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[Sponsored by FlightWave] Enable more than one DShot timer on STM32H7 #26013

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[Sponsored by FlightWave] Enable more than one DShot timer on STM32H7 #26013

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@julianoes julianoes commented Nov 28, 2025 •
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This extends DShot and Bidirectional DShot to more than one timer.

So far I have tested this on a CubeOrange with 6 outputs (AUX 1-4 on timer 1, AUX 5-6 on timer 4).

nsh> dshot status
INFO  [dshot] Outputs initialized: yes
INFO  [dshot] Outputs used: 0x3f
INFO  [dshot] Outputs on: yes
dshot: cycle: 41433 events, 1187949us elapsed, 28.67us avg, min 24us max 150us 2.546us rms
dshot: bdshot rpm: 20718 events
dshot: dshot telem: 0 events
INFO  [mixer_module] Param prefix: PWM_AUX
control latency: 41433 events, 9900016us elapsed, 238.94us avg, min 228us max 491us 7.134us rms
INFO  [mixer_module] Switched to rate_ctrl work queue
Channel Configuration:
Channel 0: func: 101, value: 109, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
Channel 1: func: 102, value: 317, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
Channel 2: func:   0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
Channel 3: func:   0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
Channel 4: func: 103, value: 430, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
Channel 5: func: 104, value: 676, failsafe: 0, disarmed: 0, min: 109, max: 1999, center: 65535
INFO  [arch_dshot] dshot driver stats:
INFO  [arch_dshot] Bidirectional DShot enabled on 2 timer(s)
INFO  [arch_dshot] Output 0: eRPM 172, read 19816, failed nibble 0, failed CRC 0, invalid/zero 902
INFO  [arch_dshot] Output 1: eRPM 426, read 19817, failed nibble 0, failed CRC 0, invalid/zero 902
INFO  [arch_dshot] Output 2: eRPM 0, read 0, failed nibble 0, failed CRC 0, invalid/zero 0
INFO  [arch_dshot] Output 3: eRPM 0, read 0, failed nibble 0, failed CRC 0, invalid/zero 0
INFO  [arch_dshot] Output 4: eRPM 581, read 19817, failed nibble 0, failed CRC 0, invalid/zero 903
INFO  [arch_dshot] Output 5: eRPM 845, read 19822, failed nibble 0, failed CRC 0, invalid/zero 902

