Trusted
225
edits
Changes
Clarity bit6 alternative mode, clean up interlacing language, elaborate how fb interlacing works, and minor cleanup on the text below the fb format register table
|-
|-
| 5-4
| 5-4
| Framebuffer scanline output mode (framebuffer interleave config)
| Framebuffer interlacing mode
0 - A (output image as normal)
0 - A (no interlacing)
1 - AA (output a single line twice, so framebuffer A is interleaved with itself)
1 - AA (scanline doubling)
2 - AB (interleave framebuffer A and framebuffer B)
2 - AB (interlace enable)
3 - BA (same as above, but the line from framebuffer B is outputted first)
3 - BA (same as above, but the fields are inverted)
In AB and BA interlace modes, a scanline from each framebuffer is output in an alternating manner. In AB mode, Framebuffer A is output on the frist display scanline. Similarly, in BA mode, Framebuffer B gets output to the first display scanline.
The way AB and BA modes work, is that a scanline is output, the framebuffer stride value is added to the internal scanline pointer value, and the other framebuffer is selected. And this alternates until the end of the draw region.
AA interlacing works like AB interlacing, except both internal framebuffer pointers are set to the Framebuffer A pointer value.
In A mode (no interlacing), it doesn't switch to the other framebuffer at the end of outpuitting a scanline to the display.
Bottom screen has this set to 0 (A mode, no interlacing) at all times.
Top screen uses AB interlacing in 3D mode (with 3D slider enabled), and A mode (no interlacing) in 2D mode.
|-
|-
| 6
| 6
| Scan doubling enable?* (used by top screen)
| Alternative pixel output mode*
|-
|-
| 7
| 7
| DMA size
| DMA size
0 - 4 words (32 bytes)
0 - 4 FCRAM words (32 bytes)
1 - 8 words (64 bytes)
1 - 8 FCRAM words (64 bytes)
2 - 16 words (128 bytes)
2 - 16 FCRAM words (128 bytes)
3 - ???
3 - ???
|}
|}
* The weird thing about scan doubling, is that it works different between the bottom and top LCD. On the bottom LCD, it doubles the number of outputted pixels (so the same pixel is outputted twice, effectively doing column doubling). However on the top screen, it does scanline doubling instead. Considering that the bottom screen's table doesn't work on the top screen, this could give a hint as to how the top screen receives the pixel data from the PDC.
<nowiki>*</nowiki> The weird thing about bit6, is that it works different between the bottom and top LCD. On the bottom LCD, it doubles the number of outputted pixels (so the same pixel is outputted twice, effectively doing pixel/column doubling). However on the top screen, it does scanline doubling instead.
Most likely the top screen receives two pixels at once per clock unit, outputting two scanlines simultaneously.
On a 2DS, it seems to have no effect on the top part of the display, and on the bottom screen it just shifts the framebuffer to the right two pixels.
On a 2DS, it seems to have no effect on the top part of the display, and on the bottom screen it just shifts the framebuffer to the right two pixels.
GSP module only allows the LCD stereoscopy (3D) 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.
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.
When both interlacing and scan doubling are disabled, the full resolution of the top screen (240x800) can be utilized if the PDC registers are updated to accomodate this higher resolution. GSP contains tables for this mode (gsp mode == 1). GSP automatically applies this mode if both bit5 and bit6 are cleared. This is also the default, and the only valid mode for the bottom screen in userland.
When both interlacing and alternative mode is disabled (bit6=0), the full resolution of the top screen (240x800) can be utilized if the PDC registers are updated to accomodate this higher resolution. GSP contains tables for this mode (gsp mode == 1). GSP automatically applies this mode if both bit5 and bit6 are cleared. This is also the default, and the only valid mode for the bottom screen in userland.
If only AB interlacing is enabled, gsp detects this as a request to switch to 3D mode (gsp mode == 2), and enables the parallax barrier.
If only AB interlacing is enabled (bit5=1, bit6=0), gsp detects this as a request to switch to 3D mode (gsp mode == 2), and enables the parallax barrier.
It's unknown how to control this, but some other PDC registers control if interlacing should be done by true interleaving (both framebuffers are treated as 240x400), or skipping lines (both framebuffers are treated as 240x800)
It's unknown how to control this, but some other PDC registers control if interlacing should be done by true interleaving (both framebuffers are treated as 240x400), or by skipping lines (both framebuffers are treated as 240x800).
If only scan doubling is enabled, gsp detects it as a request to switch back to 2D mode for the top screen (gsp mode == 0). This is also the default mode for the top screen.
If only alternative mode is enabled (bit5=0, bit6=1), gsp detects it as a request to switch back to 2D mode for the top screen (gsp mode == 0). This is also the default mode for the top screen.
Both interlacing and scan doubling can't be enabled in usermode, but it works as expected in baremetal.
Both interlacing and scan doubling can't be enabled in usermode, but it works as expected in baremetal.