SNES SRAM Test ROM

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poorstudenthobbyist
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SNES SRAM Test ROM

Post by poorstudenthobbyist » Tue Jul 28, 2020 5:03 pm

I've seen a bunch of miscellaneous test ROMs for SNES, but I haven't seen many that test for how much SRAM is on-board. And by extension, one should be able to tell what mode the cartridge is designed to use, as RAM locations are different between the two.

Is there any kind of test ROM that does this that I may have missed?

Markfrizb
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Re: SNES SRAM Test ROM

Post by Markfrizb » Tue Jul 28, 2020 7:42 pm

Huh? To what end? You’re asking for a program that would test the pcb that it’s installed into? Testing itself? Not sure I follow what you are asking about.

lidnariq
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Re: SNES SRAM Test ROM

Post by lidnariq » Tue Jul 28, 2020 7:55 pm

I assume poorstudenthobbyist wants a self-test for a cart so that they can verify that the RAM is working correctly on an all-new-parts reproduction and appears to be the right size.

I kinda thought I might have written one before, but I can't find it, so I guess I haven't.

Markfrizb
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Re: SNES SRAM Test ROM

Post by Markfrizb » Tue Jul 28, 2020 8:28 pm

I guess what makes the most sense is to have some external device run a cart integrity test before something is actually mounted on the cart.

Myself086
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Re: SNES SRAM Test ROM

Post by Myself086 » Tue Jul 28, 2020 8:44 pm

Almost 2 years ago, I ran into a SRAM issue that had different effects on snes9x and SD2SNES. I'm using 16kb of SRAM on HiROM and the mirroring was different.

This is certainly something I could've used.

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poorstudenthobbyist
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Re: SNES SRAM Test ROM

Post by poorstudenthobbyist » Tue Jul 28, 2020 8:53 pm

Here's what I want to do with it:

I offer PCBs with parts pre-mounted, and I recently found some surface mount SRAM to try out. My plan is to be able to produce carts with everything already on the board, except the EPROM. I designed a programming board with a SNES cart connector on it so I can plug these PCBs in and program the CIC through a Pickit3.

On that programming board, I also have the cart edge pins so that it can be placed into a SNES as well. This would also put the PCB in the cart connector in parallel with whatever I put on the programming board. I plan to have the test ROM on an EPROM that would be housed on the programming board, but use all the other circuitry on the PCB that I just prepared the CIC on. That way, I can verify that all the parts on the cart work, and importantly can tell me if the SRAM is detected or not.

The mode thing is just kind of extra, the main thing I want to check is the SRAM and if it's connected to the board correctly. I've never run into a problem with any of the PCBs from the board house, and no one has ever complained about them not working, but I always wanted to try to figure out a way to test them before I sold them (without soldering anything on them, obviously), just to make sure they work.

If such a thing doesn't exist, I suppose now might be as good a time as any to learn how to code SNES ROMs.

tepples
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Re: SNES SRAM Test ROM

Post by tepples » Wed Jul 29, 2020 2:45 am

It sounds almost exactly like why Paul at Infinite NES Lives commissioned me to make Holy Mapperel for testing assembly of his NES boards.

Markfrizb
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Re: SNES SRAM Test ROM

Post by Markfrizb » Wed Jul 29, 2020 6:00 am

poorstudenthobbyist wrote:
Tue Jul 28, 2020 8:53 pm
Here's what I want to do with it:

I offer PCBs with parts pre-mounted, and I recently found some surface mount SRAM to try out. My plan is to be able to produce carts with everything already on the board, except the EPROM. I designed a programming board with a SNES cart connector on it so I can plug these PCBs in and program the CIC through a Pickit3.

On that programming board, I also have the cart edge pins so that it can be placed into a SNES as well. This would also put the PCB in the cart connector in parallel with whatever I put on the programming board. I plan to have the test ROM on an EPROM that would be housed on the programming board, but use all the other circuitry on the PCB that I just prepared the CIC on. That way, I can verify that all the parts on the cart work, and importantly can tell me if the SRAM is detected or not.

The mode thing is just kind of extra, the main thing I want to check is the SRAM and if it's connected to the board correctly. I've never run into a problem with any of the PCBs from the board house, and no one has ever complained about them not working, but I always wanted to try to figure out a way to test them before I sold them (without soldering anything on them, obviously), just to make sure they work.

If such a thing doesn't exist, I suppose now might be as good a time as any to learn how to code SNES ROMs.
Sounds like my pcb (RetroCircuits) and the journey we went on many years ago. :D
The issue we had was not only testing the sram and it's functionality, but you also need to determine if the multiplexers are working right, and if the decoders are also functioning as they should. You may have a good sram but because the decoder is bad, you don't know which it is.
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poorstudenthobbyist
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Re: SNES SRAM Test ROM

Post by poorstudenthobbyist » Wed Jul 29, 2020 6:15 am

Yeah, I was trying to think of ways to test that out as well. I'm still thinking it through. In the meantime I can at least still test the CIC just fine with the programming board.

It looks like you might be using multiplexers to switch between Hi and LoROM? Unless there are solder pads on the back. That's what my very first design was going to use, but I opted for a simpler board with solder pad connectors on the back to switch between the two modes. Always kicked around the idea of going back, that might make this test easier to do. I might revisit that.

Ice Man
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Re: SNES SRAM Test ROM

Post by Ice Man » Thu Jul 30, 2020 8:45 am

If you want to properly test SRAM on a repro cart or whatever I suggest sanni's Cartreader.
It can dump alot of carts as we as read and write new save files to the carts and detect the SRAM size from the game's header (or can be specified as well iirc).

https://github.com/sanni/cartreader

Can only recommend building that. Very useful tool.

With this I was able to find a few faulty RAMs that were supposed to work according to my two programmers (TL866II plus and TOP300).
But they did not. Sanni's reader was correct in that case since it writes 0x00 from start to end and 0xFF after to check if all writes/reads are successful.

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