After the interim demo, the biggest area for improvement is the refresh rate of our display. We need every piece to be faster for this to happen, so this week I worked on improving the laser cut chassis and some of the software. The chassis we used for the demo had one hole drilled in manually since I forgot to laser cut it, and at higher speeds, the imperfections in the hole caused our tube to rub against wood creating friction and bad sounding noises. I redesigned the laser cut pieces to actually have this hole so we can hopefully reach higher speeds. I also added some holes to hold it better for transportation and some minor improvements to allow for easier assembly.
On the software side, I noticed during the demo at times the display could seem a bit laggy, which motivated me to do more testing. This is likely either due to networking logic or display driving, so I investigated display logic at first (since we also got our full-sized displays which means more data to be displayed).
I created some tests to measure peak performance in terms of how fast we can update both displays, and I originally measured a maximum of 95 fps, which is too low when we are spinning at high speeds. I found that the library we used, rpi-rgb-led-matrix, used a somewhat slow implementation for using pwm to drive the display. To fix this, I replaced the library with custom direct memory access (DMA) so there’s less cpu time spent on driving LED outputs. This vastly improved performance to over 7000 fps, and next week I will work on fully testing to make sure this doesn’t affect any other part of the software.
Other verification will eventually include doing network testing to see if our throughput is enough. If not, we might have to look at improving our wifi hardware or wrapping everything in aluminum foil or something.