PXF4333 Datasheet, PDF (90/361 Pages) Infineon Technologies AG – ABM 3G ATM Buf fer Manager

3.4.5 Supervision Functions
ABM-3G
PXF 4333 V1.1
Functional Description
3.4.5.1 Cell Header Protection
To guarantee that the cell header is not corrupted by the external SDRAM, it is protected
by an 8-bit interleaved parity octet. It extends over the 5-octet standard header including
the UDF1 octet. The BIP-8 octet is calculated for all incoming cells and stored at the
place of the UDF2 octet. When a cell is read out, the BIP-8 is calculated again and is
compared with the stored BIP-8. In case of a mismatch, an ’BIP8ER’ (Register 101:
ISRU, Register 102: ISRD) interrupt is generated and the cell is discarded or not,
depending on the configuration. cell header protection by BIP-8 can be disabled to
achieve UDF2 transparency.
3.4.5.2 Cell Queue Supervision
The queueing of cells in the ABM-3G is implemented mostly by pointers. To detect
pointer errors, the number of the queue in which the cell is stored is appended to the cell
in the external cell storage SDRAM. When the cell is read out later, the selected queue
number is compared to the QID stored with the cell. In case of a mismatch, a ’BUFER4’
(Register 101: ISRU, Register 102: ISRD) interrupt is generated. See also “Upstream/
Downstream Cell Flow Test Registers” on Page 156.
3.4.5.3 Scan Unit
The basic function of the Scan Unit is to periodically refresh outdated variables and
detect idle connections.
The Scan Unit generates the (relative) cell clock Tnow needed by the VBR shaping
mechanism and two (absolute) 1.25 ms and 10 ms clocks referred to as ms125count
and ms10count.
The Scan Unit accesses the complete AVT Context RAM periodically every 1.25ms. In
a first step dword0 containing the Config(6:0) bits is read. These bits are interpreted and
then in a second step the respective dwords are read which contain the time information.
In case of time-outs the information is modified and written back.
Data Sheet
90
2001-12-17