Spartan 3A IOBUFT时序约束错误

您好......我正在使用IOBUF在Spartan 3A中实现双向数据总线。
IOBUF MEM0DO（.O（xmem_data_in [0]）,. IO（xmem_data [0]）,. I（xmem_data_out [0]）,. T（xmem_dir））;
我的时钟有一个通用的时序约束：
NET“clk200M”TNM_NET = clk200M; tiMESPEC TS_clk200M = PERIOD“clk200M”5 ns;
我得到一个不可能映射的错误，它告诉我从输出缓冲器到焊盘并返回通过输入缓冲器的时间和可调延迟到单独实例化的输入锁存器相对于三态控制信号太长。
纯粹由于逻辑原因，它太长了。
这停止了​​它的轨道实施。
所有信号都由同一时钟产生。
我不关心这条路径，因为我要么写出这个引脚，要么从这个引脚读取。
我从不想读我写的东西。
有谁知道如何解决这个问题？
我能以不同的方式约束它吗？
这种可调延迟有助于吗？
从我所看到它默认为0.我可能没有这么好描述...... :(



以下为原文

Hello...I am implementing a bi directional data bus in a Spartan 3A using an IOBUF.

    IOBUF MEM0DO(.O(xmem_data_in[0]), .IO(xmem_data[0]), .I(xmem_data_out[0]), .T(xmem_dir));

I have a generic timing constrain for my clock:

NET "clk200M" TNM_NET = clk200M;
TIMESPEC TS_clk200M = PERIOD "clk200M" 5 ns;

I am getting an impossible to map error which tells me that the time from the output buffer to the pad and back through the input buffer and the adjustable delay to a seperately instantiated input latch is too long versus the tri state control signal.  It is too long purely due to logic.  Which stops the implementation in it's tracks.  All signals are generated by the same clock.

I don't care about this path since I am either writing out of this pin or reading from this pin.  I never want to read what I am writing.

Anyone know how to work around this?  Can I constrain it differently?  Does this adjustable delay contribute?  From what I have seen it defaults to 0.  I may not have described this well...:(