IO主要包括通过数值传递和通过指针(或references\数组)。
对应于"wire"类型，没有握手协议。
Unconditional IO is used most often for either control type interfaces, where the IO does not change, on in designs that are pipelined with II=1 and the IO is read or written every clock cycle.
具体细分如下：
Pass by reference is when a variable is declared as either a pointer or a reference on the design interface. This means that the data that the variable “points to” or “refers to” is stored externally. In other words the “data” is stored off-chip.
Example 5-1. Unconditional IO Passed by Reference