PXB4219 Datasheet, PDF (45/290 Pages) Infineon Technologies AG – IWE8 Interworking Element for 8 E1/T1 Lines

PXB4219 / PXB4220 / PXB4221
Operational Description
4
Operational Description
4.1
ATM Transmit Functions
For ports configured to ATM mode the following data flow is valid:
The Cell Transmit Processing block is responsible for:
• Cell discarding
• Write ATM cells except of UDF octet to ATM Transmit Buffer
The Octet Transmit Processing block is responsible for:
• Reading octets from ATM Transmit Buffer
• Cell rate de-coupling: idle/unassigned cell insertion
• Cell payload scrambling
• HEC generation
The ATM transmit functions are controlled by the internal registers “catm”, “atmc” and
“txid”. The features controlled by these registers are common to all ATM ports.
Some features of the ATM transmit functions can be controlled per port, by programming
the port specific “ATM Transmit Reference Slot” in the internal configuration RAM2
4.1.1 Operation
4.1.1.1 ATM Transmit Buffer Filling Level
The amount of buffered data in transmit direction of each port is adjustable in granularity
of bytes or cells. This allows a controlled transmission delay while maintaining a
continuous ATM cell flow. The feature is implemented using the port specific back
pressure mechanism of the UTOPIA interface (Chapter 5.2.2).
The granularity and range of filling level are set independently per port in the “p_thr_m”
bits of the Port Configuration Registers (“pcfN”, see Chapter 7.1). The port specific
threshold value is defined via the corresponding Threshold Port Register (“thrspN”, see
Chapter 7.38 to Chapter 7.41)
2 Modes are supported:
• Mode 1 (p_thr_m = 01_B) allows the definition of threshold values in the range of 0 to
255 cells. The actual value equals the contents of thrspN.
• Mode 2 (p_thr_m = 10_B) allows the definition of threshold values in the range of 0 to
222 bytes. The actual value equals 53 * C + B, with C representing the 2 most
significant bits of thrspN and B representing the 6 least significant bits of thrspN.
All other values of p_thr_m will switch off this feature and reset the internal counter.
To avoid deadlock conditions, the contents of the common 8 cell UTOPIA input buffer
will always be flushed into the port specific Transmit Buffers independent from their back
Data Sheet
45
2002-05-06