Optimus Black serial¶

• Table of contents
• Optimus Black serial
  • Hardware setup
    • USB connector
      • FSUSB63 DP3T switch
      • MAX14526 MUIC
    • Logic level voltage
  • Software setup
    • Bootloader
    • Kernel
    • References

The Optimus Black allows accessing an UART serial port through the USB connector. A MAX14526 MUIC is in charge of switching between the USB and UART lines. The UART line can be muxed either to the main processor's debug UART (UART3), to the modem's UART or to the modem's USB lines via a FSUSB63 DP3T switch. The modem's UART line can also be switched directly to the main processor via an analog switch.

Thus, a working configuration to access the serial port through the USB connector is to route the USB connector to the UART line with the MAX14526 MUIC and to route the UART line to the main processor's debug UART (UART3) with the FSUSB63 DP3T switch.

Block diagram of the USB and UART connection, according to the Optimus Black (P970) service manual:

On the other hand, the main processor's debug UART (UART3) can be accessed directly on the board, via the pins of the debug connector or via the pins of the FSUSB63 DP3T switch.

Hardware setup¶

USB connector¶

According to the FSUSB63 DP3T switch datasheet and the Optimus Black (P970) service manual, UART Rx is routed to USB DM (D-) and UART Tx is routed to USB DP (D+).

Hence, the USB DM (D-) has to be connected to the UART adapter's Tx pin and the USB DP (D+) has to be connected to the UART adapter's Rx pin.
GND has to be made common between the USB connector and the UART adapter. There is no need to connect the USB connector's VBUS to a positive voltage.

Note that there is no automatic software switching (yet) with U-Boot, so make sure that the FSUSB63 DP3T switch is switched to the main processor's UART and that the MAX14526 MUIC is switched to UART before connecting the UART receiver to the USB connector.

FSUSB63 DP3T switch¶

The FSUSB63 DP3T switch can be switched to the main processor's UART by setting the OMAP_UART_SW GPIO (161) high and the IFX_UART_SW GPIO (162) low.

MAX14526 MUIC¶

The MAX14526 MUIC can be switched to UART by writing 0x09 to register 0x03 on device address 0x44 on I2C bus 1 (I2C2). It can be switched back to USB by writing 0x00 at the same address.

Logic level voltage¶

The main processor's debug UART is using a 1.8V logic level. Most UART adapters expect 3.3V, so a logic level shifter has to be used between the device and the adapter to convert between 1.8V and 3.3V.

Software setup¶

Bootloader¶

Some development versions of U-Boot allow switching the USB connector to UART by pressing the G key (on the side) at boot.

LG's downstream version of U-Boot, that ships with Android version prior to 4.0, should allow switching the USB connector to UART by placing a 56 kOhm resistor between the ID and GND pins of the connector and pressing the volume down key at boot. LG's downstream version of LK, that ships with Android 4.0, may behave the same. This feature was not tested at this time.

Kernel¶

References¶

• Optimus Black (P970) Service Manual and Schematics
• OMAP36xx Technical Reference Manual

These documents are the propriety of LG Electronics and Texas Instruments and are not hosted by the Replicant project.
However, some excerpts from these documents are provided, for the purpose of providing technical evidence of the facts that are mentioned in this page. We believe that this particular use of the copyrighted work is fair use.