Stupid hypothetical question…has anyone tried installing a 65816 in a 7800?

[Lynxpro]

As stated in the topic title, I figure this is a stupid hypothetical question to ask whether anyone has actually tried installing a 65816 into a 7800?

 

The reason for my pondering is due to the fact that there are a few videos on YouTube showing the results of games played on various Atari 8-bit computers after installing a 65816 in the place of the original 6502C [sALLY] CPU.

 

Now I assumed this wouldn't work because of how the MARIA graphics chip famously halts the SALLY often to draw its graphics and that might cause a lock-up with a 65816 but then I just read that Atari's SALLY was designed to be halted and the A8's ANTIC graphics chip did that long before the debut of the MARIA yet the A8'ers that have posted to YouTube claim 95% - or better - compatibility with their software libraries after the 65816 mod. If I recall correctly, back in the Apple //gs days, Apple themselves only claimed about 90% compatibility with the existing Apple // software library with the 65816. And Nintendo didn't seem to be interested in trying to preserve NES [6502 ish] compatibility with the 65816 powered SNES.

 

If it worked on a 7800, I'd imagine the performance increase would be greater than the jump some games experience on the Sega Genesis after installing a 68010 in the place of the stock 68000 [which is better than over clocking but you no longer can play Shaq-Fu afterward, I know, the horror!].

 

Just thought I'd ask...

 

[Rybags]

Some of the computer '816 turbo upgrades also change the RAM for modern Static RAM and run the whole show at a faster speed, e.g. 7.2 or 14.4 MHz.

 

There's not a whole lot to gain by running a 6502 derivative at stock speed other than the extra instructions offered and they won't help existing software at all because it only uses stock 6502 instructions.

 

Although the 7800 RAM can be accessed at higher speed than the computer's stock 1.79 MHz, Maria tends to take quite a few of those cycles for graphics DMA.

But a turbo'd CPU on the 7800 would benefit in the offscreen area since Maria accesses are much less frequent or non-existent.

 

Thanks to the Atari architecture with the Sally CPU and it's /Halt function though, extra logic is generally needed when using a different CPU. The Atari way of doing it's thing is somewhat different to the way most 6502 machines work (albeit IMO better) so plugging in a different CPU isn't so straightforward.

Also, ROM access tends to be limited in speed vs modern day SRam, so that has to be catered for as well. And access to the I/O chips which in the 7800s case is already subject to slowdown.

Edited December 14, 2013 by Rybags

[retromod]

today you design your hardware via FPGA, that means a $2 chip gets a firmware and some port connectors to emulate the retro hardware. An Atari 2600 and Coleco system was already done in such chip and it is not bigger than 2x2 inches (without port, connectors on PCB of course).

But what is the target market for a faster 7800? You need new software and I don't know if there is really a market for it. So it make sense to extend an Atari XE/XL for hobby purposes (but why not use a regular PC for that as it will be incompatible to the old system?) but not a game system as it rely on software.

 

Have a look to the XM extension. If you want to market it in europe you must follow the regulations, so expect you need a fairly high number of units sold or you must duplicate the price. You must also follow the local dump regulations and as the XM is deliverd in a housing you fall into that regulation requirement of course. Even if you import that device the seller must do it if not for private purpose (so it can't be someone order more units for others as this leads to a highly risc to be charged for a fee). If you import the device into the european community and it contains a pokey chip which is normally non RoHS compliant than the device will be stopped at the border. You will never see it again because it is against law to deliver non-RoHS compliant components on new PCB's. Remember the kickstarter watch project failing in europe due to missing regulation papers so it was stopped and people never seen their ordered watches.

[Stun Runner 87]

why would anyone want to play The god awful Atari 7800 sound effects in stereo? The sound effects are bad enough as it is? I'll bet most people turn the volume down and just play the radio or music while plaing atari... Lol

 

The only atari game that would be good with surround sound would probably be commando.

Edited January 9, 2014 by Stun Runner 87

[Lynxpro]

why would anyone want to play The god awful Atari 7800 sound effects in stereo? The sound effects are bad enough as it is? I'll bet most people turn the volume down and just play the radio or music while plaing atari... Lol

 

The only atari game that would be good with surround sound would probably be commando.

 

I'd imagine getting TIA to output in stereo would be the first step in getting a POKEY or Dual POKEYs to output in stereo on the 7800, that's why it's important.

 

Home brew and hacks are adding back the base level audio [POKEY] that the 7800 should've been equipped standard. Stereo POKEY, Dual POKEY, and the YM2151 are just icing on the cake. Same with anyone crazy enough to dig up the AMY and made a production run of it.

[retromod]

.

Edited January 10, 2014 by retromod

[retromod]

If you only output them 1:1 in stereo there is no improvement. That is correct. But the stereo surround mod does a little bit more so sound is really better as it changes the audio output and re-arrange the output channels. All people having one are satisfied with the result and some wrote you can not believe sound is from a vcs. Even with the XM extension the Atari 7800 is still mono (from technical fact of implementation via cartridge slot).

 

The dual pokey is not RoHS compliant so some kind of illegal these days. Ignoring this fact by hardware enthusiasts do not make it legal. If you implement a fpga based pokey then it is legal as a FPGA is RoHS compliant.

All the problems with these extra chips is the programming. I love old game titles and that's why I collect and play them. If you must re-program it to work with an extension then it is not worth from collector and gaming point of view.

And this is - in my opinion - the problem of the XM extension. Better approach is to deliver a standard cartridge with soundchip on it and as you already need modified games deliver it together. Adding a DAC or more powerful component playing MP3 from another memory on the cartridge is not a big task - my own developments in that direction does not cost more than $10 for the whole PCB including a MCU and 4MB memory, allowing any kind of digitized sound up to 44KB/s (as the Atari 7800 has not 2 channels and only feeding mono 22KB/s is fairly enough).

So if for example Donkey Kong send a command to the MCU playing title 10 within the memory you immediately hear the original arcade sound digitized from the arcade machine. No magic!

Edited January 10, 2014 by retromod