TXC-06885BIOG Transwitch Corporation, TXC-06885BIOG Datasheet - Page 70

• 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

Envoy-CE4 Device
DATA SHEET
TXC-06885
7 0 o f 12 8
6.2.1.2 Oversubscription Mode
The SPI-3 Input interface is designed to support an Oversubscription mode. In this mode, the
far end SPI-3 Slave or Master device can ignore the backpressure exerted by the Envoy-CE4
SPI-3 Master or Slave. Since the backpressure is being ignored, it is possible that the per-
PHY Egress FIFOs can be filled to overflow. When a PHY’s Egress FIFO is filled, data from
the Input SPI-3 data bus will still be clocked into the Envoy-CE4, but it will not be written into
the PHY’s Egress FIFO. This allows the SPI-3 bus to still run and service the PHYs whose
buffers are not full.
Regardless of the Egress FIFO configuration for Store and Forward mode or Streaming
mode, all complete packets received on the SPI-3 port for a full PHY will be discarded and
counted. The only difference between Store and Forward mode and Streaming mode when
Oversubscription is being used is in the treatment of the packet that overflows the Egress
FIFO. In Store and Forward mode, the overflowing packet will be discarded and counted. In
Streaming mode, the overflowing packet will be flagged as errored into the Egress FIFO and
it will be errored on the way out of the Transmit MAC.
In PHY Layer mode, Oversubscription is always enabled. STPA/PTPA status is always
presented accurately on the external SPI-3 port.
In Link Layer mode, Oversubscription can be enabled or disabled through the
Oversubscription Enable bit (Register 0x002C Bit 4). If the Oversubscription enable bit is set
to ‘1’, the SPI-3 Master will never raise its ISPIRENB output. Setting this bit shuts off all Rx
backpressure reporting from the Envoy-CE4. If the Oversubscription enable bit is set to ‘0’,
the SPI-3 Master uses the ISPIRENB output pin to exert standard SPI-3 backpressure.
-
Operation
-
PRELIMINARY TXC-06885-MB, Ed. 6A
February 2005