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!
Each Tuesday is BeagleBone Black Day here Adafruit! What is the BeagleBone? The BeagleBones are a line of affordable single-board Linux computers (SBCs) created by Texas Instruments. New to the Bone? Grab one of our Adafruit BeagleBone Black Starter Packs and check out our extensive resources available on the Adafruit Learning System including a guide to setting up the Adafruit BeagleBone IO Python Library. We have a number of Bone accessories including add-on shields (called “capes”) and USB devices to help you do even more with your SBC. Need a nice display to go along with your Bone? Check out our fine selection of HDMI displays, we’ve tested all of them with the Beagle Bone Black!