Table 3.6 Request Metering Decrement Value - IDT 89HPES64H16G2 User Manual

IDT Switch Core
Notes
PES64H16G2 User Manual
The Decrement Value Adjustment (DVADJ) field represents a sign-magnitude fixed point 0:4:11 number
(i.e., a positive fixed-point number with 4 integer bits and 11 fractional bits).
– DVADJ field provides fine grain programmable adjustment of the value by which the counter is
decremented.
– The sign bit in the DVADJ field should not be set to negative (i.e., 0b1).
Figure 3.6 shows the decrement value and the decrement value adjustment.
Fixed Decrem ent Value
Decrem ent Value Adjustm ent
Actual Decrem ent Value
Figure 3.6 Decrement Value and Decrement Value Adjustment
The counter stops decrementing when it reaches zero or when a rollover occurs (i.e., the decrement
causes it to become negative).
Link Link
Width Speed
x1 Gen 1
x2 Gen 1
x4 Gen 1
x8 Gen 1
x1 Gen 2
x2 Gen 2
x4 Gen 2
x8 Gen 2
The computation that occurs on each clock tick by the request metering counter is shown Figure 3.7.
0 DW ords
Sign 4 bits
0 DW ords
Sign 4 bits
0 DW ords
Sign 4 bits
Decrement Value
0x02
0x04
0x08
0x10
0x04
0x08
0x10
0x20

Table 3.6 Request Metering Decrement Value

3 - 11
Nibbles 0000 0000
3 bits 8 bits
Fractional Part
11 bits
Fractional Part
11 bits
Notes
Corresponds to 1 Byte per clock tick
Corresponds to 2 Bytes per clock tick
Corresponds to 4 Bytes per clock tick
Corresponds to 8 Bytes per clock tick
Corresponds to 2 Bytes per clock tick
Corresponds to 4 Bytes per clock tick
Corresponds to 8 Bytes per clock tick
Corresponds to 16 Bytes per clock tick
April 5, 2013