splendidnut's Blog

Awesome! I am one of those that actually liked M-Network's efforts, so a better version has me very excited. I loved how only the hotdog would straight persue you. That is until you finished all five screens. Then the breadstick would join the hotdog in aggressive tactics. All that really means is they don't turn at every ladder.

M-Network (Ron Surratt, specifically) actually did a really good job with it. The display engine of the original was as crammed as it could be. The extra RAM they had in the cartridge was used for storing the game variables since the main RAM in the Atari was almost completely used by the display engine; mainly for the burgers. The extra RAM/bankswitching also made it easy to make it a two player game. There really was no way they could make it better at the time.

 

My original idea was to finesse their engine, but that would have been way too much work. I started without using any special bankswitching, but soon gave up and switched to using DPC. Which worked for the most part, but didn't quite have the power needed for really improving the burgers. To display the burgers with differentiating colors requires 8 TIA updates per burger display line. With DPC handling the sprites, I had something working that just fit within a display line and updated at least the colors (4 of the 8 TIA updates). I didn't have enough time left to also update the playfield display of the burgers for showing them being knocked by the Chef.

 

If I really wanted to, I probably could have come up with some way to do it... I had that bouncing around in the back of my mind since August... but then November came around and nothing had come to me, so I had to come up with some other idea.

 

I started digging around and hit upon the DPC+ Demo. I remember reading about the bus-stuffing capabilities back during the summer. It sounded cool... then when I saw the demos, it really hit me how much power it would give me. One of the big benefits outside of the 10 cycle TIA writes was the ability to write back to display RAM... which should give me everything I need to really make it work and look good. Maybe even make the burger pieces look like real pieces on the level.

I started digging around and hit upon the DPC+ Demo. I remember reading about the bus-stuffing capabilities back during the summer. It sounded cool... then when I saw the demos, it really hit me how much power it would give me. One of the big benefits outside of the 10 cycle TIA writes was the ability to write back to display RAM... which should give me everything I need to really make it work and look good. Maybe even make the burger pieces look like real pieces on the level.

In DPC you can update a TIA register in 7 cycles:

  LDA DF0DATA ; 4
  STA GRP0 ; 3

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In DPC+ we added an immediate mode override, called Fast Fetch, that lets you do the same in 5 cycles:

  LDA #<DF0DATA ; 2
  STA GRP0 ; 3

---

Bus Stuffing would override a store to zero page, for a 3 cycle update, like this:

  STY GRP0 ; 3 

---

DPC+ doesn't use bus stuffing. For more info on that check these two topics:

• "Bus stuffing" like The Graduate.
• Bus Stuffing Demos

Ah yes... Fast Fetching not "bus stuffing"... Fast Fetch overrides the immediate load by substituting the value being passed from the Harmony memory to the CPU (6507); whereas, bus stuffing overrides the data sent from the CPU (6507) to the Atari 2600 TIA chip.

 

And to clarify, by 10 cycle TIA writes I meant 10 cycles to write both color and PF data.

 

Thanks for catching that SpiceWare.