GSP Shared Memory

This page describes the structure of the GSP shared memory. Interrupt, framebuffer, and GX command data is stored here.

Interrupt Queue

The Interrupt queue is located at sharedMemBase + (clientID * 0x40).

Index Byte	Description
0x0	Offset from the count where to save incoming interrupts
0x1	Count (max 0x20 for PDC, 0x34 for others)
0x2	Missed other interrupts (set to 1 when 0 and count >= 0x34)
0x3	Flags (bit0 = skip PDC)
0x4-0x7	Missed PDC0 (incremented when flags.bit0 is clear and count >= 0x20)
0x8-0xB	Missed PDC1 (same as above)
0xC-0x3F	Interrupt list (u8) (0=PSC0, 1=PSC1, 2=PDC0/VBlankTop, 3=PDC1/VBlankBottom, 4=PPF, 5=P3D, 6=DMA)

GSP fills the interrupt list, then triggers the event set with RegisterInterruptRelayQueue for the specified process(es).

PDC interrupts are sent to all processes; other interrupts are only sent to the process with GPU rights.

Framebuffer Info

The framebuffer info structure for the top LCD is located at sharedMemBase + 0x200 + (clientID * 0x80).

The framebuffer info structure for the bottom LCD is located at sharedMemBase + 0x240 + (clientID * 0x80).

Framebuffer Info Header

Index Byte	Description
0	Framebuffer info entry index
1	Flags (bit0 = client has set new data)
3-2	Padding

Framebuffer Info Structure

Index Word	Description
0	Active framebuffer (0 = first, 1 = second)
1	Left framebuffer VA
2	Right framebuffer VA (top screen only)
3	Stride (offset 0x90)
4	Format
5	Status (offset 0x78)
6	? ("Attribute")

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 Queue

The command queue is located at sharedMemBase + 0x800 + (clientID * 0x200). It consists of an header followed by at most 15 command entries. Each command entry is of size 0x20 and has an header followed by command specific parameters.

After adding a command, TriggerCmdReqQueue must be used to trigger GSP processing when the total commands field is value 1.

Command Queue Header

Index Byte	Description
0	Index of the command to process, this is incremented by GSP before handling the command
1	Total commands to process, this is incremented by the application when adding the command to the queue, and decremented by GSP before handling the command
2	Flags (bit0 = completed?, bit7 = fatal error)
3	? (bit0 = set flags.bit0)
4	Result code for the last GX command which failed

Command Header

Index Byte	Description
0	Command ID
1	?
2	? (bit0 = set queue.flags.bit0 after processing)
3	When set, the command fails if GSP is busy handling any other command; otherwise, it only fails if GSP is busy handling a command of the same kind

Commands

Addresses specified in parameters are virtual addresses. For applications these are normally located in GSP memory, while for other processes they are located in VRAM.

Address and size parameters except for command 0 and command 5 must be 8-byte aligned.

Trigger DMA Request

Index Word	Description
0	u8 CommandID is 0x00
1	Source address
2	Destination address
3	Size
6-4	Unused
7	Flush source (0 = don't flush, 1 = flush)

This command is normally used to DMA data from the application GSP heap to VRAM. When flushing is enabled and the source buffer is not located within VRAM, svcFlushProcessDataCache is used to flush the source buffer.

Trigger Command List Processing

Index Word	Description
0	u8 CommandID is 0x01
1	Buffer address
2	Buffer size
3	Update gas additive blend results (0 = don't update, 1 = update)
6-4	Unused
7	Flush buffer (0 = don't flush, 1 = flush)

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. When flushing is enabled, svcFlushProcessDataCache is used to flush the buffer.

Trigger Memory Fill

Index Word	Description
0	u8 CommandID is 0x02
1	Buf0 start address (0 = don't fill anything)
2	Buf0 value
3	Buf0 end address
4	Buf1 start address (0 = don't fill anything)
5	Buf1 value
6	Buf1 end address
7	Control0 | (Control1 << 16)

This command 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.

The values of Control0 and Control1 give information about the type of memory fill. See here for more information about memory fill parameters.

Trigger Display Transfer

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.

The GPU color buffer is stored in the same Z-curve (tiled) format as textures. By default, SetDisplayTransfer converts the given buffer from the tiled format to a linear format adapted to the LCD framebuffers.

Display transfers are performed asynchronously, so after requesting a display transfer you should wait for the PPF interrupt to fire before reading the output data.

Some color formats seem to require specific input / output sizes when performing a display transfer, doing an RGB5A1->RGBA4 display transfer would never fire the PPF interrupt with a 32x32 buffer, increasing the buffer to 128x128 made it fire correctly.

Trigger Texture Copy

Index Word	Description
0	u8 CommandID is 0x04
1	Input buffer address.
2	Output buffer address.
3	Total bytes to copy, not including gaps.
4	Bits 0-15: Size of input line, in bytes. Bits 16-31: Gap between input lines, in bytes.
5	Same as 4, but for the output.
6	Flags, corresponding to the Transfer Engine flags. However, for TextureCopy commands, bit 3 is always set, bit 2 is set if any output dimension is smaller than the input, and other bits are always 0.
7	Unused

This command is similar to cmd3. It also triggers the GPU Transfer Engine, but setting the TextureCopy parameters.

Flush Cache Regions

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.