A write strobe is used for each byte
(*_tkeep(3:0)
) in the data bus (Four write strobes in our case). Null
strobes are not allowed in the middle of a transfer, or at the end of a transfer. This means
that the word transferred and every additional word up until the last must contain a valid
32-bit value. The last word might be sparse which means it might contain 4, 3, 2, or 1 valid
bytes aligned to the right and the write strobes are used to indicate which bytes are valid.
*_tlast
is used to indicate the last data of a frame. In some cases, the
write strobe signals can be tied to the active state (1) (see Transmit AXI4-Stream Interface).