feat(ble): expose multiple battery services for split peripherals, with configurable user descriptions by kot149 · Pull Request #1038 · rmk-rs/rmk

kot149 · 2026-08-09T11:27:34Z

Summary

resolves #710

Expose battery levels from configured split peripherals through standard Battery Service instances on the central's BLE GATT server, including host-readable and notifiable levels for each peripheral.
Add configurable battery_user_description values for the central and split peripheral Battery Level characteristics through [ble], [split.central], and [[split.peripheral]], with descriptive defaults for each battery service.

Testing

Tested with a split keyboard (one split peripheral), using Microsoft Bluetooth LE Explorer and zmk-battery-center and verified:

the battery level can be read
the Characteristic User Description can be read
the bettery level update is notified

Only tested with a single peripheral. Configurations with two or more peripherals should also work but not tested.

Specification reference

This implementation follows the Bluetooth SIG Battery Service Specification v1.1, especially the requirements for multiple Battery Service instances and unique Characteristic Presentation Format Description values for each Battery Level characteristic:
https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/BAS_v1.1/out/en/index-en.html

github-actions · 2026-08-09T11:38:26Z

Size Report

Example	main	PR	Diff	.text	.data	.bss
`use_config/nrf52832_ble`	398.4 KiB	398.7 KiB	+0.07% ⬆️	+44	0	+272
`use_config/nrf52840_ble`	440.6 KiB	440.8 KiB	+0.03% ⬆️	-108	0	+272
`use_config/nrf52840_ble_split (central)`	502.5 KiB	506.3 KiB	+0.75% ⬆️	+2816	0	+1080
`use_config/nrf52840_ble_split (peripheral)`	317.5 KiB	317.5 KiB	-0.01% ⬇️	-68	+8	0
`use_config/pi_pico_w_ble`	673.3 KiB	673.9 KiB	+0.09% ⬆️	+356	0	+272
`use_config/rp2040`	146.1 KiB	146.1 KiB	+0.00%	0	0	0
`use_config/rp2040_split (central)`	159.7 KiB	159.7 KiB	+0.00% ⬆️	+4	0	0
`use_config/rp2040_split (peripheral)`	27.9 KiB	27.9 KiB	+0.00%	0	0	0
`use_config/stm32f1`	62.7 KiB	62.7 KiB	+0.00%	0	0	0
`use_config/stm32h7`	100.9 KiB	100.9 KiB	+0.00% ⬆️	+4	0	0
`use_rust/nrf52832_ble`	385.7 KiB	386.8 KiB	+0.26% ⬆️	+792	0	+272
`use_rust/nrf52840_ble`	436.1 KiB	436.2 KiB	+0.04% ⬆️	-72	0	+272
`use_rust/nrf52840_ble_split (central)`	505.8 KiB	508.4 KiB	+0.51% ⬆️	+2012	0	+680
`use_rust/nrf52840_ble_split (peripheral)`	315.3 KiB	315.2 KiB	-0.04% ⬇️	-144	+8	0
`use_rust/pi_pico_w_ble`	672.6 KiB	673.2 KiB	+0.09% ⬆️	+368	0	+272
`use_rust/rp2040`	145.5 KiB	145.5 KiB	+0.00%	0	0	0
`use_rust/rp2040_split (central)`	158.4 KiB	158.4 KiB	+0.00%	0	0	0
`use_rust/rp2040_split (peripheral)`	28.2 KiB	28.2 KiB	+0.00%	0	0	0
`use_rust/stm32f1`	61.9 KiB	61.9 KiB	+0.00% ⬇️	-4	0	0
`use_rust/stm32h7`	119.3 KiB	119.3 KiB	+0.00% ⬆️	+4	0	0

use_config/nrf52832_ble — 398.4 KiB → 398.7 KiB (+0.07% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 365720	   8620	  33952	 408292	  63ae4	rmk-nrf52832

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 365676	   8620	  33680	 407976	  639a8	rmk-nrf52832

