Fast I/O registers in Bidirection IO

[Altera_Forum]

Hi, I am trying to improve the IO timing by using fast IO registers. 

However, how could I set a proper register when facing a bidirection IO?  Thank you~!

[Altera_Forum]

You have three settings at your disposal: 

FAST_INPUT_REGISTER FAST_OUTPUT_REGISTER FAST_OUTPUT_ENABLE_REGISTER  For a bidirectional IO, you can set any or all of these to TRUE for the pin in question. Your design must of course actually support the function: 1 - The pin must be driven directly by a register output with no combinatorial logic. 2 - The input must be fed directly to a register with no combinatorial logic 3 - If you choose to use a fast output enable then the output enable for the pin must be driven directly by a register.  Jake

[Altera_Forum]

--- Quote Start ---    For a bidirectional IO, you can set any or all of these to TRUE for the pin in question. Your design must of course actually support the function: 1 - The pin must be driven directly by a register output with no combinatorial logic. 2 - The input must be fed directly to a register with no combinatorial logic 3 - If you choose to use a fast output enable then the output enable for the pin must be driven directly by a register.   --- Quote End ---    Thank you for your rapidly reply!  When using a bidirection IO, the output and input are not directly fed by a register, but via a buffer. Even if my output reg before bidirection buffer is register pipelined so that there is certainly no combinatorial logic. I think course 1 and 2 are not met because of the buffer itself. Only the buffer's enable reg could be set in this condition?  thank you ag~

[Altera_Forum]

I should be more clear. Besides the buffer ... there can be nothing between the pin and register. 

 Jake

[Altera_Forum]

--- Quote Start ---  I should be more clear. Besides the buffer ... there can be nothing between the pin and register.  Jake  --- Quote End ---     I think I've been thinking too much to waht you've said just now, hehe~ And so according to this, I just set and apply the Fast IO register constrains directly to the Bidir IO pin, it will do work.  Thank you very much!