Function PCD8544.pixel is four times slower than the old Adafruit-Nokia-LCD

[RigacciOrg]

I rewrote an old Python script that is running on the Raspberry Pi model B attached to a Nokia 5110-3310 LCD screen.
The refactoring required the switching from Python2 to Python3 and switching from the old Adafruit_Nokia_LCD library to the new Adafruit_CircuitPython_PCD8544 one. Now I get a severe performance problem with very high CPU load: the old system was running with a load average of 0.20, the new system is running with a load average of 0.90.

Using the yappi Python profiler I recorded the time spent in each funcion call; it turned out that the most time consuming is
PCD8544.image calling PCD8544.pixel.

Do you think that the Adafruit_CircuitPython_PCD8544 is suitable for the old Raspberry Pi model B? I need an LCD image refresh > 1 Hz, because I want to display a clock (including seconds), plus some other data varying at the same rate.

Should I stay with the old Adafruit-Nokia-LCD library? Is it compatibile with Python 3.9?

The system differences are:

• Old system

  • Raspbian based on Debian 8.0
  • Linux Kernel 4.9.35
  • Python 2.7.9
  • Python libraries:
    • Adafruit-Nokia-LCD (0.2.0)
    • Adafruit-PureIO (0.2.1)
    • Adafruit-GPIO (1.0.4)
    • RPi.GPIO (0.6.3)

• New system

  • Raspbian based on Debian 11.2
  • Linux Kernel 5.10.63
  • Python 3.9.2
  • Python libraries:
    • adafruit-circuitpython-pcd8544 (1.2.6)
    • adafruit-circuitpython-busdevice (5.1.1)
    • adafruit-circuitpython-framebuf (1.4.8)
    • Adafruit-PureIO (1.1.9)
    • RPi.GPIO (0.7.0)