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +2.84Ki  [ = ]       0    .debug_str
  +0.1% +2.44Ki  [ = ]       0    .debug_info
  +0.1%    +766  [ = ]       0    .debug_loc
  +0.1%    +339  [ = ]       0    .strtab
  [ = ]       0  +0.8%    +272    .bss
  +0.0%     +64  [ = ]       0    .debug_ranges
  +0.1%     +64  [ = ]       0    .symtab
  +0.1%     +44  [ = ]       0    .debug_frame
  +0.0%     +28  +0.0%     +28    .text
  +0.1%     +24  [ = ]       0    .debug_aranges
  +0.0%     +16  +0.0%     +16    .rodata
  +0.0%      +1  [ = ]       0    .debug_line
 -21.1%     -12  [ = ]       0    [Unmapped]
  +0.1% +6.59Ki  +0.1%    +316    TOTAL

use_config/nrf52840_ble — 440.6 KiB → 440.8 KiB (+0.03% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 398748	   8628	  43984	 451360	  6e320	rmk-nrf52840

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 398856	   8628	  43712	 451196	  6e27c	rmk-nrf52840

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +2.41Ki  [ = ]       0    .debug_str
  +0.1% +1.62Ki  [ = ]       0    .debug_info
  +0.1%    +514  [ = ]       0    .strtab
  +0.1%    +277  [ = ]       0    .debug_line
  [ = ]       0  +0.6%    +272    .bss
  +0.2%    +224  [ = ]       0    .symtab
  +0.2%    +108  [ = ]       0    .debug_frame
  +0.1%     +56  [ = ]       0    .debug_aranges
  +0.5%     +39  [ = ]       0    .debug_abbrev
  +0.0%     +16  +0.0%     +16    .rodata
   +30%     +15  [ = ]       0    [Unmapped]
  -0.0%    -124  -0.0%    -124    .text
  -0.3%    -728  [ = ]       0    .debug_ranges
  -0.4% -2.87Ki  [ = ]       0    .debug_loc
  +0.0% +1.56Ki  +0.0%    +164    TOTAL

use_config/nrf52840_ble_split (central) — 502.5 KiB → 506.3 KiB (+0.75% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 459652	   8684	  50136	 518472	  7e948	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 456836	   8684	  49056	 514576	  7da10	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +1.2% +56.5Ki  [ = ]       0    .debug_str
  +1.1% +25.1Ki  [ = ]       0    .debug_info
  +0.8% +7.00Ki  [ = ]       0    .debug_loc
  +2.0% +4.90Ki  [ = ]       0    .debug_ranges
  +0.6% +2.49Ki  +0.6% +2.49Ki    .text
  +0.7% +2.44Ki  [ = ]       0    .debug_line
  +0.5% +2.16Ki  [ = ]       0    .strtab
  [ = ]       0  +2.2% +1.05Ki    .bss
  +0.7%   +1024  [ = ]       0    .symtab
  +1.1%    +580  [ = ]       0    .debug_frame
  +0.6%    +268  +0.6%    +268    .rodata
  +0.5%    +232  [ = ]       0    .debug_aranges
  -3.0%      -2  [ = ]       0    [Unmapped]
  -0.6%     -48  [ = ]       0    .debug_abbrev
  +1.0%  +102Ki  +0.8% +3.80Ki    TOTAL

use_config/nrf52840_ble_split (peripheral) — 317.5 KiB → 317.5 KiB (-0.01% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 291396	   8508	  25184	 325088	  4f5e0	peripheral

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 291464	   8500	  25184	 325148	  4f61c	peripheral

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +3.59Ki  [ = ]       0    .debug_str
  +0.1%   +1021  [ = ]       0    .debug_info
  +0.2%     +16  [ = ]       0    .debug_abbrev
  +0.1%      +8  +0.1%      +8    .data
  -4.1%      -2  [ = ]       0    [Unmapped]
  -0.0%     -68  -0.0%     -68    .text
  -0.2%     -80  [ = ]       0    .debug_aranges
  -0.0%    -116  [ = ]       0    .debug_line
  -0.9%    -296  [ = ]       0    .debug_frame
  -0.5%    -464  [ = ]       0    .symtab
  -0.5%    -808  [ = ]       0    .debug_ranges
  -0.5% -1.26Ki  [ = ]       0    .strtab
  -0.9% -4.75Ki  [ = ]       0    .debug_loc
  -0.0% -3.19Ki  -0.0%     -60    TOTAL

use_config/pi_pico_w_ble — 673.3 KiB → 673.9 KiB (+0.09% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 636076	      0	  54016	 690092	  a87ac	rmk-pi-pico-w