@julianoes julianoes requested a review from dakejahl November 28, 2025 01:37
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github-actions bot commented Nov 28, 2025 •
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🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: 1588 byte (0.07 %)] 
    FILE SIZE        VM SIZE    
--------------  -------------- 
[ = ]       0  +1.6% +1.38Ki    .bss
  [ = ]       0  +400%   +1024    dshot_capture_buffer
  [ = ]       0  [NEW]    +160    _cc_calls
  [ = ]       0  +400%     +64    read_fail_crc
  [ = ]       0  +400%     +64    read_fail_nibble
  [ = ]       0  +400%     +64    read_fail_zero
  [ = ]       0  +320%     +64    read_ok
  [ = ]       0 +11e2%     +11    _bidirectional
  [ = ]       0  [NEW]      +5    _bidi_timer_indices
  [ = ]       0  [NEW]      +3    _num_bidi_timers
  [ = ]       0  [DEL]     -19    [section .bss]
  [ = ]       0  [DEL]     -32    _cc_call
+0.0%    +176  +0.0%    +176    .text
   +18%     +76   +18%     +76    dma_burst_finished_callback
   +38%     +56   +38%     +56    up_bdshot_status
  +6.1%     +32  +6.1%     +32    capture_complete_callback
  [NEW]     +24  [NEW]     +24    CSWTCH.58
   +42%     +16   +42%     +16    DShot::update_num_motors()
  [NEW]     +12  [NEW]     +12    up_bdshot_set_active_channels
  -1.5%      -4  -1.5%      -4    build_gam_response()
  -0.6%      -4  -0.6%      -4    up_dshot_init
  -0.0%      -8  -0.0%      -8    [section .text]
  [DEL]     -24  [DEL]     -24    CSWTCH.62
+0.1%      +4  +0.1%      +4    .data
  [NEW]      +4  [NEW]      +4    _bdshot_active_channels
+0.0%     +65  [ = ]       0    .debug_abbrev
+0.0%      +8  [ = ]       0    .debug_aranges
+0.0%     +36  [ = ]       0    .debug_frame
+0.0%    +493  [ = ]       0    .debug_info
+0.0%    +126  [ = ]       0    .debug_line
  [DEL]      -1  [ = ]       0    [Unmapped]
  +0.0%    +127  [ = ]       0    [section .debug_line]
+0.0%    +171  [ = ]       0    .debug_loclists
+0.0%     +92  [ = ]       0    .debug_rnglists
+0.0%     +81  [ = ]       0    .debug_str
+0.0%     +92  [ = ]       0    .strtab
  [NEW]     +10  [ = ]       0    CSWTCH.58
  [DEL]     -10  [ = ]       0    CSWTCH.62
 -44.4%     -16  [ = ]       0    __sched_lock_veneer
   +59%     +16  [ = ]       0    __stm32_dmaresidual_veneer
  [NEW]     +24  [ = ]       0    _bdshot_active_channels
  [NEW]     +20  [ = ]       0    _bidi_timer_indices
  [DEL]      -9  [ = ]       0    _cc_call
  [NEW]     +10  [ = ]       0    _cc_calls
  [NEW]     +17  [ = ]       0    _num_bidi_timers
  [NEW]     +30  [ = ]       0    up_bdshot_set_active_channels
+0.0%    +144  [ = ]       0    .symtab
  [NEW]     +32  [ = ]       0    CSWTCH.58
  [DEL]     -48  [ = ]       0    CSWTCH.62
 -40.0%     -32  [ = ]       0    __sched_lock_veneer
   +67%     +32  [ = ]       0    __stm32_dmaresidual_veneer
  [NEW]     +32  [ = ]       0    _bdshot_active_channels
  [NEW]     +32  [ = ]       0    _bidi_timer_indices
 -33.3%     -16  [ = ]       0    _bidirectional
  [DEL]     -32  [ = ]       0    _cc_call
  [NEW]     +32  [ = ]       0    _cc_calls
  [NEW]     +48  [ = ]       0    _num_bidi_timers
   +50%     +16  [ = ]       0    read_fail_nibble
 -25.0%     -16  [ = ]       0    up_bdshot_channel_status
  [NEW]     +64  [ = ]       0    up_bdshot_set_active_channels
-1.6%    -176  [ = ]       0    [Unmapped]
+0.0% +1.28Ki  +0.1% +1.55Ki    TOTAL
px4_fmu-v6x [Total VM Diff: 1656 byte (0.08 %)] 
    FILE SIZE        VM SIZE    
--------------  -------------- 
[ = ]       0  +1.5% +1.44Ki    .bss
  [ = ]       0  +400%   +1024    dshot_capture_buffer
  [ = ]       0  [NEW]    +160    _cc_calls
  [ = ]       0  +400%     +64    read_fail_crc
  [ = ]       0  +400%     +64    read_fail_nibble
  [ = ]       0  +400%     +64    read_fail_zero
