two io bank can share one IDELAYCTRL instance?
It is true that there is one IDELAYCTRL per bank, and the IDELAY/ODELAY cells in that bank use that IDELAYCTRL.
However, the tools will replicate instantiated IDELAYCTRL cells. The IDELAYCTRL cell takes two inputs (a clock and a reset) and generates one output (locked, that is usually ignored). These signals can be routed anywhere on the die (assuming the clock comes from a BUFG), therefore, they can be connected to the IDELAYCTRL in any bank. When the tool sees a bank that has IDELAY/ODELAY cells instantated and there is one (and only one) IDELAYCTRL instantated in the design, it will connect the clock and reset signal to the IDELAYCTRL cells in each bank that has IDELAY/ODELAY (and AND the locked signals together, I think).
If you need to use different clock, reset and locked signals, you group IDELAY/ODELAY and IDELAYCTRL cells using the property IODELAYGROUP - this tell the tools which IDELAYCTRL needs to be replicated in a given bank. You cannot have two different IODELAYGROUP groups in the same bank (since there is only one IDELAYCTRL).
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