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 635720	      0	  53744	 689464	  a8538	rmk-pi-pico-w

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2% +1.85Ki  [ = ]       0    .debug_loc
  +0.1% +1.68Ki  [ = ]       0    .debug_info
  +0.0% +1.61Ki  [ = ]       0    .debug_str
  +0.3%    +728  [ = ]       0    .debug_ranges
  +0.1%    +368  [ = ]       0    .strtab
  +0.1%    +336  +0.1%    +336    .text
  +0.1%    +307  [ = ]       0    .debug_line
  [ = ]       0  +0.5%    +272    .bss
  +0.1%     +48  [ = ]       0    .symtab
  +0.1%     +28  [ = ]       0    .debug_frame
  +0.0%     +20  +0.0%     +20    .rodata
  +0.0%     +16  [ = ]       0    .debug_aranges
  -6.9%      -5  [ = ]       0    [Unmapped]
  -0.4%     -39  [ = ]       0    .debug_abbrev
  +0.1% +6.91Ki  +0.1%    +628    TOTAL

use_config/rp2040 — 146.1 KiB → 146.1 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 135672	      0	  13900	 149572	  24844	rmk-rp2040

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 135672	      0	  13900	 149572	  24844	rmk-rp2040

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [ = ]       0  [ = ]       0    TOTAL

use_config/rp2040_split (central) — 159.7 KiB → 159.7 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 148716	      0	  14844	 163560	  27ee8	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 148712	      0	  14844	 163556	  27ee4	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +19  [ = ]       0    .debug_info
  +0.0%      +4  +0.0%      +4    .text
  +0.0%      +3  [ = ]       0    .debug_line
  +0.0%      +1  [ = ]       0    .debug_str
 -16.3%      -7  [ = ]       0    [Unmapped]
  +0.0%     +20  +0.0%      +4    TOTAL

use_config/rp2040_split (peripheral) — 27.9 KiB → 27.9 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  25696	     60	   2804	  28560	   6f90	peripheral

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  25696	     60	   2804	  28560	   6f90	peripheral

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%      +5  [ = ]       0    .debug_info
  +0.0%      +1  [ = ]       0    .debug_str
  -3.9%      -2  [ = ]       0    [Unmapped]
  +0.0%      +4  [ = ]       0    TOTAL

use_config/stm32f1 — 62.7 KiB → 62.7 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  57784	     28	   6360	  64172	   faac	rmk-stm32f1

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  57784	     28	   6360	  64172	   faac	rmk-stm32f1

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [ = ]       0  [ = ]       0    TOTAL

use_config/stm32h7 — 100.9 KiB → 100.9 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  94908	    264	   8112	 103284	  19374	rmk-stm32h7

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  94904	    264	   8112	 103280	  19370	rmk-stm32h7

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +1.34Ki  [ = ]       0    .debug_str
  +0.2%    +108  [ = ]       0    .strtab
  +0.0%      +4  +0.0%      +4    .text
  -4.5%      -2  [ = ]       0    [Unmapped]
  -0.0%     -52  [ = ]       0    .debug_info
  +0.0% +1.40Ki  +0.0%      +4    TOTAL

use_rust/nrf52832_ble — 385.7 KiB → 386.8 KiB (+0.26% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 353544	   8620	  33896	 396060	  60b1c	rmk-nrf52832

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 352752	   8620	  33624	 394996	  606f4	rmk-nrf52832

