I'm using an ILI9341-based LCD module, and the 4-wire SPI interface to communicate with it. According to the datasheet's spec for this interface, I should be able to write at up to 1s/100ns(twc)=10Mhz, and read at up to 1s/150ns(trc)=6.66Mhz.
However, I am successfully writing and reading at 24Mhz! Not just for a simple test case, either. I'm doing complex graphics, mixed reads/writes for alpha blends, both 16-bit and 24-bit pixel writes, and so on - yet haven't seen a single glitch. (Except those caused when I bump my dodgy old breadboard or jumper wires. That I'm using such poor connections, and it's still working at this speed when not physically disturbed, make this even more amazing. The signal integrity must be horrible.)
In the past I've tried communicating with other complex SPI devices at speeds past their ratings, just to see what would happen. All started showing issues with modest increases, even when run at max Vdd.
Yet I'm reading from this at 360% of its max rated speed! And I know of cases of others doing the same with their ILI9341-based LCD, as well.
All of which really makes me question whether I've read the spec and converted from ns to Mhz properly. Did I simply make a stupid mistake? Here's the relevant page from the datasheet:
