Functional Description
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
4-5
multiplexer and arbiter module. The CLASS prevents the possibility of simultaneous accessing to
more than one target by the same initiator. If there are accesses from one initiator to different
targets, the expander module start the transactions to other targets only after all the open accesses
to the current target are completed. The expander module is a sampling stage of transaction. For
each request (a attribute), write data is sampled from the initiator and driven to the
normalizer module through multiplexer and arbiter module in the following clock cycle; read
data is sampled from the normalizer module through multiplexer and arbiter module and driven
to the initiator in the following clock cycle.
4.2.2
Multiplexer and Arbiter Module
The multiplexer and arbiter module connects to all the expander modules on one side and to a
dedicated normalizer module on the other side. The multiplexer and arbiter module block is a
pure logic data path design, that supports up to 16 initiators, performs an arbitration, and
concentrates them towards a specific target normalizer module.
4.2.2.1 Atomic Stall Unit (ASU)
The atomic stall unit (ASU) maintains coherency by stalling all read atomic accesses while an
atomic operation is open. An atomic operation starts when an initiator performs a read atomic
access from a target (and checks to see whether it is appropriate to modify some bits), and ends
when the initiator gets the end of transaction signal for write atomic access. The ASU includes an
Atomic Open flag which is set when an initiator receives the acknowledge for its read atomic
access. While the Atomic Open flag is set, all the read atomic accesses from other initiators are
stalled. When the atomic operation ends, the multiplexer clears the Atomic Open flag in the ASU.
Note:
Atomic operations are only supported in M2 memory and not in any other memory.
4.2.2.1.1 CLASS Arbiter
The CLASS arbiter performs weighted arbitration algorithm for requestors simultaneously using
a pseudo round-robin arbitration algorithm for each of the priority levels and chooses the highest
level request. The CLASS arbiter supports four priority levels, where 3 is the highest and 0 is the
lowest. The arbitration operation can be done every clock cycle or delayed according to the
number of datums of acknowledged transaction (Late Arbitration mode). The CLASS arbiter
supports priority upgrade, so the initiator can upgrade the priority level at any clock cycle.
To eliminate starvation for initiators with low priority, the Masking Priority should be enabled.
Starvation can occur when the higher priority initiators access continuously and the lower priority
initiators can not perform any access (no priority upgrade ability by the initiator and auto priority
upgrade in the expander module is disabled). When the Masking Priority is enabled, the arbiter
dedicates slots for lower priority initiator in which the higher priority initiators are masked.
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 ...