How to set gpmc_timing for st16C554?

Hi,

I drive a st16c554 with am335x gpmc port. But I'm stuck at the gpmc_timing.

I set the gpmc at 8bit non-multimux asynchronous nor flash mode. Is this correct?

now my problem is the st16c554 can't be detected.  I suspect the gpmc_timing is not correct.

and I'm puzzled by the timing diagram ( I found it in the SPRS717D document figure 5-18):

all the timing is based on CS_ON point except DATA signal. but what the time gap between start of FA5 and CS_ON?

I need that value to set DATA signal timing based on CS_ON.

And another question:

How to set DATA hold time? below is the timing chart for st16c554:

beside DATA hold time T16h, I don't know how to set T15d use the formula provided in sprs figure 5-18.

Thank you very much.