gmacgrp_mac_configuration

Reserved

IEEE 802.3as Support for 2K Packets 

When set, the MAC considers all frames, with up to 2,000 bytes length, as normal packets.
When Bit 20 (JE) is not set, the MAC considers all received frames of size more than 2K bytes as Giant frames. When this bit is reset and Bit 20 (JE) is not set, the MAC considers all received frames of size more than 1,518 bytes (1,522 bytes for tagged) as Giant frames. When Bit 20 is set, setting this bit has no effect on Giant Frame status.

SMII Force Transmit Error

When set, this bit indicates to the PHY to force a transmit error in the SMII frame being transmitted.

CRC Stripping for Type Frames

When this bit is set, the last 4 bytes (FCS) of all frames of Ether type (Length/Type field greater than or equal to 1,536) are stripped and dropped before forwarding the frame to the application. This function is not valid when the IP Checksum Engine (Type 1) is enabled in the MAC receiver. This function is valid when Type 2 Checksum Offload Engine is enabled.

Transmit Configuration in RGMII, SGMII, or SMII

When set, this bit enables the transmission of duplex mode, link speed, and link up or down information to the PHY in the RGMII, SMII, or SGMII port. When this bit is reset, no such information is driven to the PHY. 

Watchdog Disable

When this bit is set, the MAC disables the watchdog timer on the receiver. The MAC can receive frames of up to 16,384 bytes. 
When this bit is reset, the MAC does not allow a receive frame which more than 2,048 bytes (10,240 if JE is set high) or the value programmed in Register 55 (Watchdog Timeout Register).

The MAC cuts off any bytes received after the watchdog limit number of bytes.

Jabber Disable

When this bit is set, the MAC disables the jabber timer on the transmitter. The MAC can transfer frames of up to 16,384 bytes.
When this bit is reset, the MAC cuts off the transmitter if the application sends out more than 2,048 bytes of data (10,240 if JE is set high) during transmission.

Frame Burst Enable

When this bit is set, the MAC allows frame bursting during transmission in the GMII half-duplex mode. This bit is reserved (and RO) in the 10/100 Mbps only or full-duplex-only configurations.

Jumbo Frame Enable

When this bit is set, the MAC allows Jumbo frames of 9,018 bytes (9,022 bytes for VLAN tagged frames) without reporting a giant frame error in the receive frame status.

Inter-Frame Gap

These bits control the minimum IFG between frames during transmission.
 * 000: 96 bit times
 * 001: 88 bit times
 * 010: 80 bit times
 * ...
 * 111: 40 bit times
In the half-duplex mode, the minimum IFG can be configured only for 64 bit times (IFG = 100). Lower values are not considered. In the 1000-Mbps mode, the minimum IFG supported is 64 bit times (and above). 

Disable Carrier Sense During Transmission

When set high, this bit makes the MAC transmitter ignore the (G)MII CRS signal during frame transmission in the half-duplex mode. This request results in no errors generated because of Loss of Carrier or No Carrier during such transmission. When this bit is low, the MAC transmitter generates such errors because of Carrier Sense and can even abort the transmissions. 

This bit is reserved (and RO) in the full-duplex-only configurations.

Port Select

This bit selects the Ethernet line speed:
 * 0: For 1000 Mbps operations
 * 1: For 10 or 100 Mbps operations
 
In 10 or 100 Mbps operations, this bit, along with FES bit, selects the exact line speed. In the 10 or 100 Mbps-only (always 1) or 1000 Mbps-only (always 0) configurations, this bit is read-only with the appropriate value. In default 10, 100, or 1000 Mbps configuration, this bit is R_W. The mac_portselect_o signal reflects the value of this bit.

Speed

This bit selects the speed in the MII, RMII, SMII, RGMII, SGMII, or RevMII interface
 * 0: 10 Mbps
 * 1: 100 Mbps
This bit is reserved (RO) by default and is enabled only when the parameter SPEED_SELECT = Enabled. This bit generates link speed encoding when Bit 24 (TC) is set in the RGMII, SMII, or SGMII mode. This bit is always enabled for RGMII, SGMII, SMII, or RevMII interface.
In configurations with RGMII, SGMII, SMII, or RevMII interface, this bit is driven as an output signal (mac_speed_o[0]) to reflect the value of this bit in the mac_speed_o signal. In configurations with RMII, MII, or GMII interface, you can optionally drive this bit as an output signal (mac_speed_o[0]) to reflect its value in the mac_speed_o signal.

Disable Receive Own

When this bit is set, the MAC disables the reception of frames when the phy_txen_o is asserted in the half-duplex mode. 
When this bit is reset, the MAC receives all packets that are given by the PHY while transmitting.
This bit is not applicable if the MAC is operating in the full-duplex mode. This bit is reserved (RO with default value) if the MAC is configured for the full-duplex-only operation.

