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   Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:57 JST Foone🏳️‍⚧️

   So I'm working on implementing support for GameLink, which is an underdocumented protocol for talking to DOSBox, to let you grab frames and memory and submit input and such.

   So I'm gonna write out some of how it works just so I'll (hopefully) understand it

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:47 JST Foone🏳️‍⚧️

     in reply to

     enough debugging the game and the script to talk to dosbox to debug the game, let's debug dosbox! why not!

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:48 JST Foone🏳️‍⚧️

     in reply to

     or not. it seems to get the value 0x62 for every byte in memory. That's... weird.

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:48 JST Foone🏳️‍⚧️

     in reply to

     so GFX_EndUpdate calls OUTPUT_GAMELINK_Transfer.

     OUTPUT_GAMELINK_Transfer calls GameLink::Out, which should set the values I'm looking at, including version.

     GreenSkyOverMe (Monika) repeated this.
   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:49 JST Foone🏳️‍⚧️

     in reply to

     okay the version trick isn't working (and I'm not sure why), but this process is successfully getting bytes out.

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:50 JST Foone🏳️‍⚧️

     in reply to

     PermissionError: [WinError 5] Access is denied.

     WHAT

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:50 JST Foone🏳️‍⚧️

     in reply to

     okay that was just a thinko.

     but now I'm doing my version trick and it's not working. maybe I missed something

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:51 JST Foone🏳️‍⚧️

     in reply to

     MapViewOfFile(shm_handle, FILE_MAP_READ, 0, 0, 0)

     hey foone maybe if you want write access, you should ask for it

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:52 JST Foone🏳️‍⚧️

     in reply to

     I think (but I'm not 100% certain) that the addresses it wants are 32bit linear addresses. So if you're running at 16-bit DOS program (and who isn't?), you'll need to linearize your address

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:52 JST Foone🏳️‍⚧️

     in reply to

     well my first attempt at PEEKing over GameLink seems to be silently segfaulting python

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:53 JST Foone🏳️‍⚧️

     in reply to

     a dumb-but-should-work way:
     set the sSharedMemoryMap_R4.version to some other value. DOSBox-x sets it every frame (and never reads it, so it doesn't care what it is set to)

     So if you read the value and it's 4, you know DOSBox-X has processed all your peeks. If it's not 4 yet, sleep a bit then lock the mutex and check again

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:54 JST Foone🏳️‍⚧️

     in reply to

     So the way it works is that you set addr_count to how many bytes you want to read, and set the appropriate addresses in addr.
     then you release the mutex and wait

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:54 JST Foone🏳️‍⚧️

     in reply to

     dosbox will fill out the data values for the requested addresses.

     I'm not sure how you know dosbox has filled them out.

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:55 JST Foone🏳️‍⚧️

     in reply to

     So, the peek interface.
     https://github.com/joncampbell123/dosbox-x/blob/921acaa2915db5ea28b2ecba520a15e42e218175/src/gamelink/gamelink.h#L70C1-L77C4

     It's got addr_count, addr, data. The later two being arrays.

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     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:56 JST Foone🏳️‍⚧️

     in reply to

     Code to refer to is here:

     https://github.com/joncampbell123/dosbox-x/tree/master/src/gamelink

     So it's a shared memory region and a mutex. The way it works is you hold the mutex to access the shared memory.

   • Embed this notice
     Foone🏳️‍⚧️ (foone@digipres.club)'s status on Wednesday, 07-May-2025 15:06:56 JST Foone🏳️‍⚧️

     in reply to

     The top level struct is sSharedMemoryMap_R4.

     https://github.com/joncampbell123/dosbox-x/blob/921acaa2915db5ea28b2ecba520a15e42e218175/src/gamelink/gamelink.h#L108C9-L108C28