GPU/External Registers

This page describes the address range accessible from the ARM11, used to configure the basic GPU functionality. For information about the internal registers used for 3D rendering, see GPU/Internal Registers.

Map

User VA	PA	Length	Name	Comments
0x1EF00004	0x10400004	4	?
0x1EF00010	0x10400010	16	Memory Fill1 "PSC0"	GX command 2
0x1EF00020	0x10400020	16	Memory Fill2 "PSC1"	GX command 2
0x1EF00030	0x10400030	4	?
0x1EF00034	0x10400034	4	GPU Busy	Bit31 = cmd-list busy, bit27 = PSC0 busy, bit26 = PSC1 busy.
0x1EF00050	0x10400050	4	?	Writes 0x22221200 on GPU init.
0x1EF00054	0x10400054	4	?	Writes 0xFF2 on GPU init.
0x1EF00400	0x10400400	0x100	Framebuffer Setup "PDC0" (top screen)
0x1EF00500	0x10400500	0x100	Framebuffer Setup "PDC1" (bottom)
0x1EF00C00	0x10400C00	?	Transfer Engine "DMA"
0x1EF01000	0x10401000	0x4	?	Writes 0 on GPU init and before the Command List is used
0x1EF01080	0x10401080	0x4	?	Writes 0x12345678 on GPU init.
0x1EF010C0	0x104010C0	0x4	?	Writes 0xFFFFFFF0 on GPU init.
0x1EF010D0	0x104010D0	0x4	?	Writes 1 on GPU init.
0x1EF014??	0x104014??	0x14	"PPF" ?
0x1EF018E0	0x104018E0	0x14	Command List "P3D"

Memory Fill

User VA	Description
0x1EF000X0	Buffer start physaddr >> 3
0x1EF000X4	Buffer end physaddr >> 3
0x1EF000X8	Fill value
0x1EF000XC	Control. bit0: start/busy, bit1: finished, bit8-9: fill-width (0=16bit, 1=3=24bit, 2=32bit)

Memory fills are used to initialize buffers in memory with a given value, similar to memset. A memory fill is triggered by setting bit0 in the control register. Doing so aborts any running memory fills on that filling unit. Upon completion, the hardware unsets bit0 and sets bit1 and fires interrupt PSC0.

These registers are used by GX SetMemoryFill.

LCD Source Framebuffer Setup

Offset	Length	Name	Comments
0x5C	4	Framebuffer width & height	Lower 16 bits: width, upper 16 bits: height
0x68	4	Framebuffer A first address	For top screen, this is the left eye 3D framebuffer.
0x6C	4	Framebuffer A second address	For top screen, this is the left eye 3D framebuffer.
0x70	4	Framebuffer format	Bit0-15: framebuffer format, bit16-31: unknown
0x78	4	Framebuffer select	Bit0: which framebuffer to display, bit1-7: unknown
0x90	4	Framebuffer stride	Distance in bytes between the start of two framebuffer rows (must be a multiple of 8).
0x94	4	Framebuffer B first address	For top screen, this is the right eye 3D framebuffer. Unused for bottom screen.
0x98	4	Framebuffer B second address	For top screen, this is the right eye 3D framebuffer. Unused for bottom screen.

Framebuffer format

Bit	Description
2-0	Color format
3	?
4	Unused?
5	Enable parallax barrier (i.e. 3D).
6	1 = main screen, 0 = sub screen. However if bit5 is set, this bit is cleared.
7	?
9-8	Value 1 = unknown: get rid of rainbow strip on top of screen, 3 = unknown: black screen.
15-10	Unused?

GSP module only allows the LCD stereoscopy to be enabled when bit5=1 and bit6=0 here. When GSP module updates this register, GSP module will automatically disable the stereoscopy if those bits are not set for enabling stereoscopy.

Framebuffer color formats

Value	Description
0	GL_RGBA8_OES
1	GL_RGB8_OES
2	GL_RGB565_OES
3	GL_RGB5_A1_OES
4	GL_RGBA4_OES

Color components are laid out in reverse byte order, with the most significant bits used first (i.e. non-24-bit pixels are stored as a little-endian values). For instance, a raw data stream of two GL_RGB565_OES pixels looks like GGGBBBBB RRRRRGGG GGGBBBBB RRRRRGGG.

Transfer Engine

Register address	Description
0x1EF00C00	Input physical address >> 3
0x1EF00C04	Output physical address >> 3
0x1EF00C08	DisplayTransfer output width (bits 0-15) and height (bits 16-31).
0x1EF00C0C	DisplayTransfer input width and height.
0x1EF00C10	Transfer flags. (See below)
0x1EF00C14	GSP module writes value 0 here prior to writing to 0x1EF00C18, for cmd3.
0x1EF00C18	Setting bit0 starts the transfer. Upon completion, bit0 is unset and bit8 is set.
0x1EF00C20	TextureCopy total amount of data to copy, in bytes.
0x1EF00C24	TextureCopy input line width (bits 0-15) and gap (bits 16-31), in bytes.
0x1EF00C28	TextureCopy output line width and gap.

