PXB4219E Datasheet, PDF (81/290 Pages) Infineon Technologies AG – Interworking Element for 8 E1/T1 Lines

4.8
Loopback Modes
IWE8, V3.4
PXB 4219E, PXB 4220E, PXB 4221E
Operational Description
4.8.1 Upstream Loop
The Upstream Loop block (UL) allows cells that are received at the Framer Interface and
forwarded to the UTOPIA Receive Interface to be send back via the UTOPIA Transmit
Interface to the Transmitter Interface. The UL block contains a buffer of 4 ATM cells.
To activate the Upstream Loop, the “p_ulp” bit in the Port Configuration Register (pcfN,
see Chapter 7.1) must be set to 1.
When a cell is available in the UL buffer, the UTOPIA transmit interface will de-assert the
TXCLAV signal, to prevent the ATM layer component from sending cells during the
processing of the loopback cell.
For ATM mode ports, all cells are looped regardless of their header. The loop is always
transparent allowing looped cells to be visible on the UTOPIA receive interface.
For AAL mode ports, it is possible to make a single channel loop using a VCI filter. When
the “vci_flt_ulp” bit in the Loopback Control Register (lpbc, see Chapter 7.11) is set to 0
all cells are looped. When the bit is set to 1, only those cells with the 5 LSB bits of the
VCI matching the “vci_val_ulp” field of the “lpbc” register will be looped. Loopback can
be switched from transparent to non-transparent by setting the “tulp” bit in the “lpbc”
register. If the loopback is non-transparent, looped cells are not visible on the UTOPIA
receive interface.
4.8.2 Downstream Loop
It is possible to loop ATM cells that are coming in on the UTOPIA transmit interface to
the UTOPIA receive interface through the Downstream Loop (DL) block. The DL block
contains a buffer of 4 ATM cells.
When a cell is available in the DL buffer and in the Output Queue, the UTOPIA receive
interface will transmit cells from both buffers with alternating priority.
To activate the downstream UTOPIA loop, the “p_dlp” bit in the Port Configuration
Register (pcfN, see Chapter 7.1) must be set to 1.
When the downstream UTOPIA loopback is active for at least one port, the UTOPIA
transmit interface will only assert the RxCLAV signal to 1 when a free space of one ATM
cell is available in both the DL buffer and the UT input buffer.
The loopback can be made transparent or non-transparent by setting the “tdlp” bit in the
Loopback Control Register (lpbc, see Chapter 7.11). If the loopback is made non-
transparent, the looped cells are not transferred to the “Cell Transmit Processing” block
CT.
Data Sheet
81
2003-01-20