6.5 Power and Backlight Control with ATtiny Atmel MCU

The ATtiny microcontroller in the Raspberry Pi Touch Display 2 manages power and backlight control. It interfaces via I2C through the REG_POWERON and REG_PWM registers. These registers are configured using the Raspberry Pi v2 panel regulator Linux driver.

Refer to github.com/raspberrypi/linux/blob/rpi-6.6.y/drivers/regulator/rpi-panel-v2-regulator.c.

A screenshot of a computer program AI-generated content may be incorrect.
  1. DISP_STATE_SET_BRIGHTNESS:
    • Is executed after DISP_STATE_CONFIG_MIPI_HOST (display initialization).
    • Writes to REG_PWM (0x03) with a fixed value of 0x9f using DISP_WriteRegister: 
      DISP_WriteRegister(REG_PWM, 0x9f, DISP_CLIENT_ID_MCU);
    • This configuration turns on the display backlight.
  2. DISP_STATE_POWER_ON:
    • Sends REG_POWERON (0x02, value 0x3) to activate the ATtiny, enabling backlight functionality:
      DISP_WriteRegister(REG_POWERON, 0x3, DISP_CLIENT_ID_MCU);
    • Ensures the ATtiny is powered before brightness control.