Flow control register
| FCB | Flow Control Busy/Backpressure Activate This register field can be read by the application (Read), can be set to 1 by the application with a register write of 1 (Write Set), and is cleared to 0 by the core (Self Clear). The application cannot clear this type of field, and a register write of 0 to this bit has no effect on this field. This bit initiates a Pause Control frame in Full-Duplex mode. In Full-Duplex mode, this bit should be read as 0 before writing to the Flow Control register. To initiate a Pause control frame, the Application must set this bit to 1. During a transfer of the Control Frame, this bit will continue to be set to signify that a frame transmission is in progress. After the completion of Pause control frame transmission, the MAC will reset this bit to 0. The Flow Control register should not be written to until this bit is cleared. In Half-Duplex mode, when this bit is set (and TFE is set), then backpressure is asserted by the MAC Core. During backpressure, when the MAC receives a new frame, the transmitter starts sending a JAM pattern resulting in a collision. This control register bit is logically ORed with the flow controller input signal for the backpressure function. When the MAC is configured to Full- Duplex mode, the BPA is automatically disabled. |
| TFE | Transmit Flow Control Enable In Full-Duplex mode, when this bit is set, the MAC enables the flow control operation to transmit Pause frames. When this bit is reset, the flow control operation in the MAC is disabled, and the MAC will not transmit any Pause frames. In Half-Duplex mode, when this bit is set, the MAC enables the back-pressure operation. When this bit is reset, the backpressure feature is disabled. |
| RFE | Receive Flow Control Enable When this bit is set, the MAC will decode the received Pause frame and disable its transmitter for a specified (Pause Time) time. When this bit is reset, the decode function of the Pause frame is disabled. |
| UP | Unicast Pause Frame Detect When this bit is set, the MAC will detect the Pause frames with the station’s unicast address specified in MAC Address0 High Register and MAC Address0 Low Register, in addition to the detecting Pause frames with the unique multicast address. When this bit is reset, the MAC will detect only a Pause frame with the unique multicast address specified in the 802.3x standard. |
| PLT | Pause Low Threshold This field configures the threshold of the PAUSE timer at which the input flow control is checked for automatic retransmission of PAUSE Frame. The threshold values should be always less than the Pause Time configured in Bits[31:16]. For example, if PT = 0x100 (256 slot-times), and PLT = 01, then a second PAUSE frame is automatically transmitted if the flow control signal is asserted at 228 (256 - 28) slot-times after the first PAUSE frame is transmitted. |
| RESERVED | Reserved |
| DZPQ | Disable Zero-Quanta Pause When set, this bit disables the automatic generation of Zero-Quanta Pause Control frames on the deassertion of the flow-control signal from the FIFO layer. When this bit is reset, normal operation with automatic Zero-Quanta Pause Control frame generation is enabled. |
| RESERVED | Reserved |
| PT | Pause time This field holds the value to be used in the Pause Time field in the transmit control frame. If the Pause Time bits is configured to be double-synchronized to the MII clock domain, then consecutive writes to this register should be performed only after at least 4 clock cycles in the destination clock domain. |