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.5% +3.07Ki  [ = ]       0    .debug_loc
  +0.1% +1.83Ki  [ = ]       0    .debug_info
  +0.0% +1.51Ki  [ = ]       0    .debug_str
  +0.3%    +842  [ = ]       0    .strtab
  +0.2%    +776  +0.2%    +776    .text
  +0.5%    +640  [ = ]       0    .symtab
  +0.1%    +413  [ = ]       0    .debug_line
  +0.7%    +316  [ = ]       0    .debug_frame
  [ = ]       0  +0.8%    +272    .bss
  +0.4%    +152  [ = ]       0    .debug_aranges
  +0.0%     +16  +0.0%     +16    .rodata
  +9.6%      +5  [ = ]       0    [Unmapped]
  -0.1%    -240  [ = ]       0    .debug_ranges
  +0.1% +9.25Ki  +0.3% +1.04Ki    TOTAL

use_rust/nrf52840_ble — 436.1 KiB → 436.2 KiB (+0.04% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 396876	   8628	  41216	 446720	  6d100	rmk-nrf52840

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 396948	   8628	  40944	 446520	  6d038	rmk-nrf52840

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +2.35Ki  [ = ]       0    .debug_info
  +0.1% +2.16Ki  [ = ]       0    .debug_str
  +0.1%    +309  [ = ]       0    .strtab
  [ = ]       0  +0.7%    +272    .bss
  +0.0%     +32  [ = ]       0    .symtab
  +0.0%     +16  +0.0%     +16    .rodata
  +0.0%     +12  [ = ]       0    .debug_frame
  +0.0%      +8  [ = ]       0    .debug_aranges
 -32.9%     -24  [ = ]       0    [Unmapped]
  -0.0%     -88  -0.0%     -88    .text
  -0.1%    -286  [ = ]       0    .debug_line
  -0.4%    -856  [ = ]       0    .debug_ranges
  -0.2% -1.55Ki  [ = ]       0    .debug_loc
  +0.0% +2.10Ki  +0.0%    +200    TOTAL

use_rust/nrf52840_ble_split (central) — 505.8 KiB → 508.4 KiB (+0.51% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 460264	   8684	  51688	 520636	  7f1bc	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 458252	   8684	  51008	 517944	  7e738	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.6% +30.3Ki  [ = ]       0    .debug_str
  +0.5% +11.3Ki  [ = ]       0    .debug_info
  +0.5% +4.43Ki  [ = ]       0    .debug_loc
  +0.8% +3.06Ki  [ = ]       0    .strtab
  +1.0% +2.44Ki  [ = ]       0    .debug_ranges
  +0.5% +1.93Ki  +0.5% +1.93Ki    .text
  +0.4% +1.53Ki  [ = ]       0    .debug_line
  [ = ]       0  +1.4%    +680    .bss
  +0.2%    +336  [ = ]       0    .symtab
  +0.3%    +188  [ = ]       0    .debug_frame
  +0.1%     +72  [ = ]       0    .debug_aranges
  +0.1%     +32  +0.1%     +32    .rodata
  -0.4%     -38  [ = ]       0    .debug_abbrev
  +0.6% +55.6Ki  +0.5% +2.63Ki    TOTAL

use_rust/nrf52840_ble_split (peripheral) — 315.3 KiB → 315.2 KiB (-0.04% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 289308	   8508	  24952	 322768	  4ecd0	peripheral

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 289452	   8500	  24952	 322904	  4ed58	peripheral

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +3.65Ki  [ = ]       0    .debug_str
  +0.1% +1.13Ki  [ = ]       0    .debug_info
  +0.2%     +16  [ = ]       0    .debug_abbrev
  +0.1%      +8  +0.1%      +8    .data
  +5.9%      +3  [ = ]       0    [Unmapped]
  -0.1%     -56  [ = ]       0    .debug_aranges
  -0.1%    -144  -0.1%    -144    .text
  -0.7%    -248  [ = ]       0    .debug_frame
  -0.1%    -334  [ = ]       0    .debug_line
  -0.4%    -400  [ = ]       0    .symtab
  -0.7% -1.14Ki  [ = ]       0    .debug_ranges
  -0.5% -1.19Ki  [ = ]       0    .strtab
  -0.4% -2.30Ki  [ = ]       0    .debug_loc
  -0.0%    -996  -0.0%    -136    TOTAL

use_rust/pi_pico_w_ble — 672.6 KiB → 673.2 KiB (+0.09% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 635700	      0	  53696	 689396	  a84f4	rmk-pi-pico-w

