Upgrading Clearfog Base to support CN9130 SOM

This guide is meant to explain how to upgrade the the ClearFog Base to support both CN9130 SOM and A388 SOM.

Removal of conflicting parts

Remove the components from table below:

#	RefDes	Qty	Action	Comments
1	R153	1	Remove	RES 740ohm
2	U24	1	Remove	74LVC1G125GW
3	U26	1	Remove	74LVC1G125GW

The components locations are marked green in the pictures below:

Components side

Print Side

Impact

The changes outlined partially impact functionality of the M.2 connector:

1. pin 6 (FULL_CARD_POWER_OFF#) is left floating

2. pin 67 (RESET#) is left floating

If an M.2 module is missing internal pull-ups, or has internal pull-down, it might permanently stay powered off or in reset.

As a workaround the IOs originally controlling the operational amplifiers U24 / U26 can be connected directly to M.2 connector using short wire, as shown below:

Workaround for floating M.2 control signals

FULL_CARD_POWER_OFF

Some LTE modules were found to have integrated pull-down for FULL_CARD_POWER_OFF, therefore the following workaround is recommended:

RESET

RESET is specified as a 1.8V signal for M.2, digital IO has 3.3V logic level. Therefore no workaround is recommended.

If strictly required, operation may be safe in open-drain configuration as long as software behaviour is validated first.

SFP Rate-Select (RS0/RS1)

Note: Clearfog Base revision 1.4.4 and later already include these changes.

Dis-/Assemble the components from table below:

#	RefDes	Action	Comments
1	R40, R41	Remove	resistor 0Ω
2	R37, R38	Add	resistor 1kΩ

The components locations are marked red in the picture below

cfbase_a38x_cn9130_sfp.png

Impact

R37/R38 enable high-speed mode (10Gbps) for TX and RX on SFP modules. Without this change CN9130 SoM SFP port will be limited to sgmii (2.5Gbps and lower) speeds even though the cpu side supports up to 10Gbps.

SoC Clocking Bootstrap

Note: Clearfog Base revision 1.4.8 and later already include these changes.

Dis-/Assemble the components from table below:

#	RefDes	Action	Comments
1	R153	Add	resistor 470Ω

The components locations are marked red in the picture below:

cfbase_a38x_cn9130_bootstrap.png

Impact

R153 pulls CP_MPP[15] high during reset, which makes possible (but does not activate by itself) 2.2GHz cpu speed.