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CHAPTER 5 SAR FUNCTION
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(8) Unassigned (idle) cell generator function
The user can use one or more shapers as unassigned cell generators to limit the band used by the active
VC. A shaper set as an unassigned cell generator functions as if it were linked to a VC that transmits a cell
consisting of an all-zero header and all-zero data. By assigning a priority higher than that of the data
transmission shaper to a shaper specified as an unassigned cell generator, the band used by the data can
be limited.
The unassigned cell may be switched to an idle cell according to the ICM bit of the GMR register.
An unassigned cell generator is selected by means of the following procedure.
<1>
Set bits 31 and 30, the "a" and "u" bits, of the shaper pointer entry of the shaper to be selected as an
unassigned cell generator, to 1.
<2>
Set parameters in the scheduler register. At this time, set active bit "A" to 1 at the same time as
enable bit E.
Cautions 1. A normal VC cannot be linked to a shaper that is specified as being an unassigned cell
generator.
2. The host need not set the shaper pointer entry "a" bit and scheduler register "A" bit to
1, except when using the unassigned cell generator function. For a data transmit
shaper, the
μ
PD98405 automatically sets these bits to 1.
3. The unassigned cell generator cannot be used in a mode in which an unassigned cell
for rate adjustment is not to be transmitted (while the UID bit of the GMR register is set
to 1).
Example:
Shaper 0:
Set as the unassigned cell generator, and I/M = 1/3
Shaper 1:
Set with usual data cell, I/M = 1/1
VC
TX
VC
U/I
VC
VC
U/I
VC
VC
U/I
VC
VC
U/I
VC
VC
U/I
VC
VC
U/I
PHY
TX
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
U/I
PHY
U/I: Unassigned cell if ICM = 0
Idle cell if ICM = 1
VC: Data cell
: Cell generated by the unassigned cell
generator
Those data cells to be transmitted are embedded between unassigned cells.
When there is no data cell to be transmitted