SMSC LAN9312 - Manual (Page 58)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08) 58 SMSC LAN9312
DATASHEET
6.2.3 Flow Control Enable Logic
Each switch fabric port (0,1,2) is provided with two flow control enable inputs per port, one for
transmission and one for reception. Flow control on transmission allows the transmitter to generate
back pressure in half-duplex mode, and pause packets in full-duplex. Flow control in reception enables
the reception of pause packets to pause transmissions.
The state of these enables is based on the state of the ports duplex and Auto-negotiation settings and
the values of the corresponding Manual Flow Control register (
Port 1 Manual Flow Control Register
(MANUAL_FC_1) , Port 2 Manual Flow Control Register (MANUAL_FC_2) , or Port 0(Host MAC)
Manual Flow Control Register (MANUAL_FC_MII) ). Table 6.1 details the switch fabric flow control
enable logic.
When in half-duplex mode, the transmit flow control (back pressure) enable is determined directly by
the BP_EN_x bit of the ports manual flow control register. When Auto-negotiation is disabled, or the
MANUAL_FC_x bit of the ports manual flow control register is set, the switch port flow control enables
during full-duplex are determined by the TX_FC_x and RX_FC_x bits of the ports manual flow control
Figure 6.2 Switch Fabric CSR Read Access Flow Diagram
Idle
Write
Command
Register
Read
Command
Register
Read Data
Register
CSR_BUSY = 0
CSR Read
CSR_BUSY = 1
Idle
Write
Command
Register
Read
Command
Register
CSR_BUSY = 0
CSR Read Auto
Increment /
Decrement
CSR_BUSY = 1
Write
Command
Register
Read Data
Register
last
data?
Yes
No Read Data
Register
min wait period
min wait period min wait period