Sundance Spas ST201 - Manual (Page 13)

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Sundance Technology ST201 PRELIMINARY draft 2
dress register. Setting the ReceiveBroadcast and
ReceiveMulticast bits in the ReceiveMode register
will allow the ST201 to receive all broadcast and
multicast frames, respectively. The ReceiveMultic-
astHash bit in ReceiveMode enables a filtering
mechanism for Ethernet multicast frames. This fil-
tering mechanism uses a 64-bit hash table (Hash-
Table register) for selective reception of Ethernet
multicast frames. A CRC algorithm is applied to the
destination address of incoming Ethernet multicast
frames. The least significant 6 bits of the CRC
result are used as an index into the hash table. The
Ethernet multicast frame will be accepted by the
ST201 when the corresponding hash table bit is
set, otherwise the frame will be discarded. The
host system must configure the hash table before
any multicast frames are received using the filter-
ing mechanism.
Additionally, Ethernet frames containing IP multi-
cast destination addresses can also be received by
setting the ReceiveIPMulticast bit in the Receive-
Mode register. IP multicast, or Host Extension for
IP Multicasting, datagrams map to frames with
Ethernet destination addresses of 0x01005e******
(where * represents any hexadecimal value).
The MACCtrl register is used to configure parame-
ters including full duplex, flow control, and statistics
gathering.
The ST201 can operate in either half duplex or full
duplex mode. In half duplex mode, the ST201
implements the CSMA/CD algorithm. CSMA/CD
requires that only one node transmit at a time. If
multiple nodes attempt to transmit simultaneously
(indicated when both the receive and transmit sig-
nals are active) a collision will occur resulting in
frame loss, and typically requiring re-transmission.
In full duplex mode, the ST201 can transmit and
receive frames simultaneously without incurring
collisions. To configure the ST201 for full duplex
mode operation, the host system must detect a full
duplex physical link via the appropriate PHY device
register, and must set the FullDuplexEnable bit in
the MACCtrl register.
The IEEE 802.3x Full Duplex standard defines a
special frame known as the PAUSE MAC Control
frame. The PAUSE frame is used to implement
flow control in full duplex networks allowing sta-
tions on opposite ends of a full duplex link the abil-
ity to inhibit transmission of MAC data frames for a
specified period of time. The PAUSE frame format
is defined as shown in Figure 1.
In Figure 1, bytes within fields are transmitted left
to right, bits within bytes transmitted least-signifi-
cant bit first.
Whenever the FlowControlEnable bit in the MAC-
Ctrl register is set, the ST201 compares the desti-
nation address with 0x0180C2000001 and the type
field with 0x8808 in all incoming frames. If both
fields match, the ST201 further checks for the
PAUSE opcode (0x0001) in the MAC Control
Opcode field. If found, the ST201 inhibits transmis-
sion of all data frames for the time specified in the
two-byte pause_time field. The pause_time field is
specified in slot times relative to the current data
rate; one slot time is 51.2 us at 10 Mbps, and 5.12
us at 100 Mbps. The transmission of PAUSE
frames is the responsibility of the host. The MAC
Control frame must be constructed by the host and
placed into the TxFIFO. The driver should program
the ReceiveMode register to receive PAUSE (MAC
Control frame) when flow control is enabled. For
end station applications, host system should only
accept PAUSE frames, and not generate them.
Flow control is designed to originate from network
devices such as switches.
DA 0x0180C2000001
SA
TYPE
OPCODE
PAUSE TIME
PAD
0x8808
0x0001
6
6
2
2
2
42
FIELD
LENGTH
(BYTES)
FIGURE 1: PAUSE Frame