I would like to use the UARTs on beaglebone black or at least one of them. I found a big variety of information concerning this topic. Unfortunately many of it seems quite outdated.
the hardware is supported by the Kernel via device-tree and more specific functions by overlays
i found instructions to build own device trees
pins must be configured by config-pin?
Sometimes the resulting devices are called /dev/ttyOx, sometimes /dev/ttySx
i found information that dt overlays are managed by uboot instead of the kernel itself now
there is a library (adafruit) for using the uarts in python. But it has something to do with devicetrees too?
could it be that the ttyOx devices are related to the adafruit library?
Im using the am335x-debian-11.7-iot-armhf-2023-09-02-4gb.img.xz image.
What is the prefered way to use the uarts today?
My conclusion was that it should be enough to append
uboot_overlay_addr4=BB-UART2-00A0.dtbo
to /boot/uEnv.txt. Indeed i found the following message while booting:
uboot_overlays: loading /boot/dtbs/5.10.168-ti-r71/overlays/BB-UART2-00A0.dtbo ...
1017 bytes read in 4 ms (248 KiB/s)
So i expected to be able to use /dev/ttyS2.
But it isn’t.
Ok, i have done some investigation in the meantime.
First of all i have to apologize for bothering you: I’ve made an error in counting port pins :-).
But i will summarize my findings. Maybe somebody can confirm this though.
ttyOx is related to adafruit python library which is superfluous and need not to be used any more.
the kernel always initializes the uart hardware which is tied to ttySx device files. (/dev/ttySx can be opened even if not used by overlay or config-pin)
the “other side” of the uart hardware can be tied to io pins either with config-pin or uboot_overlay. (both is equivalent)
building own device trees is unnecessary
So the only thing that must be done to use the uarts is in uEnv.txt (example for uart2):