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 635332	      0	  53424	 688756	  a8274	rmk-pi-pico-w

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +1.88Ki  [ = ]       0    .debug_info
  +0.2% +1.85Ki  [ = ]       0    .debug_loc
  +0.3%    +728  [ = ]       0    .debug_ranges
  +0.1%    +431  [ = ]       0    .debug_line
  +0.1%    +352  +0.1%    +352    .text
  [ = ]       0  +0.5%    +272    .bss
  +0.1%     +48  [ = ]       0    .symtab
  +0.1%     +28  [ = ]       0    .debug_frame
   +45%     +19  [ = ]       0    [Unmapped]
  +0.0%     +16  [ = ]       0    .debug_aranges
  +0.0%     +16  +0.0%     +16    .rodata
  -0.1%    -285  [ = ]       0    .strtab
  -0.1% -3.21Ki  [ = ]       0    .debug_str
  +0.0% +1.85Ki  +0.1%    +640    TOTAL

use_rust/rp2040 — 145.5 KiB → 145.5 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 135300	      0	  13732	 149032	  24628	rmk-rp2040

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 135300	      0	  13732	 149032	  24628	rmk-rp2040

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%    +173  [ = ]       0    .debug_str
  +0.0%     +80  [ = ]       0    .debug_info
  +0.0%     +66  [ = ]       0    .debug_line
  +0.0%      +9  [ = ]       0    .strtab
  -4.4%      -2  [ = ]       0    [Unmapped]
  -0.0%     -10  [ = ]       0    .debug_loc
  +0.0%    +316  [ = ]       0    TOTAL

use_rust/rp2040_split (central) — 158.4 KiB → 158.4 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 147624	      0	  14588	 162212	  279a4	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 147624	      0	  14588	 162212	  279a4	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1%    +146  [ = ]       0    .debug_line
  +0.0%     +70  [ = ]       0    .debug_str
  +0.0%     +16  [ = ]       0    .debug_info
  +0.0%      +1  [ = ]       0    .strtab
  +2.3%      +1  [ = ]       0    [Unmapped]
  -0.0%     -10  [ = ]       0    .debug_loc
  +0.0%    +224  [ = ]       0    TOTAL

use_rust/rp2040_split (peripheral) — 28.2 KiB → 28.2 KiB (+0.00%)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  25796	     60	   3068	  28924	   70fc	peripheral

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  25796	     60	   3068	  28924	   70fc	peripheral

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%      +5  [ = ]       0    .debug_info
  +0.0%      +2  [ = ]       0    .debug_str
  +0.0%      +1  [ = ]       0    .strtab
  +0.0%      +8  [ = ]       0    TOTAL

use_rust/stm32f1 — 61.9 KiB → 61.9 KiB (+0.00% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  57120	     28	   6280	  63428	   f7c4	rmk-stm32f1

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  57124	     28	   6280	  63432	   f7c8	rmk-stm32f1

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +63  [ = ]       0    .debug_str
  +0.0%     +52  [ = ]       0    .debug_info
  +0.0%      +9  [ = ]       0    .strtab
  -0.0%      -4  -0.0%      -4    .text
  +0.0%    +120  -0.0%      -4    TOTAL

use_rust/stm32h7 — 119.3 KiB → 119.3 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 107796	    320	  14012	 122128	  1dd10	rmk-stm32h7

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 107792	    320	  14012	 122124	  1dd0c	rmk-stm32h7

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +10  [ = ]       0    .debug_loc
  +0.0%      +9  [ = ]       0    .strtab
  +0.0%      +6  [ = ]       0    .debug_info
  +0.0%      +4  +0.0%      +4    .text
 -10.4%      -7  [ = ]       0    [Unmapped]
  -0.0%     -37  [ = ]       0    .debug_str
  -0.1%    -137  [ = ]       0    .debug_line
  -0.0%    -152  +0.0%      +4    TOTAL

HaoboGu · 2026-08-11T03:55:56Z

Do you have any idea why Flash/RAM increases that much for split central?

…ry-gatt

kot149 · 2026-08-15T02:01:16Z

Do you have any idea why Flash/RAM increases that much for split central?

