XO4 A2 B1 Changes

These are the changes planned for the XO-4 B1 prototype, from the A2 prototypes. The list of changes made to the A2 prototypes as part of testing is the XO-4 A2 ECO list.

A2 Electrical Fixes

These changes fix problems in the A2 prototypes:

Fixing +3.3V_SOC

This fixes a problem where +3.3V_SOC doesn't quite turn on.

• Change PR79 to a 10K resistor

Larger issue is that we used bipolar transistors in three places where we should have used MOSFETs. I propose changing PQ1, PQ34, and PQ42 to NMOS FETs and restoring PR40, PR79, and PR114 to 330K.

Fixing EC Programming by the SOC

This fixes the inability of the SOC to reprogram the EC.

• Add a 3K pullup resistor to +3.3V_NAND to EC_EDI_DO

New VCore

This changes to lower Vcore values for debugging and normal operation (1.3 and 1.24V), as well as a higher suspend voltage (1.0V) as suggested by Marvell for B0 silicon.

• PR62 (or PR57) should be 12.0K
• PR67 should be 18.0K
• PR66 should be 120K
• PR73 should be 30.0K

Pulse JTAG Reset at start of day

Marvell added a requirement to assert JTAG reset only at the start of day.

• Add a small schottky between EN_+1.35V_DDR3 and PRI_TRST#. The cathode of the diode should be connected to EN_+1.35V_DDR3.
• Remove the 100K resistor from R335.
• Populate R334 with a 100K resistor.

Changing to a +1.8V SPI Flash

Until we get the voltage translator working at SPI Flash speeds, we are disabling it and using a +1.8V 1 MByte SPI Flash ROM for U17.

• Depopulate R280 (0 ohm)
• Populate R281 with a 0 ohm resistor
• Populate R246 with a 120K resistor
• Replace U17 with a +1.8V SPI Flash
• Short Q27, pins 1 and 3
• Short Q28, pins 1 and 3
• Short Q29, pins 1 and 3
• Short D4, pins 1 and 2

Fixing SOC/EC Communications

This removes much of the voltage translation circuitry which was added to support an eventual change of masters in the EC/SOC SDI (SPI) bus. It fixes a reliability problem when talking to the EC.

• Remove the resistors from the following locations: R94 (3K), R98 (3K), R253 (3K), R258 (3K), R372 (1.2K), R373 (1.2K), and R375 (1.2K).
• Replace D18 with a 3K resistor.
• Remove Q38, and place a 3K resistor between pins 1 and 3
• Remove Q36, and place a 3K resistor between pins 1 and 3
• Add a 3K pullup resistor to +3.3VSUS_EC (or +3.3VSUS) to EC_SDI_MISO (Q37, pin 3).
• Add a 3.6K pulldown from SDI_MOSI (D18 anode) to GND
• Add a 3.6K pulldown from SDI_CLK (Q36.1) to GND
• Add a 3.6K pulldown from SDI_CS# (Q38.1) to GND

Simplify +1.2V Power

This eliminates an unnecessary power switch in the +1.2V rail (used mainly to bias some unused functional blocks in the SoC).

• Remove PQ38, PC104 and PR87
• Tie PQ38.2 to EN_NAND_SOCGPIO# and eliminate the EN_+1.2V signal from the EC.

Minor Fixes

Minor fixes suggested by Marvell upon schematic review:

• Pull VCXO_REQ low
• Pull JTAG_SEL high by default

IR PCB Connector

• Added series termination on TOUCH_SPI_CLK, TOUCH_SPI_SIMO
• Changed from 14 pin to 12 pin.

A2 Layout Fixes

IR PCB Connector

• Changed from 14 pin to 12 pin.
• Move CN5 over to avoid extra bends in FFC to IR PCB.

Planned Feature Changes

Add second serial port

Connect UART 1 up to a serial connector. As it is a +1.8V signal, add a level translator on the output signal and a voltage divider on the input. This can be depopulated for production.