mc6809e

You're right -- if you restrict yourself to configurations where the whole of the system is a CPU attached to a simple frame buffer and a DAC. But that wasn't the only solution available in the 80's. The Amiga, for instance, had a special DMA controller that accelerated graphics, sound processing, scrolling, etc, and greatly reduced the burden on the CPU. An admittedly limited form of wavetable synthesis came almost for free on the Amiga.

I've used the piggyback method to upgrade two non-atari systems. The idea is to solder all but one pin on each chip to the chip below it. The one unsoldered pin on each chip is the row address strobe (RAS) and is bent up and wired to the unconnected RAS of the device controlling access to DRAM. That's going to be the MMU. It should only take a few minutes to locate the right pin on a schematic. I'm not sure how this will work on the ST, though. Make sure you've got at least 250ns DRAMs. I know Atari put slower 265ns DRAMs in early STs to save money, but I wouldn't trust slower DRAMs for this project. At 8Mhz, the shifter and 68000 need access to DRAM within 250ns. I'm guessing that Atari was able to get away with the slower DRAM by using the MMU to aggressively steal every available odd memory cycle for DRAM refresh. But with this project, a little extra resistance between pins or a little extra capacitance cause by extra solder might cause errors with slower DRAM. Good luck.

Not always true. Predator looks like it plays better on the ST than the Amiga, although the audio on the Amiga version is a lot better... I've come to terms with the Amiga after many years and having been an ST owner back in the day. The Amiga has Atari DNA through and through, it's just a brother from a different mother...granted, she was a street walker but I digress! I'll still welcome an Amiga in my home. Edit: If I end up with an Amiga, that Commodore logo is gonna get removed... Haha. Yeah, the Amiga really has Atari blood running through it. It was a Commodore machine in name only. Too bad the way things worked out. Personally, I wish both companies would've just agreed to merge the ST and Amiga platforms back in 1987 following their legal settlement. Then we would've had a pretty strong combined [third] platform that might still be going strong today... Possibly. Creating a plugin card for PCs might have worked. I knew all kinds of people that wanted 68000 based Unix like options for their PCs. Mainframe on a chip they used to call the 68000. And Amiga actually had a patent on their blitter. How long did it take to get graphics acceleration on PCs? I think the first PC cards with blitters (not just line draw) arrived in 1991 and were pretty expensive. I have a Core2Duo machine with decent graphics. Billions of operations per second. The damn thing still stutters when rendering. MPEG video playback shows tearing.

Not always true. Predator looks like it plays better on the ST than the Amiga, although the audio on the Amiga version is a lot better... I've come to terms with the Amiga after many years and having been an ST owner back in the day. The Amiga has Atari DNA through and through, it's just a brother from a different mother...granted, she was a street walker but I digress! I'll still welcome an Amiga in my home. Edit: If I end up with an Amiga, that Commodore logo is gonna get removed... Haha. Yeah, the Amiga really has Atari blood running through it. It was a Commodore machine in name only. Too bad the way things worked out.

And thanks god it has not. I will take any AY buzz over low res sampled rubbish any time. Amiga's audio hardware was the wrong thing at the wrong time. There is not enough memory in the whole Amiga system to get a reasonable quality in this kind of "audio". And building the whole audio system just on samples playback with such a small RAM... I see no sence in this. Shame. It wasn't as bad as all that. The samples could be waveform tables of length two bytes to 128K bytes. The values were output as a loop and at a rate determined by a frequency divider. A square wave could be stored in just two bytes, for example.