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32Re: [cosmacelf] Space Invaders

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  • Dave Ruske
    Mar 2, 2002
      Sounds like a nice piece of work, Charlie! I presume you were using the 1861
      for graphics?

      TinyELF (the emulator for the Palm OS) could probably run the code, depending
      on what you used for game control. One shortcut I took in TinyELF was the use
      of regular button objects for the hex keypad --- and the side effect is that
      while one of those buttons is pressed, 1802 code execution is effectively
      paused while the Palm OS sits and spins. I did something special for the
      Input key (programmed it using a gadget) so that one doesn't exhibit that
      behavior. I keep meaning to get back to TinyELF's code to add some features
      (such as a sorely-needed program import), but as priorities go that project
      usually gets trumped.

      The other, more obvious, problem with TinyELF is that it *crawls*. You'd
      think that emulating a 1.79 MHz 8-bit machine on a 20+ MHz Dragonball would
      be quicker, but in practice the code needs to do a lot of cycle counting to
      properly emulate the Pixie graphics. When Palm comes out with their 200 MHz
      ARM handhelds, I think TinyELF may be able to approach the speed of a real

      Bill Richman's emulator (the one I think you refer to) may run the code, but
      it depends... last time I played with it, the STXD instruction didn't work,
      and I don't believe that emulator has been updated. As I recall, the
      instruction did the store-via-X but didn't decrement afterwards. If you're
      using X as a stack pointer while running a virtual 1861, there's no easy fix
      for this. Adding a decrement alone wouldn't work, because an interrupt could
      hit between the STX and the DEC and nail the stack.

      By the way, let me know if you'd like to make your Space Invaders game
      available to others. I've just recently created a software area on
      cosmacelf.com, and I'd welcome any such contributions.


      On Saturday 02 March 2002 08:30 pm, you wrote:
      > Hi group, I'm a newbie here. I have an awesome Space Invaders game
      > that I wrote about 20 years ago for the ELF II. Full graphics and
      > gameroom action and all. It even makes Q click when you hit suff! (If
      > you were one of those folks who pu a speaker on Q). I still have
      > machine readable source code for it (actually the code exists on a
      > mainframe where my 1802 cross-assembler lives). I want to run this
      > code again but my actual ELF hardware is somewhat less than operative.
      > What's the status of emulators for ELF II? (I know there is the
      > original ELF emulator complete with toggles but is needs the 4k
      > expansion card etc...) Anyone got an interest in this?
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