Raspberry Pi Pico PIO proof of concept, 15M pixels/sec

If anybody is using LVGL with Raspberry Pico, I suggest looking considering the Pico PIO for high throughput interface with the display.

Below is a proof of concept that uses a PIO state machine and 8 bits parallel data path to a ILI9488 TFT controller. The byte rate is 30M/sec which results in 15M pixels/sec (two bytes per pixels).

The proof of concept supports both 8 and 16 bits color depths with on-the-fly 8 bit to 16 bits color mapping to meet the 16 bits requirement of the TFT controller. Using LVGL 8 bits allows to have RAM buffer than contains the entire 320x480 screen, which provides smooth display due to the short display update time.

The PIO uses an 8 entries FIFO, and supports single byte mode for commands and data and dual byte mode for the pixels, as required by the ILI9488. The strobe WR pulses are generated automatically and the state machine is fine tuned for proper setup and hold times.

The hardware FIFO is also supported by the DMA but since the firmware runs fast enough to keep it full, I didn’t bothered with DMA.


Wow, that great!

I’d be very curious how it runs v8’s widget demo with enabled FPS monitor. Would b complicated to try it out?

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I have on my todo list to convert the app to V8 but need to find time. Will update here once it happens.

With a simple fill screen test program, it does 100fps (320x480) but with LVGL we need to add the rendering time.

BTW, would you expect significant different in LVGL in-memory rendering time between 8bit and 16bit color depth? I use 8 bits to fit the entire screen in RAM and map to 16bits on the fly during screen updates which can still send to the screen 30MB/sec.

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Using 8 bit color depth instead of 16 affects the fill rate and “copy” rate but its fast anyway. I’m sure you lose more on converting from 8 to 16 bit even if you use a lookup table. Besides with 8 bit you lose the color gradients and fine antialiasing.