RDP Command: Set Texture Image big frame buffer address?

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RDP Command: Set Texture Image big frame buffer address?

Post by Narann » Thu Oct 29, 2015 12:09 am

When I parse this Display Command:

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   opcode fmt sz           width-1           DRAM addr
I get roughly this:

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Parser|Set Texture Image|Format: RGBA, Pixel Size: 16 bits, Width: 128, Texture Buffer Address: 8359192
What surprise me is the Frame Buffer address:

The last 26 bits: 00011111111000110100011000 are actually 8359192 (0x7F8D18).

It's almost a 8MB address. Of course, I know there is some memory table stuff involved and I'm sure this texture is clearly not in RDRAM (in the cartdrige?).

I naively followed the memory map and fall into the "unused" part of the RDRAM memory...

But I must admit I failed to understood how I could resolve this address.

I know there is some RSP segment table stuff but from what I see in this address, the segment is 0 meaning pure physical address (am I wrongly interpreting bits?).

I've looked at the SP registers but it's not quite clear.

EDIT: Wow! I've disabled Expansion Pack emulation in mupen64plus and the address is now: 4164888 (0x3F8D18) which fall into the RDRAM range 1 (2 MB).

Range 1 start address is: 0x00200000.

Actual address in Range 1 memory chip is 0x3F8D18 - 0x00200000 = 2067736


2 MB = 2*1024*1024 = 2097152

2097152 - 2067736 = 29416

So, the Set Texture Image seems to define a buffer at the 29416th Byte from the end of the RDRAM...

I'm very surprised a program could change addressing based on hardware modification (Expension Pack). It's very suspicious...

I'm using mupen64plus-rsp-cxd4 plugin for my test (which is supposed to be LLE). Is there any known n64 behaviour addressing textures from the end of the RDRAM?

PS: It's 1080 Snowboarding (There was no Expansion Pack involved during its release). For a unknown reason, the same RDP command sequences seems to be repeated at startup.

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Re: RDP Command: Set Texture Image big frame buffer address?

Post by MarathonMan » Sun Nov 01, 2015 4:06 pm

I am pretty sure the RDP wraps around addresses when it crosses 4/8MB boundary (depending on presence of expansion pack), but it's definitely something you should check.

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