Full-Duplex Pause Operations - Samsung S3C2500B User Manual

ETHERNET CONTROLLER

7.5.3 FULL-DUPLEX PAUSE OPERATIONS

Flow control can be done by the use of control frames. The receive logic in the flow control block recognise a
MAC control frame as follows:
— The current specification for full-duplex flow control specifies a special destination address for the Pause
operation frame. In order for the MAC to receive frames that contain this special destination address, the
address must be programmed in one of the CAM entries. This CAM entry must then be enabled, and the
CAM activated. Some CAM entries are also used when generating a flow control frame using the MSdPause
bit in the MACTXCON register.
— The length/type field is a 2-octet field that shall contain the hexadecimal value: 88-08. The frame length must
be at least 64 bytes, including CRC. The CRC must be valid, and the frame must contain a valid pause
opcode and a parameter (pause period) field. If the length/type field does not have the special value
specified for MAC control frames, the MAC takes no action, and the frame is treated as a normal frame. If
the frame is marked as a MAC control frame and pass-through is enabled, it is passed to the software
drivers.
User can set the control bit in the MAC control register to generate a Full-Duplex pause operation or other MAC
control functions, even if the transmitter itself is paused.
The command and status registers initiate the sending of a MAC control frame, enable and disable MAC control
functions, and read the values of the flow control counters.
(minFrameSize-160)/8
Octets
7-46
6 Octets
6 Octets
2 Octets
2 Octets
MAC Control Opcode
MAC Control Parameters
Reserved (Transmitted as Zeroes)
LSB
b0
Frame Transmitted
Figure 7-12. MAC Control Frame Format
Destination
Address
Source
Address
Length/Type
b7
Bits within
Left-to-Right
Octers within
Frame Transmitted
Top-to-Bottom
MSB
S3C2500B