Excitebike saving/loading

Discuss emulation of the Nintendo Entertainment System and Famicom.

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oRBIT2002
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Excitebike saving/loading

Post by oRBIT2002 » Sun Mar 31, 2013 12:42 pm

I was annoyed, even since the 80's that I was not able to save my tracks on "Excitebike". Obviously the cartridge doesn't have SRAM and that explains that, but I've read somewhere that Excitebike was designed to work with some other kind of additional hardware (some kind of taperecorder a'la C64?) for saving/loading of tracks.
Would be interesting to know the facts concerning this matter. Anyone knows and actually tried it?
I've done some quick debugging and the game is obviously messing around with $4016 during saving. I can't recall I've ever seen an emulator support Excitebike-saves...(?)

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blargg
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Re: Excitebike saving/loading

Post by blargg » Sun Mar 31, 2013 12:55 pm

I'm guessing it uses some of the additional latched outputs on $4016 to generate the audio that's recorded to cassette.

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Movax12
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Re: Excitebike saving/loading

Post by Movax12 » Sun Mar 31, 2013 2:28 pm

I would guess the easiest way to get it working in an emulator (or with the powerpak) would be to add SRAM and intercept the $4016 writes.

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blargg
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Re: Excitebike saving/loading

Post by blargg » Sun Mar 31, 2013 2:53 pm

What would the SRAM store?

lidnariq
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Re: Excitebike saving/loading

Post by lidnariq » Sun Mar 31, 2013 3:11 pm

I remember some emulator actually supports the Family BASIC data recorder. I forget which.
Also:
http://wiki.nesdev.com/w/index.php/Fami ... a_Recorder
and
http://nesdev.com/tapedrv.PNG

zzo38
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Re: Excitebike saving/loading

Post by zzo38 » Sun Mar 31, 2013 3:29 pm

lidnariq wrote:I remember some emulator actually supports the Family BASIC data recorder. I forget which.
I think VirtuaNES does support it.
[url=gopher://zzo38computer.org/].[/url]

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Movax12
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Re: Excitebike saving/loading

Post by Movax12 » Sun Mar 31, 2013 4:03 pm

blargg wrote:What would the SRAM store?
I meant battery backed WRAM. Change the STA $4016 to JMP writeBitToRam

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blargg
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Re: Excitebike saving/loading

Post by blargg » Sun Mar 31, 2013 4:10 pm

There's going to be a lot of bits, given the encoding scheme. You'd also need a timebase since the delay between writes is critical (without that you'd likely just see 0 1 0 1 0 1).

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Movax12
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Re: Excitebike saving/loading

Post by Movax12 » Sun Mar 31, 2013 4:39 pm

The point was made here that intercepting the normal routine would only allow one save, and it would be better to write a new one with a menu for multiple saves. (And you would avoid all the tape protocol overhead.)

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Memblers
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Re: Excitebike saving/loading

Post by Memblers » Sun Mar 31, 2013 7:22 pm

Here is a mod to get the tape drive audio I/O on the NES, sent in by sepi.

edit: Just noticed lidnariq already linked to this, n/m. :)
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tapedrv.PNG

Drag
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Re: Excitebike saving/loading

Post by Drag » Sun Mar 31, 2013 11:37 pm

I remember poking around the load/save routines on Excitebike. If I recall correctly, the bits are encoded with frequency modulation. As in, a "1" bit is /¯\_/¯\_/, and a "0" bit is /¯¯¯\___/. (Or was it the other way around?)

So yes, it was indeed designed for a casette recorder, but we never got it in the US. :\

lidnariq
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Re: Excitebike saving/loading

Post by lidnariq » Mon Apr 01, 2013 12:08 am

I don't suppose you happen to recall where in the ROM the code is? For curiosities' sake, I'm trying to collect which games use what protocol and record it in the wiki.

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oRBIT2002
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Re: Excitebike saving/loading

Post by oRBIT2002 » Mon Apr 01, 2013 12:52 pm

The saving/loading of Excitebike is pretty much a mess (for my eyes anyway) and it's very hard to debug in FCEUX since it doesn't emulate a taperecorder. Anyway, I've managed to create an SRAM patch instead. Available on my website..

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blargg
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Re: Excitebike saving/loading

Post by blargg » Mon Apr 01, 2013 6:47 pm

Surely there's some routine that SAVE calls. So patch that out to just copy the entire NES RAM, and have LOAD just reverse that. No need to only save/load what the game does, unless some things should be preserved (high score maybe?).

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Re: Excitebike saving/loading

Post by ccovell » Mon Apr 01, 2013 10:54 pm

What I did during my investigations into Wrecking Crew & Castle Excellent was change the writes from $4016 to $4011 to record the saved signal as a WAV file in an emulator. Loading won't work, of course...

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