TXC-06885BIOG Transwitch Corporation, TXC-06885BIOG Datasheet - Page 77

• Manufacturer Part Number: TXC-06885BIOG
• Manufacturer: Transwitch Corporation

Specifications of TXC-06885BIOG

• Operating Supply Voltage (typ): 1.8/3.3V
• Operating Temperature Classification: Industrial
• Package Type: BGA
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Not Compliant

PRELIMINARY TXC-06885-MB, Ed. 6A
February 2005
6.5.2 PAUSE Control Frame Reception
6.5.3 PAUSE Control Frame Generation
6.5.3.1 Automatic PAUSE Frame Generation
2) The action taken when Envoy-CE4 generates a PAUSE control frame and transmits it to a
remote device.
The remote device is connected to the Envoy-CE4 via a full duplex link. Envoy-CE4 PAUSE
frame processing needs to be enabled for the PAUSE frame flow control mechanism to take
effect. An option is provided in the device to filter out the received PAUSE control frame.
Remote devices receiving Ethernet frames from Envoy-CE4 can backpressure Envoy-CE4, by
sending a PAUSE control frame to Envoy-CE4. The backpressure may be needed if the buffer
of the remote device on the link is becoming full. Upon reception of the PAUSE control frame,
Envoy-CE4 will stop transmitting frames to the remote device. If Envoy-CE4 is in the middle of
transmission of a frame, when it receives a PAUSE control frame, it will complete transmission
of the frame and then pause transmission of any further Data frames. When Envoy-CE4 is in
the pause state, it allows transmission of PAUSE control frames from the Envoy-CE4. The
period for which Envoy-CE4 stays in a PAUSE state is defined by the pause_time parameter
in the PAUSE control frame. The pause_time parameter is used as the initial value of an
internal count down timer. This timer is started as soon as the pause_time parameter is loaded
into the count down timer. Envoy-CE4 will stay in this PAUSE state until the internal timer
counts down to zero, in which case Envoy-CE4 will resume transmission of data frames to the
remote device. If a PAUSE control frame with a new non zero pause_time parameter is
received, the new pause_time is loaded into the internal down counter and the Envoy-CE4
stays in the PAUSE state for the time specified by the new pause_time. When a PAUSE frame
with a timer parameter value of zero is received, the Envoy-CE4 will resume sending data
frames to the remote device.
There are two modes for PAUSE Control Frame generation: Automatic PAUSE frame
generation and Host initiated PAUSE frame generation.
In this mode, when the remote device sends Data frames to the Envoy-CE4 and the Ingress
FIFO fills to a programmable High Watermark, Envoy-CE4’s flow control mechanism is
triggered and automatically generates a PAUSE control frame, which is sent after the current
transfer is over. Envoy-CE4 transmits the frame to the remote device and backpressures the
remote device. The pause_time value for the generated PAUSE control is programmable.
Once the PAUSE control frame is transmitted, Envoy-CE4 will re-transmit another PAUSE
control frame, every pause_retransmit_time, if a programmable Low Watermark is not reached
in the Ingress FIFO. The effect of the re-transmitted PAUSE control frame on the remote device
is that, it (remote device) is held in the PAUSE state and does not transmit data frames to
Envoy-CE4. The value of pause_retransmit_time is programmable and is kept by the pause
retransmit counter (down counter). In the event the Low Watermark is reached before the
pause retransmit counter counts down to zero, Envoy-CE4 will transmit a PAUSE control frame
with a pause_time value of zero to the remote device held in the pause state. The PAUSE
control frame with pause_time value of zero will initiate resumption of transmission of data
frames from the remote device to the Envoy-CE4.
- Operation -
Envoy-CE4 Device
DATA SHEET
TXC-06885
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