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| 型号： | GT-48208 |
| 厂商： | Galileo Technology Services, LLC |
| 英文描述： | Advanced Switched Ethernet Controllers for 10+10/100 BaseX(高级交换式 10+10/100 BaseX以太网控制器) |
| 中文描述： | 先进的交换式以太网控制器的10 10/100 BaseX（高级交换式10 10/100 BaseX以太网控制器） |
| 文件页数： | 72/135页 |
| 文件大小： | 1619K |
| 代理商： | GT-48208 |
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GT-482xx Switched Ethernet Controllers for 10+10/100 BaseX
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The port continues to transmit its pending packet, regardless of the collision detection, and does not fol-
low the usual Backoff Algorithm. Additional packets pending for transmission, are transmitted, while
ignoring the internal collision indication. This frees the port's transmit buffers which would otherwise be
filled up at the expense of the other ports' buffers. The assumption is that Partition state represents a
system failure situation (bad connector/cable/station), thus dropping packets is a small price to pay vs.
the cost of halting the switch due to full buffers.
The Partition Indication is available via the LED interface (both the status led - blinking twice, and a ded-
icated led - on constantly).
8.11.3 Exiting from Partition State
The port exits from Partition state at the end of a successful packet transmission or packet reception. A successful
packet transmission is declared if no collisions were detected during packet transmit or receive. If the interrupt is
not masked, the GT-482xx issues an interrupt to the CPU upon exiting from Partition state, and clears the partition
bit of that port in the Status register.
8.12
Back Pressure
The GT-482xx implements a back-pressure algorithm when it is operating only in half-duplex mode. Back pres-
sure is enabled by setting the BackPressureEn bit in the Port Control register (also sampled at reset from pin).
The GT-482xx enters into back-pressure mode when the buffers allocated to a port exceed the RxThreshold value
(The user should not disable the Per-port Rx Buffer threshold when using Backpressure). In back-pressure mode,
the GT-482xx transmits a JAM pattern for a programmable value of time (JAM_LENGTH). The IPG between two
consecutive JAM patterns (or between the last transmit and the first JAM) is also a programmable value
(JAM_IPG). When a
packet is transmitted
during back
pressure
it is transmitted with a
gap
of
IPG_JAM_TO_DATA after the transmission of the JAM pattern.
8.13
Flow Control
The GT-482xx implements the IEEE 802.3x flow control standard on any full-duplex port. This mode is activated
by setting the FlowContEn bit in the Port Control register (sampled at reset from pins). When the GT-482xx
receives a PAUSE packet it avoids transmitting a new packet from this port for the period of time specified in the
received PAUSE packet.
A received packet is recognized as flow control if it was received without errors and is either one of the following:
DA = 01-80-C2-00-00-01 and type=88-08 and MAC_Control_Opcode=01
DA = (The port address) and type=88-08 and MAC_Control_Opcode=01. The 48bit port address is in
the registers Source_Address_Low, Source_Address_High and Port_Control[Sa<3:0>]. This address is
used as source address for PAUSE packets that the GT-482xx generates (to DA=01-80-C2-00-00-01)
The GT-482xx sends a PAUSE packet on a port, when the number of buffers allocated to this port exceed a pro-
grammable threshold (as specified by FlowContThrHigh field in Rx Threshold Register. The user should not dis-
able the Per-port Rx Buffer threshold when using Flow-Control. The PAUSE packet will be sent with the parameter
equal to 0xFFFF. The transmitting device is expected to stop transmitting to the specific GT-482xx port for suffi-
cient time to enable the GT-482xx to release its buffers. When the number of buffers drops below the FlowCont-
ThrLow number, the GT-482xx sends a PAUSE packet with its parameter equal to 0x0 to indicate to the
transmitter that the GT-482xx is ready to receive packets on that link.
To prevent deadlocks on the network (due to loss of PAUSE packets), the GT-482xx will periodically send PAUSE
packets every 50mSec (for the 10Mbps ports, every 500mSec). PAUSE packets with parameters equal to 0xFFFF
are sent every 50mSec when the number of buffers allocated to this port exceed a programmable threshold (Flow-
ContThrHigh). PAUSE packets with parameters equal to 0x0 are send every 50mSec when the number of buffers
allocated to this port is less than or equal to FlowContThrLow number.
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