XO4 A2 ECOs

From OLPC

These are recommended engineering change orders (ECOs) to the A2 prototype of the XO-4 laptop. This is NOT a list of changes from A2 to B1, that is located elsewhere.

[edit] Fixing +3.3V_SOC

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

• Change PR79 to a 10K resistor

[edit] 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

[edit] Fix VCore

This corrects a problem with the BOM. If you have a board that prints the CForth banner on the serial port but then hangs, this is likely the issue.

• Swap PR66 and PR73. PR73 should be 10.7K and PR66 should be 64.9K

Superseded by the following ECO

[edit] 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

[edit] 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.

[edit] Fix MMP3 B0 errata 1.15

Errata numbered 1.15 in v040, and numbered 1.32 in v060.

• Replace R45 with a 10 ohm resistor (pref. 0603 or 0805)
• Place three diodes in series between +1.8V_SOC_AVDD_FE (the side of R45 closest to the SOC) and GND, with the cathode connected to GND. The base-emitter junctions of PMST3904 transistors (pin 2 to pin 1) is used instead of diodes due to availability.

[edit] 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

[edit] 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

[edit] Alternate

An alternate fix for this problem was done to most boards:

• Add a 3K pullup resistor to +3.3VSUS_EC (or +3.3VSUS) to EC_SDI_MISO (Q37, pin 3).
• Add a 68 pF capacitor between Q36 pin 1 and GND. One motherboard required a 100 pF for reliable EC communication.

[edit] Fix abnormal power-off

When the power adapter is disconnected from the wall, but left connected to the laptop, the laptop crashes. This is due to the battery charge transistor PQ58 being backwards.

• Remove PQ58, and reinstall rotated 180 degrees with pins 4 and 8 lifted.
• Run a wire from the trace going to PQ58 pin 4 (on motherboard) to pin 4 (on chip).