We designed a custom board similar to ATSAME70-XPLD with ATSAME70Q21A microcontroller. There is also SDRAM chip IS42S16800F-5TLI there.
The problem is that SDRAM doesn't work when I set Fmck higher than 180 MHz. while the SDRAM on the ATSAME70-XPLD board works perfectly with the frequency 300 MHz.
What can be the reason of it? Is it a hardware issue (like bad layout, unmatched lines etc.) or a software one (wrong configuration)?