PXF4336 Datasheet, PDF (141/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Operational Description
4.2.2.3 Programming the Common Real-Time Bypass
The Common Real-Time bypass (CRT) is denoted by the reserved logical queue
identifier QID = 0. The rate assigned to the CRT bypass is programmed in the same way
as the SB rates. The parameters CRTIntRate and CRTFracRate are described in
registers “UCRTRI/DCRTRI” on Page 327 and “UCRTRF/DCRTRF” on Page 328.
4.2.2.4 Programming the SDRAM Refresh Empty Cell Cycles
The programming of the rate for the internal SDRAM refresh generator is done by
calculating the integer and fractional parts of the dimensionless value T_empty according to
the SB formulas (Equation (8) and Equation (9)).
T_empty is constrained by the need to allow a minimum number of empty cell cycles for the
internal SDRAM refresh generator according to:
T_e
mp
ty
≤
S_-----Y_----S_-----C_----L_----K_-----×_-----R_-----e_----f_--r_--e_----s_---h_----P_----e_----r_--i_--o_----d_-
32 × RefreshCycles
(12)
Given values of RefreshPeriod = 64ms, RefreshCycles = 4096 then
at SYSCLK = 51.84 MHz, T_empty = 25.3125, T_empty(i) = 25, T_empty(f) = 80
at SYSCLK = 60 MHz, T_empty = 29.2968, T_empty(i) = 29, T_empty(f) = 76
This renders PCR_empty = 64000 [cells/s] in both cases.
In case additional bandwidth needs to be reserved (e.g. for multicast operation in sub-
sequent devices), a second maximum condition for parameter T_emptyMC can be derived
depending on the empty cell rate required for multicast bandwidth reservation.
The cell rate for the empty cell cycles PCR_empty is programmed by setting T_empty(i) and
T_empty(f), referred to as ECIntRate and ECFracRate in the corresponding registers
“UECRI/DECRI” on Page 312 and “UECRF/DECRF” on Page 313.
4.2.2.5 Programming the PCR Limiter
For each logical queue, an optional peak rate shaper can be programmed.
Each cell passing the PCR limiter needs at least 2 cell cycles to emit. This limits the
maximum PCR that can be shaped to:
PCR_RSmax
=
S_-----Y_----S_-----C_----L_----K_--
32
×
1_--
2
[cells ⁄ s]
(13)
The resolution of the PCR limiter is determined by the global parameter TstepC,
common for all shapers in an ABM-P core.
Data Sheet
141
2001-12-17