feat(ble): Enable Bluetooth LE Connection Subrating for split communication by tompre · Pull Request #1008 · rmk-rs/rmk

tompre · 2026-07-30T17:10:01Z

As promised a few months back, here is a first draft for enabling connection subrating support on the peripheral connection.

Initial Results

Using a subrating factor of 30 (equivalent to a connection interval of 225ms):

Central: 50–80 µA
Peripheral: ~30 µA

The latency to return to 7.5ms intervals is 225ms + 2×7.5ms (compared to 5–7 seconds when using standard connection updates).

This allows us to use sleep mode much more aggressively, as input lag only impacts the very first keystroke.

Open Questions / Next Steps

Fast Polling Loop (Resolved)
#886 introduced a fast polling loop (5ms) leading to 500–700 µA current draw on Central. (Tracked/resolved via #1010).
Central Max Latency
I adjusted Central max latency to match the subrating duration. Unsure what effect this has on OS-level support.
We will use max_latency = 30 for now and leave timing optimization for a later commit.
GATT Buffer Sizing (Resolved)
SplitMessage GATT messages were sending the entire buffer rather than just the encoded payload. Truncating to the encoded data allows faster resets of the subrate factor. (Merged via #1011).
- Reference: rmk/src/split/ble/peripheral.rs#L113-L116 and rmk/src/split/ble/central.rs#L449-L450.

github-actions · 2026-07-30T17:20:18Z

Size Report

Example	main	PR	Diff	.text	.bss
`use_config/nrf52832_ble`	398.4 KiB	398.4 KiB	+0.00% ⬇️	-20	0
`use_config/nrf52840_ble`	440.6 KiB	440.6 KiB	+0.00% ⬆️	+8	0
`use_config/nrf52840_ble_split (central)`	502.5 KiB	505.6 KiB	+0.61% ⬆️	+3240	-64
`use_config/nrf52840_ble_split (peripheral)`	317.5 KiB	320.2 KiB	+0.83% ⬆️	+2580	+144
`use_config/pi_pico_w_ble`	673.3 KiB	673.3 KiB	+0.00% ⬆️	+12	0
`use_config/rp2040`	146.1 KiB	146.1 KiB	+0.00%	0	0
`use_config/rp2040_split (central)`	159.8 KiB	159.8 KiB	+0.00% ⬆️	+4	0
`use_config/rp2040_split (peripheral)`	27.9 KiB	27.9 KiB	+0.00%	0	0
`use_config/stm32f1`	62.7 KiB	62.7 KiB	+0.00% ⬇️	-4	0
`use_config/stm32h7`	100.9 KiB	100.9 KiB	+0.00% ⬆️	+4	0
`use_rust/nrf52832_ble`	385.8 KiB	385.7 KiB	+0.00% ⬇️	-8	0
`use_rust/nrf52840_ble`	436.1 KiB	436.1 KiB	+0.00% ⬆️	+4	0
`use_rust/nrf52840_ble_split (central)`	505.8 KiB	507.7 KiB	+0.36% ⬆️	+2088	-200
`use_rust/nrf52840_ble_split (peripheral)`	315.3 KiB	316.1 KiB	+0.24% ⬆️	+776	+8
`use_rust/pi_pico_w_ble`	672.6 KiB	672.6 KiB	+0.00% ⬆️	+20	0
`use_rust/rp2040`	145.6 KiB	145.6 KiB	+0.00% ⬇️	-4	0
`use_rust/rp2040_split (central)`	158.4 KiB	158.4 KiB	+0.00%	0	0
`use_rust/rp2040_split (peripheral)`	28.2 KiB	28.2 KiB	+0.00%	0	0
`use_rust/stm32f1`	61.9 KiB	61.9 KiB	+0.00%	0	0
`use_rust/stm32h7`	119.3 KiB	119.3 KiB	+0.00% ⬇️	-4	0

use_config/nrf52832_ble — 398.4 KiB → 398.4 KiB (+0.00% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 365672	   8620	  33680	 407972	  639a4	rmk-nrf52832

