Document low_pass_filter.h with doxygen docstring

Closes #55

Author: taisirhassan

include/low_pass_filter.h

@@ -1,3 +1,12 @@
+/**
+ * @file
+ * @brief Low-pass filter implementation
+ *
+ * This module provides a low-pass filter implementation for smoothing sensor readings
+ * and reducing noise in analog signals. The filter uses an exponential moving average
+ * algorithm with configurable response time.
+ */
+
 #ifndef ROCKETLIB_LOW_PASS_FILTER_H
 #define ROCKETLIB_LOW_PASS_FILTER_H
 
@@ -10,22 +19,58 @@
 extern "C" {
 #endif
 
-// Inline function to calculate the sample frequency based on the time difference in milliseconds
+/**
+ * @brief Calculate the sample frequency based on the time difference in milliseconds
+ *
+ * @param time_diff_ms Time difference between samples in milliseconds
+ * @return double Sample frequency in Hz
+ */
 static inline double sample_freq(double time_diff_ms) {
 	return 1000.0 / time_diff_ms;
 }
 
-// Inline function to calculate the alpha value for the low-pass filter based on the response time
+/**
+ * @brief Calculate the alpha value for the low-pass filter based on the response time
+ *
+ * The alpha value determines the filter's responsiveness. A higher alpha value results
+ * in faster response but less filtering, while a lower alpha value provides more filtering
+ * but slower response.
+ *
+ * @param TR Response time constant in milliseconds
+ * @param time_diff_ms Time difference between samples in milliseconds
+ * @return double Alpha value (0.0 to 1.0) for the low-pass filter
+ */
 static inline double low_pass_alpha(double TR, double time_diff_ms) {
 	double freq = sample_freq(time_diff_ms);
 	return (freq * TR / 5.0) / (1.0 + freq * TR / 5.0);
 }
 
-// Initializes the low-pass filter by calculating and storing the alpha value based on the given
-// response time.
+/**
+ * @brief Initializes the low-pass filter by calculating and storing the alpha value
+ *
+ * This function calculates the alpha value based on the given response time and stores
+ * it in the provided pointer. The alpha value is used in subsequent filter updates.
+ *
+ * @param alpha Pointer to store the calculated alpha value
+ * @param response_time Response time constant in milliseconds (must be > 0)
+ * @return w_status_t Returns W_SUCCESS on success, W_INVALID_PARAM if alpha is NULL or
+ * response_time is invalid
+ */
 w_status_t low_pass_filter_init(double *alpha, double response_time);
 
-// Updates the low-pass filter with a new value and returns the operation status
+/**
+ * @brief Updates the low-pass filter with a new value and returns the operation status
+ *
+ * This function applies the low-pass filter algorithm to the new input value using the
+ * provided alpha value. The filtered result is stored in low_pass_value and updated
+ * in-place for the next iteration.
+ *
+ * @param alpha Alpha value (0.0 to 1.0) for the low-pass filter
+ * @param new_input_value New input value to filter
+ * @param low_pass_value Pointer to the current filtered value (updated in-place)
+ * @return w_status_t Returns W_SUCCESS on success, W_INVALID_PARAM if low_pass_value is
+ * NULL or alpha is out of valid range (0.0 to 1.0)
+ */
 w_status_t update_low_pass(double alpha, uint16_t new_input_value, double *low_pass_value);
 
 #ifdef __cplusplus