Playstation GPU reversing [56k Warning]

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Akari
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Playstation GPU reversing [56k Warning]

Post by Akari » July 26th, 2016, 6:22 am

Meanwhile we receive pictures of decapped GPU (without delayering yet).

Old 160 pin GPU and RGB converter
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Also here is working material - new GPU of revision Q and CQ. Looks alike. Only difference is inner revision with additional Y in the end. Looks like all difference will be in cell login. Does anyone know what was changed in different GPU revisions?

Image

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nocash
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Re: Playstation GPU reversing [56k Warning]

Post by nocash » July 28th, 2016, 2:21 am

Wow, more chips decapped, and delayering is also planned? I am wondering if the GPU circuit will be simplier than the CPU/MDEC/DMA stuff! There aren't too many (known) GPU differences, here are some notes from psx-spx:
GPU Versions
Most or all PSX games seem to detect and support at least two slightly different GPU versions. The games are using GP1(10h) with index 7 to obtain the GPU version number, the standard version seems to be 00000002h, used in PSone's and reportedly also in PSX consoles. Not sure if/which consoles do actually have different version numbers... maybe <very> old PSX'es... or maybe the program code is only a relict for compatibility with even older early prototypes?
The differences between the versions seem to apply mainly to the Texture Disable feature, and to how many bits of the Texpage attribute are reflected to which bits of GPUSTAT.
The standard GPU version (version=2) seems to use GP1(09h)=1 to disable textures. For non-standard GPUs (version<>2), the games seem to additional check whether Texpage.Bit12 can be written to GPUSTAT.Bit12, by setting "GP0(E1h)=GPUSTAT AND 3FFFh OR 2000h", and do then eventually use GP1(20h)=504h to disable textures, or GP1(20h)=501h to enable them.
Although the games do contain program code for texture disable, that feature seems to be mainly intended for debugging purposes, and most or all released games do never actually execute that code.
Note: The Textured Rectangle X/Y-Flip feature is said to be not working on very old GPU versions.
Then here's a recent thread about visible rendering differences, viewtopic.php?f=47&t=1035

And, pinouts for the 160pin GPU chip, viewtopic.php?f=70&t=1027 - that chip used dual-ported VRAM (with two databusses), so the GPU's memory interface should be quite different as in later chips... and will probably also cause different rendering timings.

Hmmmm, and if the "rectangles" in the decapped GPU photos are memory/cache blocks... that looks fairly different in old/new chips... maybe there are more huge differences (?) or maybe it's just some simplified design, still maintaining nearly identical behaviour as in older hardware.

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