GSP Shared Memory

This page describes the structure of the GSP shared memory. GX commands and framebuffer info is stored here, and other unknown data.

Framebuffer info

The framebuffer info structure for the main LCD is located at sharedmemvadr + 0x200 + threadindex*0x80. The framebuffer info structure for the sub LCD is located at sharedmemvadr + 0x240 + threadindex*0x80.

Framebuffer info header

Index Byte	Description
0	Framebuffer info entry index
1	Flag
3-2	Padding

When a process sets this framebuffer info, it sets index to (index+1) & 1. Then it writes the framebuffer info entry, and sets flag to value 1. The GSP module loads this framebuffer info entry data into GSP state once the GPU finishes processing GX commands 3 or 4. Once the GSP module finishes loading this framebuffer info, it sets flag to value 0, then it will not load the framebuffer info again until flag is value 1. After loading this entry data into GSP state, the GSP module then writes this framebuffer state to the LCD registers. GSP module automatically updates the LCD framebuffer registers each time GX commands 3 or 4 finish, even when this shared memory data was not updated by the application.(GSP module toggles the active framebuffer register when automatically updating LCD registers, when shared memory data is not used)

The two 0x1C-byte framebuffer info entries are located at framebufferinfo+4.

3D Slider and 3D LED

See Configuration Memory.

Command Buffer Header

Index Byte	Description
0	Current command index. This index is updated by GSP module after loading the command data, right before the command is processed. When this index is updated by GSP module, the total commands field is decreased by one as well.
1	Total commands to process, must not be value 0 when GSP module handles commands. This must be <=15 when writing a command to shared memory. This is incremented by the application when writing a command to shared memory, after increasing this value TriggerCmdReqQueue is only used if this field is value 1.
2	Must not be value 1. When the error-code u32 is set, this u8 is set to value 0x80.
3	Bit0 must not be set
4	u32 Error code for the last GX command which failed

The command buffer is located at sharedmem + 0x800 + threadindex*0x200. After writing the command data to shared memory, TriggerCmdReqQueue must be used to trigger GSP processing for the command when the total commands field is value 1.

Command Header

Index Byte	Description
0	Command ID
2-1	?
3	When non-zero GSP module may check flags for the specified cmdID, command handling is aborted when the flags are set. The corresponding flag for each CmdID is set once the command is handled by GSP module, this flag is likely cleared once the GPU finishes processing the command.

The command is located at cmdbuf + 0x20 + cmdindex*0x20, the size of each command is 0x20-bytes. The command parameters are located at command+4. Addresses specified in parameters are application vaddrs, these are usually located in either the process GSP heap or VRAM. For applications these addresses are normally located in the GSP heap, while for other processes these addresses are located in VRAM. Addresses/sizes specified in parameters except for cmd0 and cmd5 must be 8-byte aligned.

Commands

GX RequestDma

Index Word	Description
0	u8 CommandID is 0x00
1	Source address
2	Destination address
3	Size
7-4	Unused

This command is normally used to DMA data from the application GSP heap to VRAM.

GX SetCommandList Last

Index Word	Description
0	u8 CommandID is 0x01
1	Buffer address
2	Buffer size
3	Flag, bit0 is written to GSP module state
6-4	Unused
7	When non-zero, call svcFlushProcessDataCache() with the specified buffer

This command converts the specified address to a physical address, then writes the physical address and size to the GPU registers at 0x1EF018E0. This buffer contains GPU commands.

GX SetMemoryFill

Index Word	Description
0	u8 CommandID is 0x02
1	Buf0 start address
2	Buf0 value
3	Buf0 end address
4	Buf1 start address
5	Buf1 value
6	Buf1 end address
7	The low u16 is width0, while the high u16 is width1 (?)

This commands converts the specified addresses to physical addresses, then writes these addresses and the specified parameters to the GPU registers at 0x1EF00010 and 0x1EF00020. Doing so fills the specified buffers with the associated 4-byte value. This is used to clear GPU framebuffers. The associated buffer address must not be <= to the main buffer address, thus the associated buffer address must not be zero as well. When the bufX address is zero, processing for the bufX parameters is skipped.

GX SetDisplayTransfer

Index Word	Description
0	u8 CommandID is 0x03
1	Input framebuffer address
2	Output framebuffer address
3	Input framebuffer dimensions
4	Output framebuffer dimensions
5	Flags, for applications this is 0x1001000 for the main screen, and 0x1000 for the sub screen.
7-6	Unused

This command converts the specified addresses to physical addresses, then writes these physical addresses and parameters to the GPU registers at 0x1EF00C00. This GPU command copies the already rendered framebuffer data from the input GPU framebuffer address to the specified output LCD framebuffer. The input framebuffer is normally located in VRAM. Note that unlike the LCD framebuffers, the GPU framebuffer seems to use fixed-point/floats for the color format.

GX SetTextureCopy

Index Word	Description
0	u8 CommandID is 0x04
1	Input buffer address
2	Output buffer address
3	Size
4	Input dimensions?
5	Output dimensions?
6	Flags, normally this is 0x8, with bit2 optionally set when either of the dimensions fields are set.
7	Unused

This command is similar to cmd3, this command also writes to the GPU registers at 0x1EF00C00.

GX SetCommandList First

Index Word	Description
0	u8 CommandID is 0x05
1	Buf0 address
2	Buf0 size
3	Buf1 address
4	Buf1 size
5	Buf2 address
6	Buf2 size
7	Unused

The application buffer addresses specified in the parameters are used with svcFlushProcessDataCache. The input buf0 size must not be zero. When buf1 size is zero, svcFlushProcessDataCache() for buf1 and buf2 are skipped. When buf2 size is zero, svcFlushProcessDataCache() for buf2 is skipped.