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CHAPTER 5 SAR FUNCTION
150
Table 5-3. Scheduler Register Bit Functions
Bit
Description
I (8 bits), M (24 bits)
Average rate. These bits specify the average rate parameter in cell units. The
average rate is specified as I/M, where I cells are transmitted for every M cells.
P (peak, 8 bits)
Peak cell rate. These bits specify a minimum time difference between two
consecutive cells transmitted over a channel linked to the shaper. The value is in
cell units.
C (credit, 8 bits)
Credit. These bits specify the maximum number of credits that can be accumulated
by a shaper. The I, M, P, and C parameters control the maximum cell count
(maximum burst size) for which continuous transmission is possible at the peak rate.
AGM
(Aggregate mode, 1 bit)
Selects the transmit rate control mode.
0: Normal mode. The set rate parameter is converted to VC units.
1: Aggregate mode. The set rate parameter is converted to shaper units.
See
Section 5.4.4 (9)
for details.
Priority. These bits specify the priority of the shaper. "00000" is the highest priority,
while "11111" is the lowest priority.
PRIORITY (priority, 5 bits)
E (enable, 1 bit)
Enables the shaper.
Figure 5-22. Example of Parameter Settings
Example
I/M = 1/3 (average rate)
P = 1 (peak rate)
C = 4 (maximum number of cells that can be transmitted successively at the peak rate)
VC#a
VC#a
VC#a
VC#a
VC#a
VC#a
VC#a
UNC
UNC
UNC
UNC
UNC
UNC
UNC
UNC
UNC
UNC
I/M = 1/3
PHY
P = 1
Peak rate transmission C = 4
Average rate transmission
VC#a: Data cell
UNC: Unassigned cell
The
μ
PD98405 internally generates variables for each shaper, based on the parameters set by the user,
then executes an algorithm operation. Each shaper has flags that indicate the status of the shaper. These
variables and flags are stored in each scheduler register and are managed by the
μ
PD98405. The register
is enabled and updated if the enable bit "E" of each shaper is set to "1" and when the shaper enable bit
"SE" of the GMR register is set to "1" by the host.