graph.py

servo_hz = 1000.

def compute(freq):
    fsys = 125000000
    #divisor = 128
    if freq < 100:
        divisor = (1<<16)-1
    elif freq < 200:
        divisor = (1<<15)-1
    else:
        divisor = int(fsys / (freq * (15 + 1)))
        if divisor >= 1<<16:
            raise ValueError(f"Frequency too low for servo {freq} divisor {divisor}")
    delay = (fsys // divisor) / freq - 15
    if delay < 1: delay = 1
    delay = int(delay) /16.

    period = 1./(fsys // divisor) * (15 + delay)
    true_freq =  1./period 
    rel_error = (true_freq - freq) / freq
    return (rel_error), period, delay
    
freqs = []
err = []
delays  = []
delay_counts = []
minfreq, maxfreq = 1, 1000
for freq in range(minfreq, maxfreq):
    e = compute(freq)
    freqs.append(freq)
    err.append(e[0])
    delays.append(e[1])
    delay_counts.append(e[2])

import matplotlib.pyplot as plt
plt.subplot(3,1,1)
plt.plot(freqs, delays, '-', [minfreq, maxfreq], [1./servo_hz, 1./servo_hz],'-')
plt.subplot(3,1,2)
plt.plot(freqs, err)
plt.subplot(3,1,3)
plt.plot(freqs, delay_counts)
print(freqs, err)
plt.show()