Speed up screen redraws with a BeagleBone Black and Adafruit TFT via Matthew McMillan
In a previous post I wrote about experimenting with the BeagleBone Black and an Adafruit 2.2″ TFT screen. The TFT screen communicates over SPI using a userspace library. Being a userspace library it is expected it will be slower than driver that is compiled into the kernel but something in the code seemed to be causing redraws to be unnecessarily slow.
To measure how long the screen draws were taking I modified the example image.py script to read the time right before and right after the screen draw function call. I also wrapped a while loop around it so it would redraw the screen repeatedly to give me an average of how long it took.
Depending on how much of the screen was being redrawn and the load on the BBB it would take between 0.7 seconds to 0.9 seconds to execute the disp.display(image) function.
One of the commenters on my previous post tracked down the slowness to one specific function named ‘image_to_data’ in the file ILI9341.py. He also supplied a modification that reduced his screen redraw time dramatically by using NumPy. I tried it out and it reduced my screen redraw times dramatically. Screen redraws went from 0.85 seconds to 0.17 seconds. That is an 80% improvement!
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