Change default pin for RA_HOMING_SENSOR_PIN to pin 3 on mksgenlv21

[JakobPetersson]

I am proposing to change the default pin for hall sensor from 53 to 3.

The board is designed to use pin 3 for homing the X-axis motor (RA-axis on OAT). And when using a hall sensor the 3-pin JST connector work perfectly in this port without splitting the cable to connect signal, voltage and ground in different places. It is a clean install.

Premise: This change is based on the premise that the most common use-case would be to only use one method of homing per axis (at a time).

My assumption is that you would reasonably only use either a hall sensor for very exact homing, an endstop, or the TMC sensorless homing (If it is implemented).

On mksgenlv21 a jumper controls if the diag-pin is connected to pin 3 or not. Jumper missing, free to use for hall sensor. Jumper in place, connected to X-diag in use for potential sensorless homing with TMC stepper.

Other: This wiki page would need to be updated along with this change: https://wiki.openastrotech.com/OpenAstroTracker/Addons/RAHallSensor

[openastrotech-bot]

Looks like your PR has code that needs to be changed in order to meet our coding standards! Here are your options:

1. Apply the patch that was generated by the job
   1. Click details under the failing clang-format check
   2. Click the Artifacts dropdown in the top right
   3. Download + unzip the clang-format-diff.patch file into the OpenAstroTracker-Firmware repo
   4. Run git apply clang-format-diff.patch to make the changes
   5. Commit and push up the formatted code
2. Run clang-format locally
   1. Run the command bash -c 'shopt -s nullglob globstar;GLOBIGNORE=./src/libs/TimerInterrupt/*; for i in ./{.,src/**,unit_tests,boards/**}/*.{c,cpp,h,hpp}; do clang-format -i $i; done'
   2. Commit and push up the formatted code

[JakobPetersson]

Rebased on 1.11.5 from develop branch.

[CTetford]

We discussed this internally and agree with your reasoning, but each of the X/Y/Z min/max pins have been allocated already for future features (they're shared with the diag pins).

X-min/max and Z-min/max are going to be used for limit switches for each axis on the OAM. Y-min/max are already used for the separate debug serial port which is needed for development purposes.

The best alternative is pin D11. It is adjacent to a 5V and gnd pin, so a single 3-pin Dupont connector can be used for the hall sensor.

Please change the pin and version number to the next available increment and we'll get this merged.

[JakobPetersson]

I believe I have made the requested changes now. @CTetford