On Wed, 17 Jan 2018, Mark Webb-Johnson wrote:
The only solution we can see is to continue to use GPIO22 for FL_CS2 external flash, but use a level converter 3.3V -> 1.8V. We only need uni-directional, but it must operate fast enough not to interfere with a 40MHz SPI bus. Maybe a resistor voltage divider would be too slow / interfere too much, so safer to use a simple single channel uni-directional 3.3V->1.8V logic level shifter chip.
Just out of curiousity I looked in DigiKey to see what SMD unidirectional level translators were available. They all seem to have typical propagation delays in the neighborhood of 5ns. Since the cycle time for 40MHz is 25ns, it seems like that delay would be a problem. -- Steve