Getting Started With Gravitar Hardware Programming

[VGAGuy]

I am trying to write a new game for Atari's Gravitar hardware. I want to start with a simple message on the screen using the normal vector ROM, then later move on to making my own.
Any programming tricks for this? Also how does Trackball movement work, in games like Quantum for example? I know the very basics of 6502 assembly(LDA, STA, CMP, JMP, BNE, BEQ JSR and RTS).
Eventually, I would like to get a custom object moving on the screen, controlled by a trackball.

Any help is appreciated.

 

[Hurray Banana]

Look at some of Neil's (mitchellgant) posts, he's detailed quite a bit of the hardware during is multigame development

http://www.ukvac.com/forum/topic349983.html

 

[VGAGuy]

A lot of my information was found on that post.
He tried to send me his MAME ROM assembler but the attachment got messed up and never made it.
My main problem is that I can't find solid information on the AVG opcodes for Gravitar, it's either Star Wars or Major Havoc. Also getting 10 bit numbers to work will be interesting(maybe I should write a compiler later on).
Also how would one disassemble the vector rom? I need to find the memory location of the letters.

 

[Hurray Banana]

You need to look through the code in the debugger and find the routines that draw the text. You'll then be able to identify addresses for character definitions and the like.

Take a look at the mame source for the driver, to help witih the memory maps.

https://github.com/mamedev/mame/blob/0f0d39ef81562c75e79176dd3bebb1e491ca39d5/src/mame/drivers/bwidow.cpp

 

[Mitchell Gant]

A lot of my information was found on that post.
He tried to send me his MAME ROM assembler but the attachment got messed up and never made it.
My main problem is that I can't find solid information on the AVG opcodes for Gravitar, it's either Star Wars or Major Havoc. Also getting 10 bit numbers to work will be interesting(maybe I should write a compiler later on).
Also how would one disassemble the vector rom? I need to find the memory location of the letters.

If you can PM me an email address that allows sending a zip attachment with some simple text files in it, you can have my code to look at.

Atari don't use 10 bit numbers internally, it would be too slow for the poor 6502 to process for every object/vector. It's all done as 8 bit and shifted before object position draws.

If you look at http://www.wardclan.f9.co.uk there's an AVG disassembler, but it's a bit flaky, I'm no C++ Windows programmer! It will help find the relevant parts of the vector ROM for sure.

 

[VGAGuy]

I was looking for an AVG assembler, thanks for letting me know that one exists.
You can send to file to the email address I sent earlier, just rename the file extension to something random.

VGAGuy2017-08-08 00:50:14