problem with LCD Refreshing rate

As Cris72 said - you can also do that into your own Avalon slave.

You do need to write one - it isn't hard, and the 'PIO' slave won't really give you the flexibility you need.

You also need ensure your slave defines all 32 data bits - even if you ignore the high ones.

If you set a C pointer to IO, remember to set bit31 so that the data cache (if used) is bypassed.

One 'cheat' method I've sometimes used to determine which parts of a system are taking the time, is to do some parts twice. If it makes no difference it isn;t the problem!