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Ethernet (ETH): media access control (MAC) with DMA controller
Bit 0 FCB/BPA: Flow control busy/back pressure activate
This bit initiates a Pause Control frame in Full-duplex mode and activates the back pressure
function in Half-duplex mode if TFCE bit is set.
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 continues to be set to signify that a frame transmission is in progress.
After completion of the Pause control frame transmission, the MAC resets 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 TFCE is set), back pressure is asserted by the
MAC core. During back pressure, when the MAC receives a new frame, the transmitter starts
sending a JAM pattern resulting in a collision. When the MAC is configured to Full-duplex
mode, the BPA is automatically disabled.
Ethernet MAC VLAN tag register (ETH_MACVLANTR)
Address offset: 0x001C
Reset value: 0x0000 0000
The VLAN tag register contains the IEEE 802.1Q VLAN Tag to identify the VLAN frames.
The MAC compares the 13
0x8100, and the following 2 bytes are compared with the VLAN tag; if a match occurs, the
received VLAN bit in the receive frame status is set. The legal length of the frame is
increased from 1518 bytes to 1522 bytes.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
Reserved
Bits 31:17 Reserved
Bit 16 VLANTC: 12-bit VLAN tag comparison
When this bit is set, a 12-bit VLAN identifier, rather than the complete 16-bit VLAN tag, is used
for comparison and filtering. Bits[11:0] of the VLAN tag are compared with the corresponding
field in the received VLAN-tagged frame.
When this bit is reset, all 16 bits of the received VLAN frame's fifteenth and sixteenth bytes are
used for comparison.
Bits 15:0 VLANTI: VLAN tag identifier (for receive frames)
This contains the 802.1Q VLAN tag to identify VLAN frames, and is compared to the fifteenth
and sixteenth bytes of the frames being received for VLAN frames. Bits[15:13] are the user
priority, Bit[12] is the canonical format indicator (CFI) and bits[11:0] are the VLAN tag's VLAN
identifier (VID) field. When the VLANTC bit is set, only the VID (bits[11:0]) is used for
comparison.
If VLANTI (VLANTI[11:0] if VLANTC is set) is all zeros, the MAC does not check the fifteenth
and sixteenth bytes for VLAN tag comparison, and declares all frames with a Type field value
of 0x8100 as VLAN frames.
1010/1096
th
th
and 14
bytes of the receiving frame (Length/Type) with
rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw
Doc ID 13902 Rev 12
9
8
7
6
5
4
3
VLANTI
RM0008
2
1
0
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