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 365692	   8620	  33680	 407992	  639b8	rmk-nrf52832

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +69  [ = ]       0    .debug_info
  -0.0%      -9  [ = ]       0    .debug_line
  -0.0%     -11  [ = ]       0    .debug_str
 -20.3%     -15  [ = ]       0    [Unmapped]
  -0.0%     -17  [ = ]       0    .strtab
  -0.0%     -20  -0.0%     -20    .text
  -0.0%     -72  [ = ]       0    .debug_ranges
  -0.0%    -261  [ = ]       0    .debug_loc
  -0.0%    -336  -0.0%     -20    TOTAL

use_config/nrf52840_ble — 440.6 KiB → 440.6 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 398876	   8628	  43712	 451216	  6e290	rmk-nrf52840

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 398868	   8628	  43712	 451208	  6e288	rmk-nrf52840

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%    +286  [ = ]       0    .debug_info
  +0.1%    +232  [ = ]       0    .debug_line
  +0.0%    +126  [ = ]       0    .debug_loc
  +0.0%     +64  [ = ]       0    .debug_ranges
  +0.0%      +8  +0.0%      +8    .text
  -0.0%      -5  [ = ]       0    .strtab
 -12.5%      -9  [ = ]       0    [Unmapped]
  -0.0%     -22  [ = ]       0    .debug_str
  +0.0%    +680  +0.0%      +8    TOTAL

use_config/nrf52840_ble_split (central) — 502.5 KiB → 505.6 KiB (+0.61% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 460096	   8684	  48992	 517772	  7e68c	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 456856	   8684	  49056	 514596	  7da24	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2% +9.34Ki  [ = ]       0    .debug_str
  +0.3% +7.07Ki  [ = ]       0    .debug_info
  +0.6% +4.97Ki  [ = ]       0    .debug_loc
  +0.8% +3.05Ki  +0.8% +3.05Ki    .text
  +0.5% +1.95Ki  [ = ]       0    .strtab
  +0.8% +1.22Ki  [ = ]       0    .symtab
  +0.2%    +803  [ = ]       0    .debug_line
  +0.3%    +776  [ = ]       0    .debug_ranges
  +0.3%    +112  +0.3%    +112    .rodata
   +67%     +28  [ = ]       0    [Unmapped]
  +0.0%     +24  [ = ]       0    .debug_aranges
  -0.1%     -32  [ = ]       0    .debug_frame
  [ = ]       0  -0.1%     -64    .bss
  +0.3% +29.3Ki  +0.6% +3.10Ki    TOTAL

use_config/nrf52840_ble_split (peripheral) — 317.5 KiB → 320.2 KiB (+0.83% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 294044	   8500	  25328	 327872	  500c0	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    
 --------------  -------------- 
  +0.9% +2.36Ki  +0.9% +2.36Ki    .text
  +0.1% +1.93Ki  [ = ]       0    .debug_info
  +0.4% +1.05Ki  [ = ]       0    .strtab
  +0.9%    +976  [ = ]       0    .symtab
  +0.1%    +247  [ = ]       0    .debug_line
  +0.5%    +160  +0.5%    +160    .rodata
  +0.1%    +152  [ = ]       0    .debug_ranges
  [ = ]       0  +0.6%    +144    .bss
  +0.1%     +24  [ = ]       0    .debug_aranges
  +7.0%      +4  [ = ]       0    [Unmapped]
  -0.1%     -32  [ = ]       0    .debug_frame
  -0.1%    -785  [ = ]       0    .debug_loc
  -0.0%    -884  [ = ]       0    .debug_str
  +0.1% +5.21Ki  +0.8% +2.66Ki    TOTAL

use_config/pi_pico_w_ble — 673.3 KiB → 673.3 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 635752	      0	  53744	 689496	  a8558	rmk-pi-pico-w

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 635740	      0	  53744	 689484	  a854c	rmk-pi-pico-w