The largest avoidable cause was enabling trouble-host's 128-byte client ATT table for every split build, as you mentioned. I removed the default ATT table expansion and now generate Peripheral Battery Services only for peripherals with battery_adc_pin configured. This reduced the split central overhead as follows:

use_config: .text +4,920 -> +2,956 bytes, .data +128 -> 0 bytes, .bss +1,864 -> +1,080 bytes
use_rust: .text +4,136 -> +2,040 bytes, .data +128 -> 0 bytes, .bss +1,864 -> +680 bytes

The remaining increase comes from the new GATT descriptors and, when configured, the additional Battery Service and notification handling. The common +272 B .bss in BLE builds is mainly the cost of the two new descriptors on the central Battery Level characteristic. Split peripheral builds now have no .bss increase.

HaoboGu

It looks good! I have only 1 more comment: when the split peripheral disconnects, will the battery level for peripheral be set to 0 or marked disconnected somehow?

kot149 · 2026-08-19T14:51:32Z

when the split peripheral disconnects, will the battery level for peripheral be set to 0 or marked disconnected somehow?

The Battery Service does not have a standard value for "disconnected" or "unknown", and 0 means an actual 0% battery level.
Currently, the last reported battery level is kept until the central is restarted, and when the central starts up with the peripheral disconnected, the GATT Battery Level remains at its initial value of 0%, since the last reported value is only stored in RAM. This might seem inconsistent, but treating 0% as disconnected also feels unnatural to me.

HaoboGu · 2026-08-19T14:58:55Z

That's fine, thank you very much for your effort! I'm merging it

alxzh · 2026-08-20T01:18:33Z

How did you make it show up in the zmk-battery-center? Does it require any special configuration?

kot149 · 2026-08-20T04:06:46Z

@alxzh

How did you make it show up in the zmk-battery-center? Does it require any special configuration?

No special configuration is required; only battery_adc_pin for your split peripheral is needed (battery_user_description is optional).
Updating the GATT structure might require re-pairing the BLE host.

kot149 added 3 commits August 9, 2026 21:21

feat: expose peripheral battery level via central GATT

3777a8a

feat(ble): add configurable battery user descriptions

00f55f2

docs: update changelog for battery GATT features

7cb7ca6

kot149 force-pushed the feat/peripheral-battery-gatt branch from d071129 to 7cb7ca6 Compare August 9, 2026 12:24

kot149 marked this pull request as ready for review August 9, 2026 14:49

HaoboGu reviewed Aug 10, 2026

View reviewed changes

Comment thread rmk-config/src/resolved/build_constants.rs Outdated

Comment thread rmk-config/src/resolved/build_constants.rs Outdated

refactor(ble): rely on trouble-host GATT capacity checks

7b85aae

HaoboGu reviewed Aug 11, 2026

View reviewed changes

kot149 added 4 commits August 15, 2026 09:34

fix(ble): only expose configured split peripheral batteries

39b12cb

refactor(ble): configure client ATT capacity per project

5070547

Merge remote-tracking branch 'origin/main' into feat/peripheral-batte…

11bae7e

…ry-gatt

fix(ble): avoid clippy lint for empty battery services

fb06ab2

HaoboGu reviewed Aug 17, 2026

View reviewed changes

Comment thread rmk/src/ble/battery_service.rs Outdated

Comment thread rmk-config/src/resolved/build_constants.rs

HaoboGu reviewed Aug 17, 2026

View reviewed changes

Comment thread rmk/src/ble/battery_service.rs Outdated

kot149 added 4 commits August 18, 2026 22:53

refactor(ble): clarify battery presentation format constants

c5defe9

fix(config): reject unnamed peripheral battery descriptions

de175b5

refactor(ble): simplify peripheral battery services

edc1390

fix(config): gate split battery validation by feature

5358a87

HaoboGu reviewed Aug 19, 2026

View reviewed changes

HaoboGu merged commit f8da274 into rmk-rs:main Aug 19, 2026
62 checks passed

kot149 deleted the feat/peripheral-battery-gatt branch August 19, 2026 14:59

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kot149 commented Aug 9, 2026

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