dshot: Telem set baudrate before pin-swapping

[PetervdPerk-NXP]

@niklaut I've finally got the hardware to test #24706.

However on IMXRT setbaudrate resets the TIOCSSINGLEWIRE state it seems.
First setting baudrate and then TIOCSSINGLEWIRE fixes it for me.

[github-actions]

🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: 64 byte (0 %)]

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--------------  -------------- 
+0.0%     +64  +0.0%     +64    .text
  +0.0%     +40  +0.0%     +40    [section .text]
   +16%     +24   +16%     +24    DShotTelemetry::init()
+0.0%     +94  [ = ]       0    .debug_abbrev
-0.0%      -8  [ = ]       0    .debug_frame
+0.0%     +57  [ = ]       0    .debug_info
+0.0%     +17  [ = ]       0    .debug_line
  +100%      +2  [ = ]       0    [Unmapped]
  +0.0%     +15  [ = ]       0    [section .debug_line]
+0.0%     +12  [ = ]       0    .debug_loclists
-0.7%     -64  [ = ]       0    [Unmapped]
+0.0%    +172  +0.0%     +64    TOTAL

px4_fmu-v6x [Total VM Diff: 56 byte (0 %)]

    FILE SIZE        VM SIZE    
--------------  -------------- 
+0.0%     +56  +0.0%     +56    .text
  +0.0%     +32  +0.0%     +32    [section .text]
   +16%     +24   +16%     +24    DShotTelemetry::init()
+0.0%     +94  [ = ]       0    .debug_abbrev
-0.0%      -8  [ = ]       0    .debug_frame
+0.0%     +57  [ = ]       0    .debug_info
+0.0%     +17  [ = ]       0    .debug_line
  +200%      +2  [ = ]       0    [Unmapped]
  +0.0%     +15  [ = ]       0    [section .debug_line]
+0.0%     +12  [ = ]       0    .debug_loclists
-0.7%     -56  [ = ]       0    [Unmapped]
+0.0%    +172  +0.0%     +56    TOTAL

Updated: 2025-06-17T12:31:59

[dk7xe]

Dshot telemetry successful tested on Tropic VMU

NuttShell (NSH) NuttX-12.9.0
nsh> dshot status
INFO [dshot] Outputs initialized: yes
INFO [dshot] Outputs used: 0xf
INFO [dshot] Outputs on: yes
dshot: cycle: 48673 events, 2404967us elapsed, 49.41us avg, min 12us max 277us 23.707us rms
INFO [mixer_module] Param prefix: PWM_MAIN
control latency: 48677 events, 8455398us elapsed, 173.70us avg, min 125us max 59249us 368.344us rms
INFO [mixer_module] Switched to rate_ctrl work queue
Channel Configuration:
Channel 0: func: 103, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 1: func: 101, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 2: func: 104, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 3: func: 102, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 4: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 5: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 6: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
Channel 7: func: 0, value: 0, failsafe: 0, disarmed: 0, min: 109, max: 1999
INFO [dshot] telemetry on: /dev/ttyS5
INFO [dshot] Number of successful ESC frames: 23106
INFO [dshot] Number of timeouts: 96
INFO [dshot] Number of CRC errors: 0
nsh>
dshot esc_info -m 1
INFO [dshot] ESC Type: KISS (unknown)
INFO [dshot] MCU Serial Number: xxxxxx-xxxxxx-xxxxxx-xxxxxx
INFO [dshot] Firmware version: 0.10�
INFO [dshot] Rotation Direction: reversed
INFO [dshot] 3D Mode: off
nsh>

[niklaut]

I tested your change on the FMUv6s (STM32H7) and it still works just fine.

nsh> dshot esc_info -m 1
INFO  [dshot] ESC Type: #TEKKO32_F4_4in1_H#
INFO  [dshot] MCU Serial Number: xxx
INFO  [dshot] Firmware version: 32.80
INFO  [dshot] Rotation Direction: normal
INFO  [dshot] 3D Mode: off
INFO  [dshot] Low voltage Limit: off
INFO  [dshot] Current Limit: unsupported
INFO  [dshot] LED 0: unsupported
INFO  [dshot] LED 1: unsupported
INFO  [dshot] LED 2: unsupported
INFO  [dshot] LED 3: unsupported