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With Pokey Chips in short supply should a lock on cart be used instead?

Lock on Game Genie Pokey Atari 7800 homebrew short supply

22 replies to this topic

#1 redsteakraw OFFLINE  

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Posted Wed Mar 6, 2019 9:33 AM

So Given that there are a limited supply of pokey chips and that they mostly have to be taken from existing carts.  There will be a time where they either get too cost prohibitive or push games like ballblazer to be rare.  Given that wouldn't it make more sense to cannibalize one an create a pokey lock on cart like a game genie / Sonic and Knuckles.  And carts that use the Pokey just lock on to the cart and gain the extra capabilities.  Then the homebrew games don't need to worry about sourcing pokeys and all the other troubles and people that want the pokey can just use that one cart to boost the sound quality.  What are your thoughts?  Is this a dumb idea, do you think it is technically infeasible? 


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#2 RevEng OFFLINE  

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Posted Wed Mar 6, 2019 9:50 AM

A very large lock-on cart with POKEY and other hardware is nearing completion.

#3 Dauber OFFLINE  

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Posted Wed Mar 6, 2019 9:56 AM

I'm just curious as to why developers seem to be married to the POKEY for enhanced sound when other chips can be used, as has been proven by the XM and Rikki & Vikki.



#4 RevEng OFFLINE  

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Posted Wed Mar 6, 2019 10:16 AM

I'm just curious as to why developers seem to be married to the POKEY for enhanced sound when other chips can be used, as has been proven by the XM and Rikki & Vikki.


POKEY has developer momentum on the platform... POKEY cart hardware has already been created, while another sound chip would require new cart hardware. POKEY is present in 7800 emulators, while another sound chip would need implementation. There's a ton of documentation for POKEY's features, from the mundane to the arcane.

One of the reasons I was excited about batari's HOKEY chip, was it would be technically possible to modify the firmware to use other sound synthesis techniques, while still using existing cart hardware. That's half the dev work taken care of right there.

With the XM, the FM based sound-chip is one of its more exciting features. I can't wait to have TIA, POKEY, and YM2151 to play around with.

#5 TheProgrammerIncarnate OFFLINE  

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Posted Wed Mar 13, 2019 9:57 PM

What do you guys think of the FPGA recreation of the POKEY? The code probably could use some improvement, but a modern FPGA could serve as a viable replacement.



#6 Trebor OFFLINE  

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Posted Thu Mar 14, 2019 5:00 AM

What do you guys think of the FPGA recreation of the POKEY? The code probably could use some improvement, but a modern FPGA could serve as a viable replacement.

 

The xc95288 mentioned at the end of the thread to fully replace the POKEY chip, list between $150-$175 each in bulk when purchase 100+.  Individually nearly $250 a piece.

 

It doesn't appear to be a practically solution, unfortunately.



#7 TailChao OFFLINE  

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Posted Thu Mar 14, 2019 8:49 AM

I highly recommend a microcontroller based solution.
 
Not just because it's what we used on Rikki & Vikki, but because of all these things :

  • Price and Availability
    The MB9BF524K we used cost around $5.00 each when ordered in the hundreds. While this is more than none, you're guaranteed to get the chips you're paying for and they'll actually work. Sourcing NOS parts is extremely problematic and I've run into more than enough fake sound chips to drop this for any sort large scale production. Even with the required support components (crystal, caps, etc) the cost is still decent.
  • Space
    Small surface mount packages are nice and leave more room for other cartridge denizens.
  • Flexibility
    You can do mostly whatever sort of sounds you like, within the limits whatever microcontroller you use. There's plenty of good choices from Microchip, Atmel, etc. and lots of examples available online for how to do software rendered audio.
  • Speed
    Being able to offload sections of your audio driver to the microcontroller is a very nice perk, now Sally has more time to do game-related work.
     

Of course, it's up to the developer to decide what is most important for their game. But I think having to write the necessary support software is a small price for all the benefits above.



#8 RevEng OFFLINE  

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Posted Thu Mar 14, 2019 11:31 AM

I agree in general, but the software bit isn't the biggest hurdle for me. I've updated 7800 emulators and programed microcontrollers with sound engines before.

I just don't have hobby time or background to learn board design, nor the hobby cash to invest in tools, boards, and components.

Then there are those that will criticize for using non-period chips. We've already heard grumbling about the ym2151 inclusion in XM.

#9 TheProgrammerIncarnate OFFLINE  

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Posted Thu Mar 14, 2019 3:31 PM

 

The xc95288 mentioned at the end of the thread to fully replace the POKEY chip, list between $150-$175 each in bulk when purchase 100+.  Individually nearly $250 a piece.

 

It doesn't appear to be a practically solution, unfortunately.

 

Hmm, the xc95288 is a larger part, and also obsolete. I'm fairly confident that an entire 1-core POKEY could fit on a iCE40LP8K with room to spare, those cost a mere 7$ (less in bulk.) I think POKEY uses capacitor-timing polling (all digital) instead of an ADC and the DAC could be emulated by high-speed PWM. So all you would need would be the FPGA, the EEPROM, and some voltage converters plus the PCB to make a pin-compatible replacement. It wouldn't be dirt cheap, but it might be less expensive than the shrinking supply of real POKEYs. For emulation accuracy the circuit description could be extracted from the decapped images.



