PXF4336 Datasheet, PDF (142/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Operational Description
TstepC is configured per direction by the field TstepC[2:0] described in “USCONF/
DSCONF” on Page 295. Internally the shaper use a derived value Tstep with the
following interpretation:
Tstep = 2^{TstepC – 8}
(14)
This renders Tstep in the range 1/2 ... 1/256.
Smaller values for TstepC and in consequence Tstep imply lower shaping rates.
Given a particular TP, the resulting PCR shaping rate is calculated as follows:
PCR_RS
=
S_-----Y_----S_-----C_----L_----K_--
32
×
Tstep
×
-⁶---⁴---
TP
(15)
Vice versa, for a given PCR, the corresponding TP value is calculated as:
TP =
S_-----Y_----S_-----C_----L_----K_--
32
×
Tstep
×
-------⁶----⁴--------
PCR_RS
(16)
The value of parameter TP is constrained internally to:
TP ≤ 2¹⁶ – 2⁶
(17)
Therefore, TP_max = 65472.
Though possible to specify, very low values of TP do not make much sense, because
the shaper is limited by PCR_RSmax in any case (see Equation (13)). Together with
Equation (15) this leads to the following constraint on TP:
TP ≥ max(1, Tstep × 128)
(18)
The following special case must be considered:
TP = 0 disables the shaper, connecting the queue directly to the level 1 schedulers (RR
/ WFQ).
Data Sheet
142
2001-12-17