6437 GPIO timing

ephraim oved said:

The SYSCLK3 runs at 99 Mhz.

Writing to a GPIO output takes about 11 nSec.

Reading from the GPIO input takes about 55 nSec.

This sounds about right. The CPU cannot go faster than 1 clock cycle to write to the SET_DATA register, so after it writes to the register the CPU is "done" with the GPIO write; however, this is different for reads because the CPU is not "done" until it has actually read the data back via the IN_DATA register. The GPIO has inherent latencies between register accesses and GPIO toggles. Because the GPIO module is operating slower than the CPU (SYSCLK3 vs. SYSCLK1) I would assume this is where the additional delay is coming into play.