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +96  [ = ]       0    .debug_ranges
   +34%     +18  [ = ]       0    [Unmapped]
  +0.0%     +12  +0.0%     +12    .text
  -0.0%     -32  [ = ]       0    .symtab
  -0.0%     -33  [ = ]       0    .strtab
  -0.4%     -39  [ = ]       0    .debug_abbrev
  -0.0%    -100  [ = ]       0    .debug_line
  -0.0%    -173  [ = ]       0    .debug_info
  -0.0%    -185  [ = ]       0    .debug_loc
  -0.0%    -192  [ = ]       0    .debug_str
  -0.0%    -628  +0.0%     +12    TOTAL

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

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 135704	      0	  13900	 149604	  24864	rmk-rp2040

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 135704	      0	  13900	 149604	  24864	rmk-rp2040

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +10  [ = ]       0    .debug_loc
  -3.6%      -2  [ = ]       0    [Unmapped]
  -0.0%     -44  [ = ]       0    .debug_line
  -0.0%     -36  [ = ]       0    TOTAL

use_config/rp2040_split (central) — 159.8 KiB → 159.8 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 148748	      0	  14844	 163592	  27f08	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 148744	      0	  14844	 163588	  27f04	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%      +4  +0.0%      +4    .text
  -0.0%      -1  [ = ]       0    .strtab
  -7.3%      -3  [ = ]       0    [Unmapped]
  [ = ]       0  +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    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
  57788	     28	   6360	  64176	   fab0	rmk-stm32f1

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +64  [ = ]       0    .debug_str
  +0.0%     +52  [ = ]       0    .debug_info
  +0.0%      +9  [ = ]       0    .strtab
  +5.5%      +3  [ = ]       0    [Unmapped]
  -0.0%      -4  -0.0%      -4    .text
  +0.0%    +124  -0.0%      -4    TOTAL

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

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
  94928	    264	   8112	 103304	  19388	rmk-stm32h7

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
  94924	    264	   8112	 103300	  19384	rmk-stm32h7

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%      +4  +0.0%      +4    .text
  -6.7%      -4  [ = ]       0    [Unmapped]
  -0.0%      -9  [ = ]       0    .strtab
  -0.0%     -52  [ = ]       0    .debug_info
  -0.0%     -63  [ = ]       0    .debug_str
  -0.0%    -124  +0.0%      +4    TOTAL

use_rust/nrf52832_ble — 385.8 KiB → 385.7 KiB (+0.00% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 352760	   8620	  33624	 395004	  606fc	rmk-nrf52832

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 352768	   8620	  33624	 395012	  60704	rmk-nrf52832

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1%    +417  [ = ]       0    .debug_loc
  +0.1%    +112  [ = ]       0    .debug_ranges
  +0.0%     +57  [ = ]       0    .debug_info
  +0.0%     +32  [ = ]       0    .symtab
  +0.0%      +6  [ = ]       0    .strtab
  -0.0%      -8  -0.0%      -8    .text
  -0.0%     -13  [ = ]       0    .debug_line
 -34.8%     -23  [ = ]       0    [Unmapped]
  +0.0%    +580  -0.0%      -8    TOTAL

use_rust/nrf52840_ble — 436.1 KiB → 436.1 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 396972	   8628	  40944	 446544	  6d050	rmk-nrf52840

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 396968	   8628	  40944	 446540	  6d04c	rmk-nrf52840

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%    +215  [ = ]       0    .debug_info
  +0.0%    +126  [ = ]       0    .debug_loc
  +0.0%     +64  [ = ]       0    .debug_ranges
  +0.5%     +39  [ = ]       0    .debug_abbrev
  +0.0%      +8  [ = ]       0    .debug_str
  +0.0%      +4  +0.0%      +4    .text
  -3.8%      -2  [ = ]       0    [Unmapped]
  -0.0%      -7  [ = ]       0    .strtab
  -0.0%    -147  [ = ]       0    .debug_line
  +0.0%    +300  +0.0%      +4    TOTAL

