After a long break I finally got back to some homebrew coding. I worked in 6502 for a few hours today. I didn’t work on Explorer, but rather a different game project that is less ambitious. I’ll introduce the game properly in a future post.

What I Did Today

Button Combos

One thing that I needed for the new game project was a way to detect button combinations like up+A or right+B – the kind that you use to select plays in TecmoBowl. It was a little tricky to pull off. For one thing, if the player presses something like up+left+A, I need to resolve that to either up+A or left+A. I need to work that out for all possible combinations of button presses. This includes taking care of cases where A+B are pressed at the same time.

Another issue is with holding buttons. If the player holds B down and makes circles around the dpad, I only want it to catch the first combination. To do two combos in a row, they should release the B button and press it again. But what if the player hits up+B, and then while still holding B they press A+left? Does the holding of B stop the 2nd combination from being picked up or not? There are a lot of possible cases since the controller reading routine is called 60 times per second. The player can’t control their input on a frame-by-frame scale. Sliding from B to A might very well contain several frames (fraction of a second) where both buttons are held down before the B button is released. Not impossible to solve, but it wasn’t as straightforward as I had expected.

Sound Engine

Another thing I did today was port my sound engine to ca65. I wrote my NES sound tutorials for the NESASM assembler. My tutorials are a continuation of another set of tutorials which use NESASM and I wanted to stay consistent. Plus most new nesdevers start with NESASM as it is very newbie-friendly.

My tutorial sound engine was an improvement over the one I had previously written in ca65, so I wanted to replace the old with the new. So I spent some time today porting my sound engine from NESASM to ca65. I was sure everything was going to break as soon as I got all the syntax converted. But it didn’t! Once I got it to assemble it worked perfectly on the first try! That was a relief.

Scopes

ca65 lets you define scopes. Scopes enable you to keep parts of your program hidden from the other parts of your program. It’s good to separate modules, especially in large programs, so that you don’t have variable conflicts and the like. These bugs are the hardest to trace in assembly language.

I didn’t use scopes before because I didn’t really know how. But I found a great thread on nesdev about ca65 scopes that told me how to do it, so I spent some time today separating my sound and controller reading modules from the main program. Everything feels much … cleaner now. Like washing your hands after working outside on a summer day. I can physically feel how much easier things are going to be in the future for me with scopes.

New NES

I bought an NES! Ordered it on Yahoo Auctions on Saturday and it arrived at my house on Sunday! All I need now is a PowerPak and I can start testing my programs on real hardware. I can’t wait!

I’m too lazy to upload pictures here, but you can see the ones I posted to twitter here:

My new NES 1
My new NES 2