Following the SDRAM-related improvements to the Megadrive / Genesis core that I’ve covered in my last couple of posts, here’s an updated snapshot for both the Chameleon and MIST boards:
While it’s still not perfect, the glitches should be much less noticeable, and hopefully there will no more missing platforms or missiles making games unplayable!
Part 2: Saving cycles
In the first part of this series I covered some basic tidy-ups to the code to make it easier to maintain. Now I’ll look at how we can speed things up.
The Megadrive/Genesis core has been plagued from the start with graphical issues that result from the SDRAM controller not responding quickly enough. Over the last few days I’ve finally put some time into understanding the SDRAM controller used by the project and spent some time improving its throughput.
I’ve just made available an updated version of the Sega Megadrive / Genesis core for the Turbo Chameleon 64. The only change is to the joystick handling – I’ve untangled the joystick directions and remapped the buttons slightly.
There’s still not a lot of point in using a traditional 1-button C64 joystick with this, but I’ve also fixed a bug in my previous attempt which prevented the CDTV infra-red controller from working. This does now work, and the buttons are mapped as follows:
Play / Pause => Megadrive Start
Volume Up => Megadrive A
A => Megadrive B
B => Megadrive C
I’ve mapped Volume UP to button A simply because it physically feels in the right place. The CDTV pad isn’t super-responsive, so trying to use for serious gameplay is an exercise in frustration, but it does work, and the controllers are readily available from AmigaKit.
The new core can be found here: fpgagen_chameleon_20180305.zip