PXB4340E Datasheet, PDF (48/185 Pages) Infineon Technologies AG – ICs for Communications

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This mechanism has to be triggered by the microprocessor. It is recommended to trigger it in a
0.5 s time frame, as all time-out values are determined based on this time interval. During a
SCAN all entries within the specified range of the external RAMs are accessed sequentially
using the read-modify-write access described in VHFWLRQ . The SCAN must be programmed
in a way that it covers all used RAM entries in a little less than 0.5 s. To initialize the SCAN
mechanism use register SCCONF2 (see VHFWLRQ  page 79). The SCAN is processed for
all connections inside the range selected by register SCCONF4 (see VHFWLRQ  page 80)
and register SCCONF5 (see VHFWLRQ  page 81). To initiate the SCAN bit STARTSC in
register SCCONF3 has to be set (see VHFWLRQ  page 80). The following equation can be
used to calculate the scan cycle period (SCP) :
SCP = ⁽---s---c----a---n----p----e---r---i-o----d-----^–----t---o---l--e----r--a----n---c----e---⁾----^×-----c-------y------c------l--e---f----s^{C--------o-p-----r--e--e-----r-------c------e-------l--l}
LCI_max – LCI_min + 1
with : scanperiod + tolerance < 500 ms !
Example : The AOP needs 32 cycles per cell. At a core frequency of 51.84 MHz the AOP can
process 1.62 M cells per second. If SCAN has to process e.g. 8192 connections within 350 ms
(scanperiod + tolerance) the SCP is calculated as :
SCP = ^{3----5---0----m-----s-----×}-----1---.--6---2-----M------^â‹---c--------e----s----l--l----s-- = 69.21 cells
8192
Here SCP is equal to the time the AOP needs to process 69.21 cells. The values of the register
entry SCP is of type integer. So the SCP is rounded to 69. If the result of the SCP calculation is
40 or less SCAN operation is no more guaranteed at full traffic load because SCAN operation
requires a number of empty cycles.
With each SCAN trigger two functions can be enabled independently for up- and downstream
direction: OAM function and DMA transfers. OAM functions include all the necessary actions for
AIS/RDI/CC processing, i.e. update of counters, check for time-out values and execution of state
transitions, OAM cell insertions and interrupts. The DMA function allows to transfer data to and
from the external RAM during the SCAN. The DMA function has two modes, the normal DMA
function and the compressed DMA.
In the normal DMA mode a specified dword of each external RAM entry is transferred to a range
of the microprocessor main memory. Each bit of the specified dword can be overwritten by a
specified value for all entries. So the normal DMA can be used to initialize the whole external
RAM to common values or also to verify entries of all connections.
In compressed DMA mode one dword with pre-defined bits collected from several dwords of the
external RAM is transferred to a microprocessor memory range. The pre-defined bits are status
bits and status transition bits. The status transition bits must be reset with each SCAN, which
can be achieved with appropriate settings of write and mask registers. The compressed DMA is
typically used in-service together with the OAM function (see VHFWLRQ ).
Data Sheet
2-48
04.2000