Full Duplex Flow Control - Freescale Semiconductor MCF54455 Reference Manual

Fast Ethernet Controllers (FEC0 and FEC1)
Table 26-38. Destination Address to 6-Bit Hash (continued)

26.5.11 Full Duplex Flow Control

Full-duplex flow control allows you to transmit pause frames and to detect received pause frames. Upon
detection of a pause frame, MAC data frame transmission stops for a given pause duration.
To enable PAUSE frame detection, the FEC must operate in full-duplex mode (TCRn[FDEN] set) with
flow control (RCRn[FCE] set). The FEC detects a pause frame when the fields of the incoming frame
match the pause frame specifications, as shown in
with the frame should indicate that the frame is valid.
48-bit Destination Address
48-bit Source Address
16-bit PAUSE Duration
The receiver and microcontroller modules perform PAUSE frame detection. The microcontroller runs an
address recognition subroutine to detect the specified pause frame destination address, while the receiver
detects the type and opcode pause frame fields. On detection of a pause frame, TCRn[GTS] is set by the
FEC internally. When transmission has paused, the EIRn[GRA] interrupt is asserted and the pause timer
begins to increment. The pause timer uses the transmit backoff timer hardware for tracking the appropriate
collision backoff time in half-duplex mode. The pause timer increments once every slot time, until
OPDn[PAUSE_DUR] slot times have expired. On OPDn[PAUSE_DUR] expiration, TCRn[GTS] is
cleared allowing MAC data frame transmission to resume. The receive flow control pause status bit
(TCRn[RFC_PAUSE]) is set while the transmitter pauses due to reception of a pause frame.
To transmit a pause frame, the FEC must operate in full-duplex mode and you must set flow control pause
(TCRn[TFC_PAUSE]). After TCRn[TFC_PAUSE] is set, the transmitter sets TCRn[GTS] internally.
When the transmission of data frames stops, the EIRn[GRA] (graceful stop complete) interrupt asserts and
the pause frame is transmitted. TCRn[TFC_PAUSE,GTS] are then cleared internally.
You must specify the desired pause duration in the OPDn register.
26-45
6-bit Hash
48-bit DA
(in hex)
FDFF_FFFF_FFFF
DDFF_FFFF_FFFF
9DFF_FFFF_FFFF
BDFF_FFFF_FFFF
Table
Table 26-39. PAUSE Frame Field Specification
0x0180_C200_0001 or Physical Address
16-bit Type
16-bit Opcode
Hash Decimal
Value
0x3C 60
0x3D 61
0x3E 62
0x3F 63
26-39. In addition, the receive status associated
Any
0x8808
0x0001
0x0000 – 0xFFFF
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