# OVERLAYS
1. copy the `*.dtbo`` files in the overlay directory into the boot partition
2. add two config files into the boot partion, let's call them `sensing.txt`
   and `dualeth.txt`
Contents:
`sensing.txt`
```
dtparam=i2c_arm=on
enable_uart=1

dtoverlay=ed-sdhost
dtoverlay=i2c-rtc,pcf8563

dtoverlay=spi1-1cs
dtparam=cs0_pin=18,cs0_spidev=disabled
dtoverlay=ed-mcp2515-spi1-can0
dtoverlay=uart2
dtoverlay=uart3
dtoverlay=uart4
dtoverlay=uart5
gpio=11=op,dl
[all]

[cm4]
otg_mode=1
```

`dualeth.txt`
```
dtparam=i2c_vc=on
dtoverlay=i2c-rtc,pcf85063a,i2c_csi_dsi

[all]

[cm4]
otg_mode=1
```

These config files activate some external devices, mainly the RTC, but I have
two different board which have use different RTCs. The `dualeth` seems to have
the same one as the official CM4 IO Board, the `sensing` one has a different
one. Then I'll just `include` the corresponding file in the `config.txt` after
flashing the image.

# DRIVERS
1. driver `i2c-brcmstb` (option `CONFIG_I2C_BRCMSTB`) is missing:
```
grep -r CONFIG_I2C_BRCMSTB
./build_dir/target-aarch64_cortex-a72_musl/linux-bcm27xx_bcm2711/linux-5.10.146/.config:# CONFIG_I2C_BRCMSTB is not set
./target/linux/bcm27xx/bcm2710/config-5.10:# CONFIG_I2C_BRCMSTB is not set
./target/linux/bcm27xx/bcm2711/config-5.10:# CONFIG_I2C_BRCMSTB is not set
./target/linux/bcm27xx/bcm2708/config-5.10:# CONFIG_I2C_BRCMSTB is not set
./target/linux/bcm27xx/bcm2709/config-5.10:# CONFIG_I2C_BRCMSTB is not set
```

This is needed for the RTC to work. On Raspberry OS it's inside the kernel and
this is actually making the RTC i2c available. On openwrt I can't see the I2C
interface, and I think it's because this driver is missing. I don't care if
it's inside the kernel or as amodule as long as it's on the image.