XO1.75 A1 A2 Changes


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These are the changes planned for the XO-1.75 A2 prototype, from the A1 prototypes.


A1 Electrical Fixes

These changes fix problems in the A1 prototypes:

Power Sequence

  • PR89 <- 10K
  • PC55 <- DNP
  • PR66 <- 10K

SOC Reset

This adds a pullup to the SOC_RESET# line, needed due to a +1.8V input on the SOC driven by a +3.3V EC.

  • Add a 10K pullup to SOC_RESET#


A schottky diode was provided to isolate the +1.8V SPI Flash power from the rest of the motherboard, allowing incircuit programming. The voltage drop introduced by this diode (D6) was unacceptable.

  • Remove D6 (shorting it)

USB Power

This transfers control of the USB power from the SOC to the EC.

  • TP199 to PQ26.2 (long blue wire)
  • PR60 <- DNP (near PQ26 on the bottom side of the PCB)

USB Role

This sets the default mode of the OTG USB interface to "master".

  • Short USBID (TP39) to GND


This corrects a default pullup on the WLAN SDIO bus.

  • R251 <- DNP
  • R250 <- 10K


This cleans up the camera clock signal.

  • L20 <- 0 ohms
  • R94 <- 22 ohms


This corrects a missing pullup on the codec reset line.

  • R36 <- 10K (top side, underneath the codec)
  • switch pins on microphone plug

Fix DCON green wiring

  • GFDDAT0~6 pins on DCON need to be wired as with CL1B, with the DCON GFDDAT0 input connected to GND.

SD Power

  • Add a turn-off clamp to the SD power supplies ?
  • Give control of SD power to the EC, not the SOC.

A1 Layout Fixes

Camera Conn.

Move the camera connector back to the correct location

Debug Conn.

  • Eliminate the Marvell JTAG debug connector.
  • Replace the Quanta JTAG debug connector with one easier to mount in the field ?


The WLAN LED is misplaced on the top side of the board.

  • LED5 should be placed where LED4 is currently located, and vice versa.

Serial Connectors

  • Provide proper keep-outs for the serial connectors!

SPI Headers

  • Do not route signals through the pads of an SPI header
  • Provide at least two vias stapling each pad to the PCB

SPI Flash ROMs

  • Use appropriate device width

WLAN mounting holes

  • If possible, restore the mounting holes provided in CL1B for attaching a WLAN card to a stand-alone motherboard.

Planned Feature Changes

OFW ROM Size Increase

  • Increase the SPI Flash used by Open Firmware to 2MBytes (from the 1MByte used in A1).

Audio Codec

  • Change to ALC5631Q
  • Wire input circuit to route internal mic. through the audio input jack.
  • Add DC input mode
  • Add Jack Sense for the headphone jack.
  • Increase the size of R179 and R173 to 0805 (minimum), and increase the value (330 ? 470 ?) as well.

Tactile Feedback

It is still unclear what motherboard level changes are needed to support this feature.

We are providing a cutout in the motherboard giving room for a driver, and also a connector location on the motherboard.

Internal Storage

  • Change the internal microSD slot to a full-sized SD slot.
  • Add a jumper to indicate whether OFW should try to boot from internal SD or eMMC (both will use the same MMC controller, and it needs to be plumbed up appropriately when defining pin mappings).

Embedded Controller

  • Change to EC IO3731
  • Add connection between the 610 and the EC for reprogramming the EC via its EDI interface
  • Ensure isolation between the EC and the 610 on the EDI bus when the 610 is powered off
  • We eliminated the I2C bus provided between the EC and the 620 in the A1.

Restore Gamepad

  • Modify the game buttons from 4 buttons to 8 buttons.

Battery Charger

  • Change battery charger IC as the one used in XO-1/1.5 is being EOL'd. Modify the related circuit.

Security Processor Serial Conn.

  • Add a serial connector dedicated to use by the security processor (CForth).
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