Loopback Mode

When this bit is set, the MAC operates in the loopback mode at GMII or MII. The (G)MII Receive clock input (clk_rx_i) is required for the loopback to work properly, because the Transmit clock is not looped-back internally.

Duplex Mode

When this bit is set, the MAC operates in the full-duplex mode where it can transmit and receive simultaneously. This bit is RO with default value of 1'b1 in the full-duplex-only configuration.

Checksum Offload

When this bit is set, the MAC calculates the 16-bit one's complement of the one's complement sum of all received Ethernet frame payloads. It also checks whether the IPv4 Header checksum (assumed to be bytes 2526 or 2930 (VLAN-tagged) of the received Ethernet frame) is correct for the received frame and gives the status in the receive status word. The MAC also appends the 16-bit checksum calculated for the IP header datagram payload (bytes after the IPv4 header) and appends it to the Ethernet frame transferred to the application (when Type 2 COE is deselected).

When this bit is reset, this function is disabled. 

When Type 2 COE is selected, this bit, when set, enables the IPv4 header checksum checking and IPv4 or IPv6 TCP, UDP, or ICMP payload checksum checking. When this bit is reset, the COE function in the receiver is disabled and the corresponding PCE and IP HCE status bits are always cleared.

Disable Retry

When this bit is set, the MAC attempts only one transmission. When a collision occurs on the GMII or MII interface, the MAC ignores the current frame transmission and reports a Frame Abort with excessive collision error in the transmit frame status. 

When this bit is reset, the MAC attempts retries based on the settings of the BL field (Bits [6:5]). This bit is applicable only in the half-duplex mode and is reserved (RO with default value) in the full-duplex-only configuration.

Link Up or Down

This bit indicates whether the link is up or down during the transmission of configuration in the RGMII, SGMII, or SMII interface:
 * 0: Link Down
 * 1: Link Up

Automatic Pad or CRC Stripping

When this bit is set, the MAC strips the Pad or FCS field on the incoming frames only if the value of the length field is less than 1,536 bytes. All received frames with length field greater than or equal to 1,536 bytes are passed to the application without stripping the Pad or FCS field. 

When this bit is reset, the MAC passes all incoming frames, without modifying them, to the Host.

Back-Off Limit

The Back-Off limit determines the random integer number (r) of slot time delays (4,096 bit times for 1000 Mbps and 512 bit times for 10/100 Mbps) for which the MAC waits before rescheduling a transmission attempt during retries after a collision. This bit is applicable only in the half-duplex mode and is reserved (RO) in the full-duplex-only configuration.
 * 00: k = min (n, 10)
 * 01: k = min (n, 8)
 * 10: k = min (n, 4)
 * 11: k = min (n, 1)
 
where <i> n </i> = retransmission attempt. The random integer <i> r </i> takes the value in the
range 0 <= r < kth power of 2

Deferral Check

When this bit is set, the deferral check function is enabled in the MAC. The MAC issues a Frame Abort status, along with the excessive deferral error bit set in the transmit frame status, when the transmit state machine is deferred for more than 24,288 bit times in the 10 or 100 Mbps mode.

If the MAC is configured for 1000 Mbps operation or if the Jumbo frame mode is enabled in the 10 or 100 Mbps mode, the threshold for deferral is 155,680 bits times. Deferral begins when the transmitter is ready to transmit, but it is prevented because of an active carrier sense signal (CRS) on GMII or MII. 

The defer time is not cumulative. For example, if the transmitter defers for 10,000 bit times because the CRS signal is active and then the CRS signal becomes inactive, the transmitter transmits and collision happens. Because of collision, the transmitter needs to back off and then defer again after back off completion. In such a scenario, the deferral timer is reset to 0 and it is restarted.
When this bit is reset, the deferral check function is disabled and the MAC defers until the CRS signal goes inactive. This bit is applicable only in the half-duplex mode and is reserved (RO) in the full-duplex-only configuration.

Transmitter Enable

When this bit is set, the transmit state machine of the MAC is enabled for transmission on the GMII or MII. When this bit is reset, the MAC transmit state machine is disabled after the completion of the transmission of the current frame, and does not transmit any further frames.

Receiver Enable

When this bit is set, the receiver state machine of the MAC is enabled for receiving frames from the GMII or MII. When this bit is reset, the MAC receive state machine is disabled after the completion of the reception of the current frame, and does not receive any further frames from the GMII or MII.

Preamble Length for Transmit Frames

These bits control the number of preamble bytes that are added to the beginning of every Transmit frame. The preamble reduction occurs only when the MAC is operating in the full-duplex mode.
 * 2'b00: 7 bytes of preamble
 * 2'b01: 5 byte of preamble
 * 2'b10: 3 bytes of preamble
 * 2'b11: 1 byte of preamble