About a year ago I designed a PCB with a processor and RAM (400MHz and 133MHz speed respectively). I did not know about length matching and it did not work properly. I then redesigned the board with length matched traces and it worked.
Now I have 3 questions.
I am designing a PCB with an MCU and there will be JTAG, SPI, I2C and USB. Do they need length matching? (SPI should not need in my perspective but others might need).
Since it is 4 layer would that be a problem if I pass traces below crystals (12MHz and 32.768kHz)? Would that trace affect crystals performance?
I dedicated one layer to power from a Li-Po battery because there will be a huge amount of current draw. But I also need this layer for use with traces of some GPIO pins. Would that create problem?