PXF4333 Datasheet, PDF (112/361 Pages) Infineon Technologies AG – ABM 3G ATM Buf fer Manager

ABM-3G
PXF 4333 V1.1
Operational Description
Table 4-5 shows the accuracy of the shaping rate at some characteristic rates for three
selected values of TstepC.
Table 4-5 Shaper Accuracy as a Function of desired PCR and TstepC
desired
PCR
TstepC = 0
acc_PCR at SYSCLK = 51.84 [MHz]
TstepC = 4
TstepC = 7
32
0.000059
not possible
64
0.000138
not possible
170
0.000271
0.000009
4830
0.001774
0.000286
101957
0.006934
0.006934
353108
0.425621
0.034140
not possible
not possible
not possible
0.000007
0.001081
0.001288
Regarding the inevitable jitter (CDV) produced by the rate shaper due to its limited
accuracy, it improves towards higher shaping rates and higher values of TstepC.
The value of parameter TP derived above is programmed into the field RateFactor in
register “UQPT2T0/DQPT2T0” on Page 253.
Note: A value of 0 in field RateFactor disables both the PCR limiter and the leaky bucket
shaper. Values other than 0 in field RateFactor are ignored for queues with an
additional leaky bucket shaper enabled. The parameter TP defined there
overrides. See Section 4.2.2.6.
4.2.2.6 Programming the Leaky Bucket Shaper
Regarding the Leaky Bucket Shaper, the formulas given previously in Section 4.2.2.5
apply accordingly when substituting SCR for PCR and TS for TP.
In addition, given MBS, the parameter tauS is calculated as:
tauS
=
(MBS
–
1)
×
æ
è
T_----S_{----6--–-4----}T_----P_--øö
(20)
with tauS constrained internally to:
tauS ≤ 2¹⁶ – 2¹⁰
(21)
Therefore, tauS_max = 64512.
Data Sheet
112
2001-12-17