LAN9311 Datasheet, PDF (157/461 Pages) SMSC Corporation – Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

11.2
Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
IEEE 1588 Time Stamp
The LAN9311/LAN9311i contains three identical IEEE 1588 Time Stamp blocks as shown in
Figure 11.1. These blocks are responsible for capturing the source UUID, sequence ID, and current
64-bit IEEE 1588 clock time upon detection of a Sync or Delay_Req message type on their respective
port. The mode of the clock (master or slave) determines which message is detected on receive and
transmit. For slave clock operation, Sync messages are detected on receive and Delay_Req messages
on transmit. For master clock operation, Delay_Req messages are detected on receive and Sync
messages on transmit. Follow_Up, Delay_Resp and Management packet types do not cause capture.
Each port may be individually configured as an IEEE 1588 master or slave clock via the master/slave
bits (M_nS_1 for Port 1, MnS_2 for Port2, and M_nS_MII for Port 0) in the 1588 Configuration Register
(1588_CONFIG). Table 11.1 summarizes the message type detection under slave and master IEEE
1588 clock operation.
Table 11.1 IEEE 1588 Message Type Detection
IEEE 1588 CLOCK MODE
RECEIVE
Slave
(M_nS_x = 0)
Master
(M_nS_x = 1)
Sync
Delay_Req
TRANSMIT
Delay_Req
Sync
For ports 1 and 2, receive is defined as data from the PHY (from the outside world) and transmit is
defined as data to the PHY. This is consistent with the point-of-view of where the partner clock resides
(LAN9311/LAN9311i receives packets from the partner via the PHY, etc.). For the time stamp module
connected to the Host MAC (Port 0), the definition of transmit and receive is reversed. Receive is
defined as data from the switch fabric, while transmit is defined as data to the switch fabric. This is
consistent with the point-of-view of where the partner clock resides (LAN9311/LAN9311i receives
packets from the partner via the switch fabric, etc.).
As defined by IEEE 1588, and shown in Figure 11.2, the message time stamp point is defined as the
leading edge of the first data bit following the Start of Frame Delimiter (SFD). However, since the
packet contents are not yet known, the time stamp can not yet be loaded into the capture register.
Therefore, the time stamp is first stored into a temporary internal holding register at the start of every
packet.
Preamble
Octet
Message Timestamp
Point
Ethernet
Start of Frame
Delimiter
First Octet
following
Start of Frame
1
1
1
1
1
111
0
0
0
0
0
0
0000000
bit time
Figure 11.2 IEEE 1588 Message Time Stamp Point
SMSC LAN9311/LAN9311i
157
DATASHEET
Revision 2.0 (02-14-13)