The internalFIFO depth (INTERNAL_WFIFO_DEPTH) and MEM_LATENCY generics are maintained by the Vivado HLS synthesis engine. Therefore,users cannot configure them with directives and should not change the value manually. The "-depth" option for the directive is only used by the C-RTL mixed simulation. It controls the depth of the FIFO between C Testbench and the RTL. This option is not used in RTL implementation.