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CHAPTER 7 REGISTERS
319
(19) LCR (internal congestion cell rate register)
Address:
502H
Access mode: Read/write
The LCR register is used to set the cell rate used to determine whether cell rate reduction is applied. If a
VC is performing transmission at a rate less than that set in the LCR register, rate reduction is not applied
upon the detection of source internal congestion by the ABR service. To prevent rate reduction from being
applied to a VC that is performing transmission at less than a given rate upon the occurrence of internal
congestion, set that rate in the LCR register. The default value after a reset is 0. It is not possible to write
to bits 31 to 15. Upon a read, 0 is returned.
31
0
LCR
- 0 -
14
15
LCR: Sets the internal congestion cell rate, obtained using the expression shown below.
Rate = 2
e
*(1 + m/512)*nz cells/second
14
0
m
9
8
nz
e
13
(20) Scheduler registers
Each of the sixteen shapers (for VBR) has five 32-bit registers. The host sets parameters that determine
the average rate, peak rate, and priority of the shaper to be used. The
μ
PD98405 uses these registers to
store variables used for calculation during traffic control, and flags indicating the statuses of the shapers.
Two priority registers (addresses: 50H & 51H) are provided for the ABR scheduler. These registers are
used to set the priorities of the ABR scheduler (in-rate/out-of-rate). For the ABR service priority, set a
value less than that of VBR, but greater than UBR.
The default values of all these registers are 0. It is not possible to write to bits 26 to 5 of the Pri & Status
register, or to bits 26 to 3, 1, and 0 of the Priority register. Upon a read, 0 is returned.