the Apple interrogate the slots for physical cards and   
   >> disallow use of occupied slots to avoid bus contention. If you want to get   
   >> really adventurous you could require your card be placed in Slot 7 and have   
   >> it subvert the boot process by appearing as a boot device, pushing the   
   >> helper program to system RAM as a boot block, interrogating the slots to   
   >> identify physical cards, allow the user to decide how to manage any   
   >> conflicts detected, and then continue the boot process as normal. That   
   >> would slow down every boot, so it might be something you’d want to be able   
   >> to disable or only perform when a certain key combination is detected.   
   >   
   > Wow, these are some great ideas! I really like making it logically   
   > appearing in multiple slots and leveraging existing code, and I had no   
   > idea slot 7 could be used that way... You've given me a lot to think about,   
   thank you!   
   >   
      
   I suggest Slot 7 because it is polled first in the boot sequence. There are   
   some signals that are only connected to Slot 7, but every slot has the full   
   buffered address bus, data bus, R/W’, and clocks. The capability needs to   
   come from the Pi watching the buses and managing the interactions with the   
   Apple.   
   If people had a card sitting in Slot 7 that made use of the extra signals   
   (mostly relevant to video) then that card would most likely not have the   
   ROM signature of a boot device and with your card in Slot 6 the same boot   
   subversion approach could work.   
   Another thing to note is that Slot 7 is last in the DMA and interrupt   
   priority chains. If you haven’t looked at Jim Sather’s ‘Understanding the   
   Apple IIe’ then I highly recommend it. Chapter 7 gives a thorough look at   
   the card slots.   
      
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