Optimized oled script startup and shutdown (#573)

* Optimize the oled script for quicker startup. Blank the screen instead of showing a splash.

* Remove shutdown splash bitmap images

* Cleanup

* Resolve pylint warnings

src/oled_monitor/rascsi_oled_monitor.py

@@ -31,8 +31,8 @@
  THE SOFTWARE.
 """
 import argparse
+import sys
 from time import sleep
-from sys import argv
 from collections import deque
 from board import I2C
 from adafruit_ssd1306 import SSD1306_I2C
@@ -95,20 +95,22 @@ I2C = I2C()
 
 # 128x32 display with hardware I2C:
 OLED = SSD1306_I2C(WIDTH, HEIGHT, I2C, addr=0x3C, reset=OLED_RESET)
+OLED.rotation = ROTATION
 
 print("Running with the following display:")
 print(OLED)
 print()
 print("Will update the OLED display every " + str(DELAY_TIME_MS) + "ms (approximately)")
 
-# Clear display.
-OLED.rotation = ROTATION
-OLED.fill(0)
+# Show a startup splash bitmap image before starting the main loop
+# Convert the image to mode '1' for 1-bit color (monochrome)
+# Make sure the splash bitmap image is in the same dir as this script
+IMAGE = Image.open(f"splash_start_{HEIGHT}.bmp").convert("1")
+OLED.image(IMAGE)
 OLED.show()
 
-# Create blank image for drawing.
-# Make sure to create image with mode '1' for 1-bit color.
-IMAGE = Image.new("1", (OLED.width, OLED.height))
+# Keep the pretty splash on screen for a number of seconds
+sleep(4)
 
 # Get drawing object to draw on image.
 DRAW = ImageDraw.Draw(IMAGE)
@@ -138,11 +140,6 @@ LINE_SPACING = 8
 # Some other nice fonts to try: http://www.dafont.com/bitmap.php
 FONT = ImageFont.truetype('type_writer.ttf', FONT_SIZE)
 
-# Load a bitmap image for start and stop splash screens and convert to monocrome
-# Make sure the splash bitmap image is in the same dir as this script
-SPLASH_START = Image.open(f"splash_start_{HEIGHT}.bmp").convert("1")
-SPLASH_STOP = Image.open(f"splash_stop_{HEIGHT}.bmp").convert("1")
-
 IP_ADDR, HOSTNAME = get_ip_and_host()
 
 
@@ -190,28 +187,7 @@ def formatted_output():
     return output
 
 
-def start_splash():
-    """
-    Displays a splash screen for the startup sequence
-    """
-    OLED.image(SPLASH_START)
-    OLED.show()
-    sleep(4)
-
-def stop_splash():
-    """
-    Displays a splash screen for the shutdown sequence
-    """
-    OLED.image(SPLASH_STOP)
-    OLED.show()
-
-# Show a startup splash bitmap image before starting the main loop
-start_splash()
-
 with GracefulInterruptHandler() as handler:
-    """
-    The main loop of displaying attached device info, and other info
-    """
     while True:
 
         # The reference snapshot of attached devices that will be compared against each cycle
@@ -225,10 +201,10 @@ with GracefulInterruptHandler() as handler:
         while snapshot == ref_snapshot:
             # Draw a black filled box to clear the image.
             DRAW.rectangle((0, 0, WIDTH, HEIGHT), outline=0, fill=0)
-            y_pos = TOP
+            Y_POS = TOP
             for output_line in active_output:
-                DRAW.text((X_POS, y_pos), output_line, font=FONT, fill=255)
-                y_pos += LINE_SPACING
+                DRAW.text((X_POS, Y_POS), output_line, font=FONT, fill=255)
+                Y_POS += LINE_SPACING
 
             # Shift the index of the array by one to get a scrolling effect
             if len(active_output) > LINES:
@@ -242,6 +218,8 @@ with GracefulInterruptHandler() as handler:
             snapshot = formatted_output()
 
             if handler.interrupted:
-                # Catch interrupt signals and show a shutdown splash bitmap image
-                stop_splash()
-                exit("Shutting down the OLED display...")
+                # Catch interrupt signals and blank out the screen
+                DRAW.rectangle((0, 0, WIDTH, HEIGHT), outline=0, fill=0)
+                OLED.image(IMAGE)
+                OLED.show()
+                sys.exit("Shutting down the OLED display...")