GPU/External Registers

This page describes the address range used to configure the basic GPU functionality. Note that 3D rendering setup is not done via MMIO but instead by loading GPU command lists by writing to 0x1EF018F0.

Map

User VA	PA	Length	Name	Comments
0x1EF00004	0x10400004	4	?
0x1EF00010	0x10400010	16	Memory Fill1	GX command 2
0x1EF00020	0x10400020	16	Memory Fill2	GX command 2
0x1EF00030	0x10400030	4	?
0x1EF00400	0x10400400	0x100	Framebuffer Setup (top)
0x1EF00500	0x10400500	0x100	Framebuffer Setup (bottom)
0x1EF00C00	0x10400C00	?	Transfer Engine

Memory Fill

User VA	Description
0x1EF000X0	Buffer start physaddr >> 3
0x1EF000X4	Buffer end physaddr >> 3
0x1EF000X8	Fill value
0x1EF000XC	The low u16 for this register is overwritten by the GX command u16 parameter

These registers are used by GX command 2. 0x1EF00010 is used for the GX command buf0 parameters, while 0x1EF00020 is used for the GX command buf1 parameters.

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 size	Framebuffer width * pixel byte-size.
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	Set when the main screen 3D right framebuffer address is set.
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	Actual color components ordering
0	GL_RGBA8_OES
1	GL_RGB8_OES	BGR
2	GL_RGB565_OES	RGB
3	GL_RGB5_A1_OES
4	GL_RGBA4_OES

Framebuffers

The above framebuffer registers contains the physical address for each framebuffer, normally located in FCRAM in the application's GSP heap. When other processes use GSP as well, the framebuffers for the process is stored in VRAM instead.

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.

Transfer Engine

Register address	Description
0x1EF00C00	Input physical address>>3
0x1EF00C04	Output physical address>>3
0x1EF00C08	Output framebuffer dimensions, used with cmd3
0x1EF00C0C	Input framebuffer dimensions, used with cmd3
0x1EF00C10	Flags, used with cmd3 and cmd4.
0x1EF00C14	GSP module writes value 0 here prior to writing to 0x1EF00C18, for cmd3.
0x1EF00C18	Setting bit0 starts the DMA transfer.
0x1EF00C20	Unknown, used with cmd4
0x1EF00C24	Unknown, used with cmd4
0x1EF00C28	Unknown, used with cmd4

These registers are used by GX command 3 and 4. For cmd4, *0x1EF00C18 |= 1 is used instead of just writing value 1. The dimensions fields seem to use the same format as LCD register 0x1EF00X5C. The input framebuffer width for the main screen is normally 480.

0x1EF00C10

Bit	Description
0	When set, the framebuffer data is flipped vertically.(Normally zero)
1	When set, the framebuffer data is converted to tiles. (Normally zero)
2	This bit is set when the out-framebuf width/height is less than the input framebuf width/height, clear otherwise. Bit24 is normally clear when this bit is set.
3	When set, the framebuffer data is copied linearly, without doing any conversion (by default it is converted from tiles to linear). This has priority over bit1.
4	Unused
5	Unknown, normally zero.
7-6	Unused
10-8	Input framebuffer color format, value0 and value1 are the same as the LCD framebuffer formats.(Usually zero)
11	Unused
14-12	Output framebuffer color format
15	Unused
16	When this is set, the framebuffer data is converted to tiles.(Normally zero)
19-17	Unused
21-20	Unknown, output framebuffer data doesn't seem to change when this value is changed.(Normally zero)
23-22	Unused
24	This is set when the input_framebufwidth = output_framebufwidth<<1.
31-25	Unused

0x1EF018E0

Register address	Description
0x1EF018E0	Buffer Size>>3
0x1EF018E8	Buffer physical address>>3
0x1EF018F0	Writing value 1 here triggers GPU processing for the specified buffer

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

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