report battery levels of central and peripheral halves to host

[mhantsch]

ZMK manages to report both battery levels (central and peripheral) to the host. Despite the default of Windows, MacOS and Linux only reporting the central battery state, there are tools available to show the level of all batteries, f.x. https://github.com/kot149/zmk-battery-center:

The battery level of the peripheral is reported in another BLE gatt attribute similar to the central battery.

It would be great if the UHK 80 also reported the level of both its batteries to the host.

[benedekkupper]

The Bluetooth BAS (Battery Service) has been significantly extended with version 1.1; it's no longer only reporting the battery level, but can also report battery present or not, charging or not, etc. (Some of) these functionalities are also supported by zephyr, see subsys/zephyr/bluetooth/services/bas/Kconfig.bas and bas_bls.c.

Another part of the change is that multiple BAS services can be implemented in one GATT server. In this case there is a descriptor attached to the battery level characteristic, that gives information about the battery. Currently zephyr's built-in descriptor (see level_cpf in subsys/zephyr/bluetooth/services/bas/bas.c is calling the battery as "main", by a Bluetooth SIG assigned enumeration, which is accessible here. The useful values are at the end, there are enum values for left and right too (0x010E and 0x010F respectively). To have two battery statuses reported over BLE, we could patch zephyr to report right and copy-paste the bas.c contents for a left side Battery Service.

[mhantsch]

This is the script I use to get battery levels of ZMK keyboards. It will also report the central battery of the UHK80 (but not the peripheral):

#! /bin/bash
#
# Obtain battery status of ErgoTravel keyboard halves (left and right).
# The keyboard must be using zmk firmware compiled to report both batteries.

debug=0
kbdname=ErgoTravel
#kbdname=Eyelash
#kbdname=UHK

if [ "$1" != "" ]; then
  kbdname="$1"
fi

# Obtain address of ErgoTravel keyboard
btaddr=`bluetoothctl devices | awk -v kbdname="$kbdname" -v debug="$debug" '$0 ~ kbdname { if(!debug) { for(i=3; i<=NF; i++) s=s?s " " $i:$i; print $2,s >"/dev/stderr" } print $2 }'`
test $debug -gt 0 && echo "btaddr: $btaddr"
if [ "$btaddr" == "" ]; then echo "No $kbdname device found."; exit 1; fi

# Find battery reporting services/attribute
bluetoothctl gatt.list-attributes $btaddr | 
  awk '/bluez/ && /service/ { srv_descriptor=$1 } /Battery Level/ { print srv_descriptor }' |
  ( while read -r srv; do 
  	( echo "gatt.select-attribute $srv"; echo "gatt.read"; sleep 1 ) | bluetoothctl >/dev/null 2>&1
        bluetoothctl gatt.attribute-info $srv | 
awk -Wposix '
function decval(hexval) {
  return sprintf("%d", "0x" hexval);
}
readval==1 { val=$1; readval=0 }
/Service:/ { svc=$2 }
/Value:/ { readval=1; next }
/Flags: read/ { print svc,decval(val) "%","<" val ">" }
'
	done
  )
exit 0

Output looks like this:

D4:E9:14:79:7D:FD ErgoTravel
/org/bluez/hci0/dev_D4_E9_14_79_7D_FD/service0015 100% <64>
/org/bluez/hci0/dev_D4_E9_14_79_7D_FD/service0010 45% <2d>>