The receiver tag registers (receive

The receiver tag registers (receiver frame tag and user data (RX_FRAME_TAG_UDATA) register and receiver ping tag (RX_PING_TAG) register) have the Least Significant Bit is set to 0. The actual received tag is in the bit positions 4:1. The reason for this is to facilitate user software to create a table of functions which can be called depending on the tag value. A function pointer needs a 32-bit storage space and hence each successive pointer will be offset by 2. If the first pointer is at address x, then the second pointer will be at address x+2, the third at address x+4 and so on. By keeping the LSB 0, the five bits of the tag register (bits 4:0) can now be directly used as an index into a table of function pointers.