MSC8144E Reference Manual, Rev. 3
4-6
Freescale
Semiconductor
Chip-Level Arbitration and Switching System (CLASS)
4.2.2.1.2 Weighted Arbitration
The CLASS arbiter supports limited weighted arbitration, as shown in Figure 4-3. Weighted
arbitration is needed to apply non-uniform distribution of the bandwidth from all initiators toward
each target. Weighted arbitration is configurable per CLASS target and gives configurable
weights to each initiator. The CLASS arbiter ensures that when a weighted initiator wins the
arbitration, it performs 1 consecutive transactions before transferring control to another
initiator with the same or lower priority level.
4.2.2.1.3 Late Arbitration
In late arbitration mode, the request is initiated by the class arbiters as late as possible. At the end
of a data burst, this can give better or worse performance for the initiators. The performance
depends on the bursty character of the application and the utilization to the target. This mode is
activated/deactivated by the appropriate bit in the CnACR (see Section 4.7.25, CLASS
Arbitration Control Register (CnACR)).
4.2.2.1.4 Priority Masking
When CnACR[PME] is set, the class arbiters are configured to preserve cycle slots for low
priority accesses. They reserve 1/16 of all cycles for priority 0, 2/16 of all cycles for priority 1 or
0, and 2/16 of all cycles for priority 2, 1, or 0. This mode can decrease overall performance. This
is one of two approaches to eliminate starvation. The other is to use auto-priority upgrade.
4.2.2.1.5 Auto Priority Upgrade
This mode is activated by setting the CnPACRx[AUE] bit (see Section 4.7.4, CLASS Priority
Auto Upgrade Control Registers (CnPACRx)). When active, a pending request has its priority
upgraded to the next higher priority after a specified number of cycles specified by
CnPAVRx[AUV] (see Section 4.7.3, CLASS Priority Auto Upgrade Value Registers
(CnPAVRx)). The upgrade level and timing depend on the current priority value assigned, as
follows:
Figure 4-3. Weighted Arbitration Structure (Example)
Highest Hierarchy CLASS
low hierarchy CLASSx
Initiator 6
Initiator 5
Initiator 4
Initiator 1
we
ig
h
t=
0
low hierarchy CLASSy
we
ig
h
t=
0
we
ig
h
t=
0
we
ig
h
t=
0
we
ig
h
t=
0
we
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h
t=
0
we
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h
t=
0
we
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h
t=
0
we
ig
h
t=
0
we
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h
t=
0
we
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h
t=
0
we
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h
t=
0
Initiator 2
Initiator 3
we
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h
t =
0
we
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h
t =
0
we
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h
t =
0
we
ig
h
t =
3
weight = 2
weight = 5
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...