These registers are used by GX command 3 and 4. For cmd4, *0x1EF00C18 |= 1 is used instead of just writing value 1. The DisplayTransfer registers are only used if bit 3 of the flags is unset and ignored otherwise. The TextureCopy registers are likewise only used if bit 3 is set, and ignored otherwise.

Flags Register - 0x1EF00C10

Bit	Description
0	When set, the framebuffer data is flipped vertically.
1	When set, the input framebuffer is treated as linear and converted to tiled in the output, converts tiled->linear when unset.
2	This bit is required when the output width is less than the input width for the hardware to properly crop the lines, otherwise the output will be mis-aligned.
3	Uses a TextureCopy mode transfer. See below for details.
4	Not writable
5	Don't perform tiled-linear conversion. Incompatible with bit 1, so only tiled-tiled transfers can be done, not linear-linear.
7-6	Not writable
10-8	Input framebuffer color format, value0 and value1 are the same as the LCD Source Framebuffer Formats (usually zero)
11	Not writable
14-12	Output framebuffer color format
15	Not writable
16	Use some kind of 32x32 block swizzling mode, instead of the usual 8x8 one.
17-23	Not writable
24-25	Scale down the input image using a box filter. 0 = No downscale, 1 = 2x1 downscale. 2 = 2x2 downscale, 3 = invalid
31-26	Not writable

TextureCopy

When bit 3 of the control register is set, the hardware performs a TextureCopy-mode transfer. In this mode, all other bits of the control register (except for bit 2, which still needs to be set correctly) and the regular dimension registers are ignored, and no format conversions are done. Instead, it performs a raw data copy from the source to the destination, but with a configurable gap between lines. The total amount of bytes to copy is specified in the size register, and the hardware loops reading lines from the input and writing them to the output until this amount is copied. The "gap" specified in the input/output dimension register is the number of bytes to skip after each "width" bytes of the input/output, and is NOT counted towards the total size of the transfer.

By correctly calculating the input and output gap sizes it is possible to use this functionality to copy arbitrary sub-rectangles between differently-sized framebuffers or textures, which is one of its main uses over a regular no-conversion DisplayTransfer. When copying tiled textures/framebuffers it's important to remember that the contents of a tile are laid out sequentially in memory, and so this should be taken into account when calculating the transfer parameters.

Command List

Register address	Description
0x1EF018E0	Buffer size in bytes >> 3
0x1EF018E8	Buffer physical address >> 3
0x1EF018F0	Setting bit0 to 1 enables processing GPU command execution. Upon completion, bit0 seems to be reset to 0.

These 3 registers are used by GX command 1. This is used for GPU commands.

Framebuffers

These LCD framebuffers normally contain the last rendered frames from the GPU. The framebuffers are drawn from left-to-right, instead of top-to-bottom.(Thus the beginning of the framebuffer is drawn starting at the left side of the screen)

Both of the 3D screen left/right framebuffers are displayed regardless of the 3D slider's state, however when the 3D slider is set to "off" the 3D effect is disabled. Normally when the 3D slider's state is set to "off" the left/right framebuffer addresses are set to the same physical address. When the 3D effect is disabled and the left/right framebuffers are set to separate addresses, the LCD seems to alternate between displaying the left/right framebuffer each frame.

Init Values from nngxInitialize for Top Screen

0x1EF00400 = 0x1C2
0x1EF00404 = 0xD1
0x1EF00408 = 0x1C1
0x1EF0040C = 0x1C1
0x1EF00410 = 0
0x1EF00414 = 0xCF
0x1EF00418 = 0xD1
0x1EF0041C = 0x1C501C1
0x1EF00420 = 0x10000
0x1EF00424 = 0x19D
0x1EF00428 = 2
0x1EF0042C = 0x1C2
0x1EF00430 = 0x1C2
0x1EF00434 = 0x1C2
0x1EF00438 = 1
0x1EF0043C = 2
0x1EF00440 = 0x1960192
0x1EF00444 = 0
0x1EF00448 = 0
0x1EF0045C = 0x19000F0
0x1EF00460 = 0x1c100d1
0x1EF00464 = 0x1920002
0x1EF00470 = 0x80340
0x1EF0049C = 0

More Init Values from nngxInitialize for Top Screen

0x1EF00468 = 0x18300000, later changed by GSP module when updating state, framebuffer
0x1EF0046C = 0x18300000, later changed by GSP module when updating state, framebuffer
0x1EF00494 = 0x18300000
0x1EF00498 = 0x18300000
0x1EF00478 = 1, doesn't stay 1, read as 0
0x1EF00474 = 0x10501