XO1.75 A2 A3 Changes

These are the changes planned for the XO-1.75 A3 prototype, from the A2 prototypes.

A2 Electrical Fixes

These changes fix problems in the A2 prototypes:

SD power

These correct a mistake in Embedded Controller pin assignments for the SD power control signals.

• Depopulate R335 and R345.
• Remove Q16, and short pins 2 and 3 (marked I and O).
• Remove Q21, and short pins 2 and 3 (marked I and O).

VMEM stability

This corrects an undercompensation of the +1.5V memory power supply, and also delays the turn-on of the memory termination power supply.

• Change PR49 to 22K.
• Change PR52 to 47K.
• Populate PC37 with 0.1 uF.

eMMC

• Populate R95 with 10K.
• Connect BOOT_DEV_SEL to CN21.10
• Use +3.3V_SD1 to power the eMMC instead of +3.3V_NAND

J2

The MISO and MOSI pins on J2 are swapped (the SOC GPIO map was wrong).

• SPI_MISO should be connected to U10.2, J2.1, and U11.AD15 (GPIO43)
• SPI_MOSI should be connected to U10.5 , J2.4, and U11.AE15 (GPIO44)

A2 Layout Fixes

• Bring GPIO04 (pin 5) to a user-probeable pad, for brick recovery purposes. (It may need to be grounded during EC flash reprogram.)