#10 TailChao OFFLINE  

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Posted Fri Mar 15, 2019 9:19 AM

I just don't have hobby time or background to learn board design, nor the hobby cash to invest in tools, boards, and components.

That's totally fair. But...

 

Then there are those that will criticize for using non-period chips. We've already heard grumbling about the ym2151 inclusion in XM.

...this argument is completely ridiculous, especially considering the YM2151 was used in Atari's System 1 the same year the 7800 was supposed to be released.



#11 RevEng OFFLINE  

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Posted Fri Mar 15, 2019 10:12 AM

...this argument is completely ridiculous, especially considering the YM2151 was used in Atari's System 1 the same year the 7800 was supposed to be released.


Yeah, completely agreed. I won't let it ruin my fun either.

#12 AtariLeaf OFFLINE  

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Posted Sat Mar 16, 2019 4:54 AM

What do you guys think of the FPGA recreation of the POKEY? The code probably could use some improvement, but a modern FPGA could serve as a viable replacement.

Not to change the subject but I think we're in need of FPGA recreations of chips like the TIA and perhaps other custom chips for Atari systems too.



#13 DrVenkman OFFLINE  

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Posted Sat Mar 16, 2019 5:06 AM

Not to change the subject but I think we're in need of FPGA recreations of chips like the TIA and perhaps other custom chips for Atari systems too.

 

Yeah. TIA chips have gotten CRAZY expensive from Best in the last year or so. I guess Bradley is getting down to his last boxes of a few items. This reminds me - I need to buy up a bunch of 2600 systems cheap this summer for donor parts. Still the most cost-effective way to keep systems running if you're capable of disassembling stuff and testing it.



#14 AtariLeaf OFFLINE  

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Posted Sat Mar 16, 2019 6:14 AM

$26 each and limit of 1. I agree, cheaper to buy systems at this point. The same concern was happening in the coco community with the GIME chip but I heard that is being worked on, if not close IIRC



#15 high voltage OFFLINE  

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Posted Sat Mar 16, 2019 12:11 PM

Which Atari 7800 cart releases use Pokey?



#16 AtariLeaf OFFLINE  

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Posted Sat Mar 16, 2019 12:43 PM

Which Atari 7800 cart releases use Pokey?


https://atariage.com...duct_list&c=109

#17 Jinks OFFLINE  

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Posted Sat Mar 16, 2019 12:52 PM

Which Atari 7800 cart releases use Pokey?

Only 2 commando and bblazer.

#18 AtariLeaf OFFLINE  

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Posted Sat Mar 16, 2019 1:23 PM

Oh I thought he was asking which homebrews use them

#19 high voltage OFFLINE  

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Posted Sat Mar 16, 2019 2:11 PM

Only 2 commando and bblazer.

 

Wow, just two, wasn't really worth it.



#20 high voltage OFFLINE  

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Posted Sat Mar 16, 2019 2:12 PM

 

Well, that's better, good to see them in homebrews



#21 TheProgrammerIncarnate OFFLINE  

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Posted Sat Mar 16, 2019 2:31 PM

 

Not to change the subject but I think we're in need of FPGA recreations of chips like the TIA and perhaps other custom chips for Atari systems too.

 

Cool, I'm working on old chip -> FPGA conversion. Do you have a list of ones that could use replacements (other than the POKEY, TIA, GTIA, CTIA, and FREDDIE)?



#22 DrVenkman OFFLINE  

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Posted Sat Mar 16, 2019 3:05 PM

 

Cool, I'm working on old chip -> FPGA conversion. Do you have a list of ones that could use replacements (other than the POKEY, TIA, GTIA, CTIA, and FREDDIE)?

 

ANTIC and SALLY

 

Note that FPGA implementations of the A8 chipset all already exist in the community (not sure about CTIA but GTIA does). The MiST project has an entire A8 computer implemented in a single FPGA. And there was an ABBUC hardware contest winner this past year called POKEYMAX that implemented single and stereo POKEY in a DIP40 configuration, though it has a small PCB that's got a larger-than-the-chip size package. 



#23 john_q_atari OFFLINE  

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Posted Sat Mar 16, 2019 10:48 PM

 

Yeah. TIA chips have gotten CRAZY expensive from Best in the last year or so. I guess Bradley is getting down to his last boxes of a few items. This reminds me - I need to buy up a bunch of 2600 systems cheap this summer for donor parts. Still the most cost-effective way to keep systems running if you're capable of disassembling stuff and testing it.

 

I bought multiple TSU branded TIA chips last year off of ebay for under $13 each and they all worked. I see the same seller I bought from still lists them for that same price on a regular basis. Unless you must have NOS, or a lot of chips in a short amount of time, the atari 2600 chips still seem to be relatively easy to obtain.

 

-Jeremiah


Edited by john_q_atari, Sat Mar 16, 2019 10:50 PM.






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