[Accton][wedge800bact] Calibrate HSC and ADC XP3R3V scaling in sensor_service.json

[ec-michael-shih]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running
  pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

clang-format.........................................(no files to check)Skipped
black................................................(no files to check)Skipped
shellcheck...........................................(no files to check)Skipped
shfmt................................................(no files to check)Skipped
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check json...............................................................Passed
check for merge conflicts................................................Passed
ruff check...........................................(no files to check)Skipped

Summary

In the sensor_service.json of Wedge800BACT, the compute value methods for voltage, current and power monitoring within the pmUnitScoped sections, which interface with the kernel drivers, need to be adjusted.

• Calibrate XP3R3V telemetry in sensor_service.json by adjusting ADC128D818 compute formula.
• Calibrate HSC scaling factor in sensor_service.json for 0.25mΩ ($R_{sense}$).

1. ADC128D818 Kernel Driver
   The conversion formula for the XP3R3V voltage input under pmUnitScopedName needs to be modified for the adc128d818 driver.
   --
   Original: "compute": "(8/5)@/1000"
   Updated: "compute": "(5/3)@/1000"
   --

2. LTC4287 Kernel Driver
   The conversion formulas for the HSC (Hot Swap Controller) current and power values under pmUnitScopedName need to be adjusted for the ltc4287 driver.
   --
   Original: "compute": "(3/5)@/1000"
   Updated: "compute": "(6/5)@/1000"
   --

Modification Rationale:
The default $R_{sense}$ value used in the kernel driver's internal calculation formula is $0.3\text{ m}\Omega$.
(Reference: drivers/hwmon/pmbus/ltc4286.c)
However, based on our hardware specifications, the actual sensing circuit utilizes two $0.5\text{ m}\Omega$ resistors in parallel, resulting in an effective total resistance ($R_{total}$) of $0.25\text{ m}\Omega$.
To compensate for this hardware difference, the scaling factor must be adjusted as follows:


.
$$\text{Correction Factor} = \frac{\text{Driver Default } R_{sense}}{\text{Actual Hardware } R_{sense}} = \frac{0.3\text{ m}\Omega}{0.25\text{ m}\Omega} = 1.2 \text{ (which is } 6/5)$$
.
Therefore, the compute value is updated to $(6/5)$ to ensure accurate data reporting.

Test Plan

1. Start sensor_service and ensure all sensor values can be read without errors.
   w800b_20260112_sensor_service.txt
2. Execute sensor_service_hw_test and confirm that all test items pass.
   w800b_20260112_sensor_service_hw_test.txt
3. Execute sensor_service_client command and confirmed that all test items passed.
   w800b_20260112_sensor_service_client.txt

Furthermore, by observing the data from the sensor_service_client command,
I verified that the values for the modified items mentioned above are consistent with our expected results.

|name | before | after |
| MCB_U33_XP3R3V_MCB | 3.19 | 3.33 |
| MCB_U33_XP3R3V_FCB | 3.19 | 3.32 |
| MCB_U33_XP3R3V_IOB | 3.19 | 3.32 |
| SMB_U42_XP3R3V | 3.20 | 3.33 |
| MCB_U41_HSC_PIN |288.40 |578.80 |
| MCB_U41_HSC_IOUT | 5.32 | 10.68 |