Vehicle Speed Pulse Period, Frequency, and Vehicle Speed

/* Number of pulses per unit time [usec] */
pulse_cnt_per_usec = 1 / pulse_period_usec;

/* Number of pulses per unit time [usec] = Frequency [Hz] */
pulse_cnt_per_sec = pulse_cnt_per_usec * 1000 * 1000;
pulse_freq = pulse_cnt_per_sec;

/* Number of pulses per unit time [min] */
pulse_cnt_per_min = pulse_cnt_per_sec * 60;

/* Axle rotation speed */
axle_rpm = pulse_cnt_per_min / (number of pulses per axle revolution);

/* JIS D5601 Automotive Speedometer Standard */
/* 637 rpm -> 60 km/h */
/* Kilometers per hour per 1 rpm = 60 / 637 */
speed_kph_per_rpm = 60 / 637;

/* Vehicle speed */
speed_kph = speed_kph_per_rpm * axle_rpm;