For what? using the uarts? If you're using a recent image then you don't
have to mess with overlays at all. In the default configuration, you can
configure pin function at runtime using the "config-pin" utility, e.g. for
uart4:

config-pin P9.11 uart   # switch P9.11 to uart 4 rxd
config-pin P9.13 uart   # switch P9.13 to uart 4 txd


The specific prerequisites for being able to do this are:
1. /boot/uEnv.txt contains 'enable_uboot_overlays=1' and
'enable_uboot_cape_universal=1' (both of these are typically present)
2. No cape overlay is loaded (as a result of cape autodetection or by
setting one of the uboot_overlay-variables in /boot/uEnv.txt)
3. The bootloader is recent enough. This is automatic when running from
eMMC, but if you're booting from SD card then the presence of an old
bootloader on eMMC may cause problems. Reflashing eMMC fixes this problem,
or you can just wipe eMMC using 'sudo blkdiscard /dev/mmcblk1'.

But indeed, using overlays instead is also still supported, set via the
uboot_overlay_* variables in /boot/uEnv.txt. Do note that doing so
implicitly disables "cape-universal", which means the config-pin utility
won't work.

Matthijs

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