Add first HW findings

hardware.md

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+# Game HAT hardware
+
+## ICs
+
+| Type        | Usage |
+| ----------- | ----- |
+| RTD2660H    | Main display controller, HDMI input, ADC for joystick |
+| SW6106      | Power control, battery charging, power state LEDs |
+| APA2068     | Audio amplifier |
+| 25D80    ?  | 1Mbit SPI Flash, RTD2660 firmware & config |
+| CS4334K     | I²S DAC |
+| unmarked SOIC8 | ? possibly Audio?, Power? near headphone jack and byttery switch |
+
+## IO Hardware
+
+- 6 Buttons, tactile, 12mm x 12mm x 3mm case, square stem 4mm high.
+  - Select, Start, A, B, X, Y
+  - Button cap diameter 11.5mm, 13mm brim.
+  - Total height button+cap: 12.4mm
+  - Pad layout: 5.5m +- 0.75mm x 14.5mm +- 1.25mm
+- 2 Buttons, right angle micro button, square stem
+- Analog joystick with middle button. Typical XBox/PS style.
+
+The buttons can be used directly with mk_arcade_joystick_rpi, available from RetroPie-Setup.
+Use this `/etc/modprobe.d/mk_arcade_joystick_rpi.conf` (note: no support for middle button yet, see below):
+
+```conf
+options mk_arcade_joystick_rpi map=5 gpio=5,6,13,19,21,4,26,12,23,20,16,18
+```
+
+## Other Knowledge
+
+- The RTD2660H is used to translate the joystick X/Y analog axis into four distinct L/R/U/D GPIOs to the Pi.
+  - Pin 50/51, A-ADC0/1 is used on the RTD2660H
+  - Joystick middle button is connected to Pi Pin 5 (IO 03) vs Gnd (active low).
+- Power is broken when switching between battery and USB
+
+## Display
+
+Seems to be 3:2, 480x320 native. Setting this via HDMI in raspbian is difficult.
+Default config proposed by WaveShare is 800x600@60
+
+### Display EDID
+
+```hex
+00 FF FF FF FF FF FF 00 4A 8B 54 4C 01 00 00 00
+0C 11 01 03 81 46 27 78 8A A5 8E A6 54 4A 9C 26
+12 45 46 AF CF 00 95 00 95 0F 95 19 01 01 01 01
+01 01 01 01 01 01 01 1D 00 72 51 D0 1E 20 6E 28
+55 00 B9 88 21 00 00 1E 8C 0A D0 8A 20 E0 2D 10
+10 3E 96 00 B9 88 21 00 00 18 00 00 00 FD 00 32
+4B 18 3C 0B 00 0A 20 20 20 20 20 20 00 00 00 FC
+00 33 32 56 33 48 2D 48 36 41 0A 20 20 20 01 29
+02 03 21 71 4E 06 07 02 03 15 96 11 12 13 04 14
+05 1F 90 23 09 07 07 83 01 00 00 65 03 0C 00 10
+00 8C 0A D0 90 20 40 31 20 0C 40 55 00 B9 88 21
+00 00 18 01 1D 80 18 71 1C 16 20 58 2C 25 00 B9
+88 21 00 00 9E 01 1D 80 D0 72 1C 16 20 10 2C 25
+80 B9 88 21 00 00 9E 01 1D 00 BC 52 D0 1E 20 B8
+28 55 40 B9 88 21 00 00 1E 02 3A 80 D0 72 38 2D
+40 10 2C 45 80 B9 88 21 00 00 1E 00 00 00 00 D0
+```