Re: [stella] [MARIA] I got a 7800 question...please don't flame me :)

Subject: Re: [stella] [MARIA] I got a 7800 question...please don't flame me :)
From: "Eric Ball" <ericball@xxxxxxxxxxxx>
Date: Tue, 22 Jul 2003 17:52:05 -0400
From: "Dennis Debro" <ddebro@xxxxxxxxxxxxx>
> I was looking through the 7800 documentation and I see no mention of the
stack. Where is it? $100 - $13F is documented as being a shadow of page 0
(TIA and MARIA) and $140 - $1FF seems to be used by the 6116 (RAM chip).
Does the 7800 have a full page for the stack?

A good question.  The 7800 RAM memory map is full of weird shadows, but the
following is all that is needed:

1800-203F    2K + 64 bytes
2040-20FF    192 bytes    0040-00FF ZP shadow
2100-213F    64 bytes
2140-21FF    192 bytes    0140-01FF SP shadow
2200-27FF    1.5K

So there is 4K total, but two chunks are also used for zero page and stack
memory.  (Unlike the 2600, the two don't share RAM on the 7800.)

It should be noted that the 6532 RIOT RAM is mapped to 0480-04FF but should
not be used in 7800 mode.  The 6502 runs 50% faster in 7800 mode, and MARIA
has to slow it down for TIA and RIOT register accesses.

> Also how do you check for collisions? Do you use the same methods used
with the 2600?

Yep, the same methods.  Ohh, you mean the TIA collision registers :-)  MARIA
doesn't have any collision registers, so your game has to track sprite
positions and handle and collisions manually.  (The sprite list concept used
by the 7800 doesn't lend itself to simple collision flags anyway.)

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