TX FIFO status
| USED | Number of entries in the TX FIFO. The field value is in the range [0, 256]. |
| RD_PTR | TX FIFO read pointer: FIFO location from which a data frame is read by the hardware.This field is used only for debugging purposes. |
| WR_PTR | TX FIFO write pointer: FIFO location at which a new data frame is written by the host. This field is used only for debugging purposes. |