docs: Add notes for porting a new board

README.md

@@ -9,6 +9,7 @@ laptops.
 - [Flashing firmware](./doc/flashing.md)
 - [Debugging](./doc/debugging.md)
 - [Creating a custom keyboard layout](./doc/keyboard-layout-customization.md)
+- [Adding a new board](./doc/adding-a-new-board.md)
 
 ## Dependencies
 

doc/adding-a-new-board.md

@@ -0,0 +1,83 @@
+# Adding a new board
+
+## Charger parameters
+
+- `CHARGER_CHARGE_CURRENT`: Currently the same for all boards (1536).
+- `CHARGER_CHARGE_VOLTAGE`: On the battery, look for 充电限制电压 (charge limit
+  voltage). Convert this from volts to millivolts.
+- `CHARGER_INPUT_CURRENT`: On the charger, look for DC output. Convert the
+  current from amps to milliamps.
+
+#### Example
+
+The gaze15 battery has
+
+```
+充电限制电压: 16.8Vdc
+```
+
+and its charger has
+
+```
+DC OUTPUT (输出/輸出): 19.5V⎓9.23A 180W
+```
+
+This gives
+
+```
+CFLAGS+=\
+	-DCHARGER_CHARGE_CURRENT=1536 \
+	-DCHARGER_CHARGE_VOLTAGE=16800 \
+	-DCHARGER_INPUT_CURRENT=9230
+```
+
+## GPIOs
+
+Use ecsim on the proprietary firmware to generate the configuration. Modify
+`src/main.rs` if the EC needs to be changed from 5570 to 8587. Refer to
+`gpio.sh`, which can automate the process.
+
+Use the EC page in the schematics to label everything.
+
+Not everything will be generated correctly, so check them manually when
+labeling. Examples include the M block not being included in the generated
+output, and `CCD_EN` being configured as `GPIO_IN` instead of `GPIO_OUT`.
+
+## Keyboard backlight
+
+Many models have backlit or RGB keyboards. The EC page in the board schematics
+should be sufficient to determine the method used to control the backlight.
+
+### DAC
+
+One of the DACs is be used for controlling the backlight level.
+
+Examples:
+
+- galp4
+- lemp9
+
+These models use `KBLIGHT_ADJ` to control the backlight level.
+
+### PWM
+
+One PWM line is used for controlling brightness, and three others are used for
+setting the red, green, and blue colors.
+
+Examples:
+
+- addw2
+- gaze15
+- oryp6
+
+These models use `EC_PWM_LEDKB_{R,G,B}` to control the color of the keys.
+
+### I2C
+
+I2C is used to communicate with the MCU that controls the keyboard backlight
+and color.
+
+Examples:
+
+- darp6
+- oryp5