RP2040 does not work with ILI9225

[Bodmer]

The RP2040 does not drive the ILI9225 based displays reliably. This has been traced to the ability of the RP2040 to output SPI data values with minimal gaps between bytes/words. The ILI9225 accepts high SPI rates but empirical evidence shows it requires a significant gap between command bytes and any 16 bit data values.

[Bodmer]

I have the ILI9225 working reliably with the RP2040. I had to use the slow Arduino SPI calls for command register accesses to get it working. Fortunately pixel data can still be sent with a minimal time gap between colour data words, so the graphics tests still return reasonable figures at 32.25MHz SPI clock rate:

Benchmark,                Time (microseconds)
Screen fill (5 times),    109278  (45.75 fps)
Text,                     41025
Lines,                    172236
Horiz/Vert Lines,         11329
Rectangles (outline),     9043
Rectangles (filled),      180311
Circles (filled),         79440
Circles (outline),        63072
Triangles (outline),      50598
Triangles (filled),       104209
Rounded rects (outline),  32442
Rounded rects (filled),   199246
Total = 1052229us
Total = 1.0522s

I will push the updates in the next week or so after more testing.