RAM values on power on?

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ge97aa
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RAM values on power on?

Post by ge97aa » Sun Sep 20, 2020 8:32 am

Does anyone know what values the RAM in a real SNES will hold when the power is turned on? Is it deterministic? Is it consistent across power-ons? Is it consistent across all SNES's? I'm trying to reverse-engineer some games that (no-doubt unintentionally) read data from memory before it's ever written, and would like to be able to determine what their behaviour would be on a real SNES. I currently use the bsnes-plus debugger to assist with this, but this emulator seems to populate RAM with random values on power-up, which I suspect is not authentic.

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Nikku4211
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Re: RAM values on power on?

Post by Nikku4211 » Sun Sep 20, 2020 9:50 am

It's random.
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dougeff
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Re: RAM values on power on?

Post by dougeff » Sun Sep 20, 2020 12:22 pm

But not reliably random that you could use initial RAM values as random numbers. It might be all zeroes. It might be all FF.

The emulators that fill RAM with random numbers is just as misleading as emulators that fill with zero.
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lidnariq
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Re: RAM values on power on?

Post by lidnariq » Sun Sep 20, 2020 12:40 pm

Almost all RAMs are mostly consistent, but have a few random bits on power up. Here's an article about using it: https://hackaday.com/2015/06/29/true-ra ... ue-hacker/

creaothceann
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Re: RAM values on power on?

Post by creaothceann » Sun Sep 20, 2020 1:51 pm

My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10

ge97aa
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Re: RAM values on power on?

Post by ge97aa » Mon Sep 21, 2020 5:14 am

Wow, fascinating topic. Thanks for all the links. So what it all boils down to is - not particularly random, but non-deterministic enough that it's pretty hard to make useful predictions. Fair enough.

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