2 out of 4 boards present a problem with internet (ethernet)

[longsleep]

Well testing internet speed is pretty pointless. You should have a 'known-to-be-fast' peer and use iperf2 or iperf3 for testing locally, ideally with a direct connection (no switch).

There are plenty of guides out there how to rebuild a device tree from source.

Try something like this (all as root):

Code:

sudo su -

# install dt compiler
apt-get install device-tree-compiler

# download source device tree for Pine64+ to /boot/pine64
wget https://github.com/longsleep/build-pine64-image/raw/master/blobs/pine64.dts -O /boot/pine64/sun50i-a64-pine64-plus.dts

# Switch directory to /boot/pine64 and edit using Vi
cd /boot/pine64
vi sun50i-a64-pine64-plus.dts
# make modifications now

# Compile modified device tree
dtc -O dtb -o pine64-plus-custom.dtb sun50i-a64-pine64-plus.dts

# Make U-Boot load modified device tree
echo "fdt_filename=pine64/pine64-plus-custom.dtb" >>/boot/uEnv.txt

reboot

Note that these instruction do only work for device tree values used by the Kernel (like the sunxi-gmac settings). Also these instructions are for Pine64+ only!

rx-delay seems to be ok as 0.
tx-delay is 3 by default in my builds. In Android i think it is 2. Try modifying tx-delay only and keep the value between 0 and 7. Valid range for rx-delay is 0-31.

Also note that the values for rx and tx-delay are to be given as hex (base 16).

I suggest you set a static IP address for eth0 before playing with this, as DHCP will fail for incompatible values and DHCP has a 5 minute timeout on boot.

Have fun