Re: Adafruit 2.8 inch TFT screen

I have a 2.8" TFT display connected to a Galileo Gen2. I was initially really discouraged, because the performance of the graphicstest sketch was truly miserable.

I spent the day with this display today, seeing how far I could take graphics performance. Relative to the Intel-tweaked Adafruit_ILI9341 driver, I got between 100-900x speedups, which was heartening. My initial gains were thanks to KurtE's tweaks, mostly reducing the clock divider.

Additionally, I implemented a buffered version of the Adafruit_ILI9341 class, writing to a dynamically allocated framebuffer, and only presenting the buffer at the end of each test. I'm a software guy, so I was seeking the wins where I could get them. This greatly reduced the number of SPI calls, which makes a difference when you're setting a lot of pixels individually. I copy the framebuffer five rows at a time, nearly maxxing out the 4KB transferBuffer limit. If I could bump that up to 160KB, I could reduce the number of SPI calls by another factor of ~40, which might bring us into the realm of real-time rendering.

For posterity, here are the timings I got with my tests today (all in microseconds). Note that the Buffered times are utterly dominated by the transferBuffer calls, which take 90% of the frame time.

The takeaway for me is that Galileo is harshly bandwidth-limited over the SPI interface, but with careful management of calls, you can use this display in applications that don't require real-time responsiveness.