PXF4336 Datasheet, PDF (114/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

3.5.2.4 AVT (Context RAM)
Chapter 3.6.9 provides the details.
ABM-P
PXF 4336 V1.1
Functional Description
3.5.2.5 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The basic function of the Scan Unit is to periodically refresh outdated variables and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, needed by the ABR-ER and ABR-VS/VD mechanisms.
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.
SYSCLK
40 ..60 MHz
Divider
/32
CellClk * 2**TstepC
Tnow
24 bit
ER
VBR
Divider
/256
Period
1.25ms
Programmble
Divider
Period
10ms
ms125count
8bit
ms10count
8bit
VS/VD
Figure 3-49 SCAN Timer Generation
The 40...60 MHz SYSCLK is divided by 32 to obtain a cell clock CellClk.
The Tnow counter with 24-bit width increments by 2**TStepC every CellClk. The value
of this counter is made available as relative time reference to other blocks. Parameter
TStepC is set in Register 70 "USCONF/DSCONF" on Page 295.
The absolute time bases are provided by dividing the CellClk first by 256 and then by a
programmable divider of 7 bit (1...127).
Timer ms125count is derived from bit 4 of the programmable divider.
Timer ms10count is derived by from bit 7 of the programmable divider.
Data Sheet
114
2001-12-17