use_rust/nrf52840_ble_split (central) — 505.8 KiB → 507.7 KiB (+0.36% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 460364	   8684	  50808	 519856	  7eeb0	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 458276	   8684	  51008	 517968	  7e750	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2% +8.01Ki  [ = ]       0    .debug_str
  +0.3% +6.13Ki  [ = ]       0    .debug_info
  +0.4% +3.47Ki  [ = ]       0    .debug_loc
  +0.5% +1.93Ki  +0.5% +1.93Ki    .text
  +0.3% +1.19Ki  [ = ]       0    .debug_line
  +0.3%    +768  [ = ]       0    .debug_ranges
  +0.2%    +723  [ = ]       0    .strtab
  +0.2%    +288  [ = ]       0    .symtab
  +0.2%    +112  +0.3%    +112    .rodata
  +0.0%     +24  [ = ]       0    .debug_aranges
  +0.9%      +8  [ = ]       0    .defmt
 -18.5%     -12  [ = ]       0    [Unmapped]
  -0.1%     -32  [ = ]       0    .debug_frame
  [ = ]       0  -0.4%    -200    .bss
  +0.2% +22.6Ki  +0.4% +1.84Ki    TOTAL

use_rust/nrf52840_ble_split (peripheral) — 315.3 KiB → 316.1 KiB (+0.24% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 290228	   8500	  24960	 323688	  4f068	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% +2.60Ki  [ = ]       0    .debug_str
  +0.1% +2.17Ki  [ = ]       0    .debug_info
  +0.2% +1.32Ki  [ = ]       0    .debug_loc
  +0.2%    +616  +0.2%    +616    .text
  +0.1%    +356  [ = ]       0    .strtab
  +0.1%    +319  [ = ]       0    .debug_line
  +0.2%    +256  [ = ]       0    .debug_ranges
  +0.2%    +208  [ = ]       0    .symtab
  +0.5%    +160  +0.5%    +160    .rodata
  +0.2%     +64  [ = ]       0    .debug_aranges
  +0.1%     +48  [ = ]       0    .debug_frame
   +42%     +21  [ = ]       0    [Unmapped]
  [ = ]       0  +0.0%      +8    .bss
  +0.1% +8.09Ki  +0.2%    +784    TOTAL

use_rust/pi_pico_w_ble — 672.6 KiB → 672.6 KiB (+0.00% ⬆️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 635368	      0	  53424	 688792	  a8298	rmk-pi-pico-w

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 635348	      0	  53424	 688772	  a8284	rmk-pi-pico-w

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +96  [ = ]       0    .debug_ranges
  +0.0%     +24  +0.0%     +24    .text
  -0.0%      -4  -0.0%      -4    .rodata
 -33.9%     -21  [ = ]       0    [Unmapped]
  -0.0%     -32  [ = ]       0    .symtab
  -0.0%     -33  [ = ]       0    .strtab
  -0.4%     -39  [ = ]       0    .debug_abbrev
  -0.0%    -103  [ = ]       0    .debug_line
  -0.0%    -136  [ = ]       0    .debug_info
  -0.0%    -175  [ = ]       0    .debug_loc
  -0.0%    -193  [ = ]       0    .debug_str
  -0.0%    -616  +0.0%     +20    TOTAL

use_rust/rp2040 — 145.6 KiB → 145.6 KiB (+0.00% ⬇️)

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 135332	      0	  13732	 149064	  24648	rmk-rp2040

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 135336	      0	  13732	 149068	  2464c	rmk-rp2040

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1%    +124  [ = ]       0    .debug_line
  +0.0%    +101  [ = ]       0    .debug_str
  +0.0%     +37  [ = ]       0    .debug_info
  +0.0%     +10  [ = ]       0    .debug_loc
   +18%      +7  [ = ]       0    [Unmapped]
  +0.0%      +1  [ = ]       0    .strtab
  -0.0%      -4  -0.0%      -4    .text
  +0.0%    +276  -0.0%      -4    TOTAL

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

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 147656	      0	  14588	 162244	  279c4	central

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 147656	      0	  14588	 162244	  279c4	central

