Differences

This shows you the differences between two versions of the page.

--- lcd_controller [2025/03/22 02:27] – arisotura
+++ lcd_controller [2025/05/17 00:05] (current) – arisotura
@@ Line 1: / Line 1: @@
 ====== LCD controller ======
-The gamepad provides simple framebuffer-based display hardware.
+The gamepad provides simple display hardware that can display a video feed (from the camera or the H264 decoder) and a framebuffer overlay on top.
 Register map:
@@ Line 13: / Line 13: @@
 | 0xF0009418 | Horizontal end of display |
 | 0xF000941C | Vertical end of display |
-| 0xF0009420 | ?? |
+| 0xF0009420 | Video feed X offset |
-| 0xF0009424 | ?? |
+| 0xF0009424 | Video feed width |
-| 0xF0009428 | ?? |
+| 0xF0009428 | Video feed Y offset |
+| 0xF000942C | Video feed height |
+| 0xF0009430 | ?? |
+| 0xF0009434 | ?? |
 | 0xF0009460 | Framebuffer X offset |
 | 0xF0009464 | Framebuffer width |
@@ Line 22: / Line 25: @@
 | 0xF0009470 | Framebuffer stride |
 | 0xF0009474 | Framebuffer address |
+| 0xF0009478 | ?? |
 | 0xF0009480 | Display control |
+| 0xF0009484 | ?? |
+| 0xF0009488 | ?? |
+| 0xF0009490 | ?? |
+| 0xF0009494 | ?? |
 | 0xF00094B0 | Pixel format |
 | 0xF00094B4 | ?? |
+| 0xF00094B8 | ?? |
+| 0xF00094BC | ?? |
+| 0xF00094C0 | ?? |
+| 0xF00094C4 | ?? |
 | 0xF00094C8 | VCount - current vertical position |
+| 0xF00094D0+(N*4) | YUV->RGB matrix (N=0..8) |
+| 0xF00094F4 | ?? |
+| 0xF00094F8 | Camera sync |
 | 0xF00094FC | Counter of sorts |
+| ||
 | 0xF0009500 | Palette address |
 | 0xF0009504 | Palette data |
@@ Line 33: / Line 49: @@
 | 0xF0009510 | VCount IRQ position 3 |
 | 0xF0009514 | VCount IRQ position 4 |
-| 0xF0009600+(N*4) | Color correction LUT entry N |
+| ||
+| 0xF0009600+(N*4) | Color correction LUT entry N (N=0..31) |
 | 0xF0009684 | Color correction mask |
+| ||
 | 0xF0009700 | ?? |
 | 0xF0009704 | ?? |
@@ Line 137: / Line 155: @@
 ^ Bits ^ Desc. ^
 | 0    | ?? breaks display |
-| 1    | Must be set for display to work. Presumably enables overlay. |
+| 1    | Enable display (0=black screen) |
-| 2    | ?? causes weird effects |
+| 2    | Enable video feed (camera/H264?) |
-| 3    | ?? |
+| 3    | Video feed input? (0=post-processed camera?, 1=raw camera?) |
-| 4    | Must be set for display to work. Presumably general display enable. |
+| 4    | Enable overlay |
+| 5    | ?? |
+| 6    | ?? |
 **0xF00094B0**
@@ Line 150: / Line 170: @@
 | 2    | ?? |
 | 3    | ?? |
-| 7    | Weird color mode (YUV?) |
+| 7    | Color mode; 0=RGB, 1=YUV |
 | 8    | ?? collapses overlay to 1px vertical line |
 | 9    | ?? |
@@ Line 164: / Line 184: @@
 For the paletted formats, see the palette registers.
+Bit 7 causes color components to be interpreted as YUV, with the following mapping: R=V, G=Y, B=U. It seems the handling is different based on the pixel format? Notably, in YUV mode, pixel formats 0 and 1 seem to entirely ignore the palette and instead somehow directly convert indices to color components.
+In YUV mode, the matrix at 0xF00094D0..0xF00094F0 is used to convert the YUV components to RGB.
@@ Line 169: / Line 193: @@
 Current vertical position.
+**0xF00094D0+(N*4)**
+YUV->RGB matrix.
+^ Register   ^ Description   ^ Default value |
+| 0xF00094D0 | Y -> G factor | 0x0A5 = 74 |
+| 0xF00094D4 | U -> G factor | 0x04E = -14 |
+| 0xF00094D8 | V -> G factor | 0x062 = -34 |
+| 0xF00094DC | Y -> B factor | 0x0A5 = 74 |
+| 0xF00094E0 | U -> B factor | 0x122 = 136 |
+| 0xF00094E4 | V -> B factor | 0x000 = 0 |
+| 0xF00094E8 | Y -> R factor | 0x0A5 = 74 |
+| 0xF00094EC | U -> R factor | 0x000 = 0 |
+| 0xF00094F0 | V -> R factor | 0x0B9 = 114 |
+The factors work in a bit of a weird way.
+^ Bits ^ Desc. ^
+| 0-5  | Amount |
+| 6    | Sign |
+| 7-8  | Multiplier; 0=1, 1=2, 2/3=4 |
+The sign bit makes the value negative, but it's not two's complement. Instead: 0x3F = 63, 0x7F = -63.
+The multiplier allows to increase the final value. For example, values 0x30, 0x98, 0x10C and 0x18C are equivalent.
+Note: YUV mode produces darker colors, even with maximum factor values. One can use the color correction registers at 0xF0009600 to compensate for this.
+**0xF00094F8**
+Camera sync.
+^ Bits ^ Desc. ^
+| 0-10 | Vertical position |
+| 15   | ??? |
+This register allows to synchronize camera output to the display. The camera frame IRQ fires 8 scanlines after the specified position.
+This register can be disabled by setting it to a value equal to or greater than the display's total vertical span (as set in 0xF0009404). In this case, the camera outputs at its 'natural' framerate without synchronizing to the display, and the camera frame IRQ fires whenever a frame is finished.