MSC8144E Reference Manual, Rev. 3
11-10
Freescale
Semiconductor
Internal Memory Subsystem
11.4.1 CLASS
The Chip Level Arbitration and Switching System (CLASS) non blocking, interconnect fabric
used in the L2 ICache is the same model as that used for linking the DSP core subsystems to the
MSC8144E peripherals and MBus (see Chapter 4, Chip-Level Arbitration and Switching System
(CLASS) for details). There are two CLASS modules in the L2 ICache, referred to as the CLASS
initiator and the CLASS target. The CLASS initiator supports arbitration between multiple
initiators and multiple targets. The CLASS initiator normalizes transactions using specified L2
ICache parameters. Non-cacheable accesses are supported by CLASS initiator address decoding.
The L2 ICache CLASS initiator supports four initiators (the four DSP core subsystems) and three
targets (ports 1 and 2 for cache memory interleaving and port 0 for the CLASS target for a
non-cacheable path). The CLASS initiator gets fetch requests from the DSP core subsystems and
either
passes cacheable requests to the relevant L1 ICache, or
passes non-cacheable requests (single or burst) to the CLASS target.
When the requested data is ready, the CLASS initiator transfers it back to the DSP core
subsystem that initiated the access.
The interleave between the two L2 ICache banks is done by the CLASS initiator using the lsb of
the 6-bit cache index. After interleaving, the lsb of the 6 bit index is removed and each bank uses
a 5-bit index, as shown in Figure 11-2.
Each cache way includes 32 cache lines (5 bit index after the 6 bit index is used to interleave
between the banks). Each line includes 256 bytes of data, 16 bytes in each VBR. To locate the
instruction cache line that matches the access, the tag is compared to those which are stored in the
cache lines. All lines are compared simultaneously. In case of line match and valid status of the
appropriate VBR in the cache, the access is served by cache memory without any latency penalty
(unless there is a memory conflict).
Each access is received by the CLASS initiator and is transferred (as single transfers) to the bus
bridge according to its address range. The bridge accesses activate the CLASS port, and in case
of a hit, the port returns the data toward the bridge. In case of a miss, the fetch unit in the bank
issues fetch requests to the higher-level memory, and can pre-fetch more data than requested,
limited at most by the end of the cache line (the user can enable or disable the prefetch), to reduce
the performance impact due to subsequent accesses.
The CLASS initiator port 0 is enabled out of reset and gets the full address range
(0x00000–0xFFFFF). Port 1 should be enabled and gets an address range defined by the user in
L2IC_CSA and L2IC_CEA; the reset range is 0x00000–0xFFFFF, but the cacheable window is
disabled, which means that after reset all accesses are treated as non-cacheable. Port 2 is disabled
after reset and accesses pass through it according to the interleaving.
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 ...