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +19  [ = ]       0    .debug_line
  +0.0%     +12  [ = ]       0    .debug_loc
  -5.0%      -2  [ = ]       0    [Unmapped]
  -0.0%      -5  [ = ]       0    .strtab
  -0.0%     -36  [ = ]       0    .debug_str
  -0.0%     -40  [ = ]       0    .debug_info
  -0.0%     -52  [ = ]       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    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
  57120	     28	   6280	  63428	   f7c4	rmk-stm32f1

Bloaty diff (PR vs main):

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

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

cargo size (PR):

   text	   data	    bss	    dec	    hex	filename
 107836	    320	  14012	 122168	  1dd38	rmk-stm32h7

cargo size (main):

   text	   data	    bss	    dec	    hex	filename
 107840	    320	  14012	 122172	  1dd3c	rmk-stm32h7

Bloaty diff (PR vs main):

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +10  [ = ]       0    .debug_loc
  +6.4%      +3  [ = ]       0    [Unmapped]
  -0.0%      -4  -0.0%      -4    .text
  -0.0%     -37  [ = ]       0    .debug_info
  -0.0%    -100  [ = ]       0    .debug_str
  -0.1%    -124  [ = ]       0    .debug_line
  -0.0%    -252  -0.0%      -4    TOTAL

HaoboGu · 2026-07-31T02:50:25Z

#886 introduced a fast polling loop (5ms) which leads to 500-700uA of current draw in central. We should fix that anyway I think.

Yes, the fix looks fine

I changed Central max latency to be similarly long as the subrating. I'm unsure what this does with OS support.

I don't see any issue max_latency = 30

SplitMessage gatt messages always use the full buffer rather than only sending the encoded data, sending only the data might allow for faster resets of the subrate factor, if this was not done on purpose?

Yeah, only encoded buffer should be sent, that needs a fix. to_slice returns the encoded buf so the fix is easy.

The result is quite impressive! Thanks a lot for your effort!

tompre · 2026-08-06T12:03:38Z

I updated the description. With the work on #1027 and #1028 ongoing, I think I wait for them to merge before fixing conflicts.

HaoboGu · 2026-08-12T12:58:26Z

@tompre #1028 has landed, could you please rebase this branch onto the latest main? Code structure changed a lot(and I think it's better!)

tompre · 2026-08-18T15:04:01Z

The pull request should be ready:

I added docs
I added different settings for connected sleep vs. not-connected sleep. => Central will now have the same current draw as the peripheral when not connected.
I enabled the feature for the nrf52840_ble_split examples so it gets checked.

HaoboGu

Fantastic! It looks great.

Could you also add a table of the default connection parameters/subrating parameters somewhere?

tompre · 2026-08-18T17:19:33Z

Fantastic! It looks great.

Thanks.

Could you also add a table of the default connection parameters/subrating parameters somewhere?

Of course, where should I put it? In the docs? or in split/ble/central.rs?

I also did some measurements:

* Current draw on central with subrating
During sleep:
| max l. (HC) | in [ms] | SubF (SC) | in [ms] | avg. [µA] | KP latency [ms] |
|-------------+---------+-----------+---------+-----------+-----------------|
|          30 |    225. |        30 |    225. |        75 |           232.5 |
|          60 |    450. |        30 |    225. |        59 |           232.5 |
|         180 |   1350. |        30 |    225. |        48 |           232.5 |
|         300 |   2250. |        30 |    225. |        48 |           232.5 |
|          30 |    225. |        60 |    450. |        63 |           457.5 |
|          60 |    450. |        60 |    450. |        48 |           457.5 |
|         180 |   1350. |        60 |    450. |        39 |           457.5 |
|         300 |   2250. |        60 |    450. |        39 |           457.5 |
|         300 |   2250. |       120 |    900. |        32 |           907.5 |
#+TBLFM: $2=$-1*7.5::$4=$-1*7.5::$6=($3+1)*7.5
HC ... Host Connection
SC ... Split Connection
KP ... Key Press

