Is my code too intensive on the cpu?

Question

I am currently building a remote controlled car with the RPi model A+. I am using pygame to run a continuous loop to check the states of the desired keys on the keyboard(w,a,s,d) and based on that run different functions. That cause the RC car to move in the respective direction. The problem I am having is that, the cpu reaches 100% load, and then it freezes(this happened while at stock, and with a medium overclock). I am running both an ssh server and an x11vnc server to control the RPi. Soon after it freezes, it closes both the vnc connection and the ssh connection to the client(the computer I'm using to control the pi). Is all this too much for the Pi to handle? This is my code for the car:

import pygame
import RCcarFunctions
RCcarFunctions.init()
global forward, reverse, left, right
forward, reverse, left, right = False, False, False, False
pygame.init()
pygame.display.init()
size = (640,480)
pygame.display.set_mode((size))
pygame.key.set_repeat(500,10)
print ("Succesfully initialized")
try:
  while True:
    keypressed = pygame.key.get_pressed()
    for event in pygame.event.get():
      if event.type == pygame.KEYDOWN:
        if keypressed[pygame.K_w]:
          forward = True
        if keypressed[pygame.K_a]:
          left = True
        if keypressed[pygame.K_s]:
          reverse = True
        if keypressed[pygame.K_d]:
          right = True
      elif event.type == pygame.KEYUP:
        if event.key == pygame.K_w:
          forward = False
        elif event.key == pygame.K_a:
          left = False
        elif event.key == pygame.K_s:
          reverse = False
        elif event.key == pygame.K_d:
          right = False
      elif event.type == pygame.QUIT:
        RCcarFunctions.cleanup()
        pygame.quit()
    if forward & right:
      RCcarFunctions.right()
    elif forward & left:
      RCcarFunctions.left()
    elif left:
      RCcarFunctions.left()
    elif right:
      RCcarFunctions.right()
    elif forward:
      RCcarFunctions.forward()
      RCcarFunctions.straight()
    elif reverse:
      RCcarFunctions.reverse()
      RCcarFunctions.straight()
    else:
      RCcarFunctions.brake()
except KeyboardInterrupt:
  print ("\ncleaning up")
  RCcarFunctions.cleanup()
  pygame.quit()

If needed the RCcarFunctions library can be found here.

Answer 1

What CPU utilisation do you expect when the code is in a continuous loop? I expect 100%, anything less and there is something wrong.

Is there any reason

    if keypressed[pygame.K_w]:
      forward = True
    if keypressed[pygame.K_a]:
      left = True
    if keypressed[pygame.K_s]:
      reverse = True
    if keypressed[pygame.K_d]:
      right = True

can't be changed to

    if keypressed[pygame.K_w]:
      forward = True
    elif keypressed[pygame.K_a]:
      left = True
    elif keypressed[pygame.K_s]:
      reverse = True
    elif keypressed[pygame.K_d]:
      right = True

The crash is probably because Python never gets a chance to garbage collect and runs out of memory.

Add a time.sleep(0.05) or similar in your while True loop so that garbage collection gets a chance to run.

Answer 2

I'm assuming you have an RPi 1 (single core processor). Your code is far too intensive for any single core machine, and is terribly inefficient (but may sorta work) on a multicore machine. The problem lies in the logic of your code. You are using what's called "polling". Essentially, you're the kid that's constantly asking, "Are we there yet? Are we there yet, Are we there yet!?".

Polling isn't necessarily a bad thing; it's how USB keyboards work. Most usb keyboards poll at 100MHz (iirc). So if you add a short sleep to the loop, you can use this idea and consume far less resources.

Pygame supports an event based solution which essentially allows your program to "block" (sit and do nothing) until an event (like a keypress) is raised. If you're interested in that method, I would suggest you start with their tutorial on how to handle that.

Answer 3

I have tried various different delay, all of which still cause my RPi to crash. So, I connected a different battery source to the RPi(earlier I had one for the motors and the pi now I have one each), and I have come to the conclusion that the RPi wasn't getting enough power. Could this be due to the greater potential difference than supplied? Or is it just lack of current?