Difference between revisions of "GPU/Pitfalls"
(Mostly based on findings by yuriks) |
m |
||
| (3 intermediate revisions by the same user not shown) | |||
| Line 7: | Line 7: | ||
=== Vertex attribute alignment === | === Vertex attribute alignment === | ||
| − | Vertex components which are defined through [[GPU/Internal_Registers#GPUREG_ATTRIBBUFFERi_CONFIG1|GPUREG_ATTRIBBUFFERi_CONFIG1]] will be aligned. | + | Vertex components which are defined through [[GPU/Internal_Registers#GPUREG_ATTRIBBUFFERi_CONFIG1|GPUREG_ATTRIBBUFFERi_CONFIG1]] will be accessed aligned by the GPU. |
* Vertex attributes will be aligned to their component element size. | * Vertex attributes will be aligned to their component element size. | ||
* Padding attributes (Component type > 11) will always aligned to 4 byte offets into the buffer. | * Padding attributes (Component type > 11) will always aligned to 4 byte offets into the buffer. | ||
| + | * The stride which is passed to the GPU should be passed unaligned. | ||
=== Vertex stride in GPUREG_ATTRIBBUFFERi_CONFIG2 === | === Vertex stride in GPUREG_ATTRIBBUFFERi_CONFIG2 === | ||
| Line 19: | Line 20: | ||
=== Output mapping in GPUREG_SH_OUTMAP_MASK === | === Output mapping in GPUREG_SH_OUTMAP_MASK === | ||
| − | The output | + | The output masking in [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_MASK|GPUREG_SH_OUTMAP_MASK]] influences how the registers starting at [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_Oi|GPUREG_SH_OUTMAP_Oi]] map to outputs in the shader. |
| + | |||
If an output is disabled in [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_MASK|GPUREG_SH_OUTMAP_MASK]] it means that no slot in the [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_Oi|GPUREG_SH_OUTMAP_Oi]] registers is consumed. | If an output is disabled in [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_MASK|GPUREG_SH_OUTMAP_MASK]] it means that no slot in the [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_Oi|GPUREG_SH_OUTMAP_Oi]] registers is consumed. | ||
[[GPU/Internal_Registers#GPUREG_SH_OUTMAP_TOTAL|GPUREG_SH_OUTMAP_TOTAL]] configures the number of used consecutive slots in the outmap. | [[GPU/Internal_Registers#GPUREG_SH_OUTMAP_TOTAL|GPUREG_SH_OUTMAP_TOTAL]] configures the number of used consecutive slots in the outmap. | ||
| Line 53: | Line 55: | ||
== Shaders == | == Shaders == | ||
| − | === | + | === Configued Output components must be written exactly once === |
Each configured output component has to be written exactly once or the PICA freezes. | Each configured output component has to be written exactly once or the PICA freezes. | ||
Latest revision as of 20:52, 14 March 2016
This page collects some oddities and pitfalls of the PICA GPU which is used in the 3DS.
Internal Registers[edit]
Vertex attribute alignment[edit]
Vertex components which are defined through GPUREG_ATTRIBBUFFERi_CONFIG1 will be accessed aligned by the GPU.
- Vertex attributes will be aligned to their component element size.
- Padding attributes (Component type > 11) will always aligned to 4 byte offets into the buffer.
- The stride which is passed to the GPU should be passed unaligned.
Vertex stride in GPUREG_ATTRIBBUFFERi_CONFIG2[edit]
The vertex stride set in GPUREG_ATTRIBBUFFERi_CONFIG2 must match the actual size of the vertex contained in the buffer or the PICA will freeze or it won't draw anything.
If you want to use a different stride you have to pad the data accordingly with padding attributes.
Output mapping in GPUREG_SH_OUTMAP_MASK[edit]
The output masking in GPUREG_SH_OUTMAP_MASK influences how the registers starting at GPUREG_SH_OUTMAP_Oi map to outputs in the shader.
If an output is disabled in GPUREG_SH_OUTMAP_MASK it means that no slot in the GPUREG_SH_OUTMAP_Oi registers is consumed. GPUREG_SH_OUTMAP_TOTAL configures the number of used consecutive slots in the outmap.
Example:
| Register | Value | Meaning |
|---|---|---|
| GPUREG_SH_OUTMAP_TOTAL | 0x00000002 | 2 outputs enabled |
| GPUREG_SH_OUTMAP_MASK | 0x00000011 | o0 enabled, o4 enabled |
| GPUREG_SH_OUTMAP_O0 | 0x03020100 | o0 = pos.xyzw |
| GPUREG_SH_OUTMAP_O1 | 0x0B0A0908 | o4 = color.rgba |
| GPUREG_SH_OUTMAP_O2 | ... | (unused) |
Shaders[edit]
Configued Output components must be written exactly once[edit]
Each configured output component has to be written exactly once or the PICA freezes.
MOVA instructions can't be adjacent[edit]
Having 2 consecutive MOVA instructions will freeze the PICA. This can be relaxed by placing a NOP between 2 MOVAs or by rearranging the code.