In active mode without pressing any key, the average current is: ~600µA

* Current draw on peripheral with subrating
During Sleep with subrate factor: 60 and max_latency: 7, witch leads to a max
sleep time of 3.6s, the average current is: 21µA

In active mode without pressing any key, the average current depends on the max
latency of the split connection:
| max_latency |  [ms] | avg. [µA] |
|-------------+-------+-----------|
|          10 |   75. |        72 |
|          30 |  225. |        38 |
|          60 |  450. |        30 |
|         300 | 2250. |        21 |
#+TBLFM: $2=$-1*7.5

HaoboGu · 2026-08-18T18:02:00Z

I prefer to put it in split/ble/central.rs because it's a developer oriented info

HaoboGu · 2026-08-19T04:16:19Z

And the result is quite impressive! Could you also test the avg current when SC=10？

HaoboGu · 2026-08-20T15:26:16Z

@tompre I'm merging it now, thanks very much for bringing this feature to RMK!

This was referenced Jul 31, 2026

Regression on central power usage #1010

Closed

fix(ble): send exact payload size for SplitMessage #1011

Merged

tompre force-pushed the subrating branch from 27c910c to 048348b Compare August 3, 2026 08:12

tompre force-pushed the subrating branch 2 times, most recently from 30443eb to f0ef276 Compare August 18, 2026 14:58

tompre marked this pull request as ready for review August 18, 2026 14:59

tompre added 2 commits August 18, 2026 17:16

feat(ble): implement connection subrating for split keyboards

0eb6e89

docs(low-power): Add docs for BLE Connection Subrating

2265985

tompre force-pushed the subrating branch from f0ef276 to 2265985 Compare August 18, 2026 15:20

HaoboGu approved these changes Aug 18, 2026

View reviewed changes

HaoboGu merged commit bebabdf into rmk-rs:main Aug 20, 2026
62 checks passed

tompre deleted the subrating branch August 20, 2026 16:36

tompre mentioned this pull request Aug 20, 2026

refactor(ble): Improve power consumption, code structure and documentation of subrating config #1077

Open

Navigation Menu

Uh oh!

Uh oh!

feat(ble): Enable Bluetooth LE Connection Subrating for split communication - #1008

feat(ble): Enable Bluetooth LE Connection Subrating for split communication#1008
HaoboGu merged 2 commits into
rmk-rs:mainfrom
tompre:subrating

tompre commented Jul 30, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Jul 30, 2026 •

edited

Loading

Uh oh!

HaoboGu commented Jul 31, 2026 •

edited

Loading

Uh oh!

tompre commented Aug 6, 2026

Uh oh!

HaoboGu commented Aug 12, 2026 •

edited

Loading

Uh oh!

tompre commented Aug 18, 2026

Uh oh!

HaoboGu left a comment

Uh oh!

tompre commented Aug 18, 2026 •

edited

Loading

Uh oh!

HaoboGu commented Aug 18, 2026

Uh oh!

HaoboGu commented Aug 19, 2026

Uh oh!

HaoboGu commented Aug 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Uh oh!

Conversation

tompre commented Jul 30, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Initial Results

Open Questions / Next Steps

Uh oh!

github-actions Bot commented Jul 30, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Size Report

Uh oh!

HaoboGu commented Jul 31, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

tompre commented Aug 6, 2026

Uh oh!

HaoboGu commented Aug 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

tompre commented Aug 18, 2026

Uh oh!

HaoboGu left a comment

Choose a reason for hiding this comment

Uh oh!

tompre commented Aug 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

HaoboGu commented Aug 18, 2026

Uh oh!

HaoboGu commented Aug 19, 2026

Uh oh!

HaoboGu commented Aug 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

tompre commented Jul 30, 2026 •

edited

Loading

github-actions Bot commented Jul 30, 2026 •

edited

Loading

HaoboGu commented Jul 31, 2026 •

edited

Loading

HaoboGu commented Aug 12, 2026 •

edited

Loading

tompre commented Aug 18, 2026 •

edited

Loading