  [ = ]       0  +320%     +64    read_ok
  [ = ]       0  +123%     +59    [section .bss]
  [ = ]       0  [NEW]      +5    _bidi_timer_indices
  [ = ]       0  [NEW]      +3    _num_bidi_timers
  [ = ]       0 -75.0%      -3    _bidirectional
  [ = ]       0  [DEL]     -32    _cc_call
+0.0%    +184  +0.0%    +184    .text
   +18%     +80   +18%     +80    dma_burst_finished_callback
   +38%     +56   +38%     +56    up_bdshot_status
  +6.1%     +32  +6.1%     +32    capture_complete_callback
  [NEW]     +24  [NEW]     +24    CSWTCH.59
   +42%     +16   +42%     +16    DShot::update_num_motors()
  [NEW]     +12  [NEW]     +12    up_bdshot_set_active_channels
  -0.6%      -4  -0.6%      -4    up_dshot_init
  -0.0%      -8  -0.0%      -8    [section .text]
 -50.0%     -24 -50.0%     -24    CSWTCH.63
+0.0%     +65  [ = ]       0    .debug_abbrev
+0.0%      +8  [ = ]       0    .debug_aranges
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+0.0%    +477  [ = ]       0    .debug_info
+0.0%    +162  [ = ]       0    .debug_line
  +300%      +3  [ = ]       0    [Unmapped]
  +0.0%    +159  [ = ]       0    [section .debug_line]
+0.0%    +286  [ = ]       0    .debug_loclists
+0.0%     +97  [ = ]       0    .debug_rnglists
 -33.3%      -1  [ = ]       0    [Unmapped]
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+0.9%      +2  [ = ]       0    .shstrtab
+0.0%    +102  [ = ]       0    .strtab
  [NEW]     +10  [ = ]       0    CSWTCH.59
  [NEW]     +24  [ = ]       0    _bdshot_active_channels
  [NEW]     +20  [ = ]       0    _bidi_timer_indices
  [DEL]      -9  [ = ]       0    _cc_call
  [NEW]     +10  [ = ]       0    _cc_calls
  [NEW]     +17  [ = ]       0    _num_bidi_timers
  [NEW]     +30  [ = ]       0    up_bdshot_set_active_channels
+0.0%    +144  [ = ]       0    .symtab
  [NEW]     +32  [ = ]       0    CSWTCH.59
 -60.0%     -48  [ = ]       0    CSWTCH.63
  [NEW]     +32  [ = ]       0    _bdshot_active_channels
  [NEW]     +32  [ = ]       0    _bidi_timer_indices
 -33.3%     -16  [ = ]       0    _bidirectional
  [DEL]     -32  [ = ]       0    _cc_call
  [NEW]     +32  [ = ]       0    _cc_calls
  [NEW]     +48  [ = ]       0    _num_bidi_timers
   +50%     +16  [ = ]       0    read_fail_nibble
 -25.0%     -16  [ = ]       0    up_bdshot_channel_status
  [NEW]     +64  [ = ]       0    up_bdshot_set_active_channels
-2.6%    -184  [ = ]       0    [Unmapped]
+0.0% +1.43Ki  +0.1% +1.62Ki    TOTAL

Updated: 2025-12-02T17:43:45

@dakejahl dakejahl mentioned this pull request Nov 30, 2025
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@julianoes
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julianoes commented Dec 1, 2025

Tested on Holybro Kakute H7 dualimu with 8 DShot outputs over 4 timers with 2 channels each, works as well!

@dirksavage88
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dirksavage88 commented Dec 2, 2025

Hey @julianoes we did something similar for the nxp tropic board

We should probably get a log with a multicopter using dshot across the different timers.

@julianoes
dshot: extend to more than 1 timer for STM32H7
05b6903 
This extends dshot and bidir dshot to more than one timer.
@julianoes
dshot: improve status output
1649b5b 
This now shows the channels in output order rather than timer channel
order, and while at it, shows the actual eRPM read.
@julianoes
dshot: don't try to read inactive channels
1b08638 
If there is no ESCs connected on a timer channel, we don't need to go
through it when doing the round robin eRPM read.
@julianoes
dshot: update wrong comment regarding DMA usage
2593b18
@julianoes julianoes force-pushed the pr-bidir-more-timer branch from 5ce65b4 to 2593b18 Compare December 2, 2025 17:34
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