PXF4336 Datasheet, PDF (55/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Functional Description
3.2.6 Queue Congestion Indication Unit
Some system implementations are based on in-system flow control mechanisms that
require congestion indication information from the downstream queues on a per queue
basis (i.e. typically per connection). As an example, a traffic management optimized IP
over ATM implementation requires a control link between the ATM traffic management
and the packet scheduling unit.
Queue status information (e.g. the queue length) can generally be obtained by reading
the Queue Configuration Table (QCT). For a large number of queues (e.g. 8k) and
typical time constraints of control loop mechanisms, a software based queue monitoring
is not feasible.
The Queue Congestion Indication interface (QCI) is a serial interface providing a bit-
pattern with queue-specific threshold exceed information. Each bit represents the queue
number corresponding to the bit position. A ‘1’ means congestion, i.e. the queue-specific
threshold is currently exceeded. The bit-pattern is generated with minimum HDLC
framing and can be limited to 1024, 2048, 4096 or 8192 bits payload, depending on the
number of queues that need to be monitored.
Global configuration of the QCI unit is performed in register “DQCIC” on Page 229. The
queue specific thresholds are programmed in table QCIT via transfer register “QCIT” on
Page 287.
3.2.7 Clocking System
The clocking system of the ABM-P distinguishes the core clock, the ERC clock, and the
UTOPIA Interfaces whereas each UTOPIA Interface and direction (transmit/receive) is
clocked independently, as shown in Figure 3-7.
The ERC clock can be derived internally from either the SYSCLK signal or the internal
core clock. Programmable DPLLs allow for a wide range of external clocks to derive the
required core clocks.
In addition to the major clock domains, the serial QCI Interface is also clocked
independently.
Data Sheet
55
2001-12-17