Motorola MVME2300 Series - Manual (Page 174)

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Falcon ECC Memory Controller Chip Set
3
Cache Coherency Restrictions
The PowerPC 60x GBL_ signal must not be asserted in the CSR areas.
L2 Cache Support
The Falcon pair provides support for a look-aside L2 cache by
implementing a hold-off input, L2CLM_. On cycles that select the Falcon
pair, the Falcon pair samples L2CLM_ on the second rising edge of
CLOCK after the assertion of TS_. If L2CLM_ is high, the Falcon pair
responds normally to the cycle. If it is low, the Falcon pair ignores the
cycle.
Note The MVME2300 series boards have no L2 cache.
ECC
The Falcon pair performs single-bit error correction and double-bit error
detection for DRAM. (No checking is provided for ROM/Flash.) The 64-
bit wide PowerPC 60x data bus is divided into upper (DH0-DH31) and
lower (DL0-DL31) halves. Each half is routed through a Falcon which
multiplexes it with half of the DRAM data bus. Each Falcon connects to
64 DRAM data-bits and to 8 DRAM check-bits. The total DRAM array
width is 144 bits (2
× [64+8]).
Cycle Types
To support ECC, the Falcon pair always deals with DRAM using full
width (144-bit) accesses. When the PowerPC 60x bus master requests any
size read of DRAM, the Falcon pair reads 144 bits at least once. When the
PowerPC 60x bus master requests a four-beat write to DRAM, the Falcon
pair writes all 144 bits twice. When the PowerPC 60x bus master requests
a single-beat write to DRAM, the Falcon pair performs a 144-bit wide read
cycle to DRAM, merges in the appropriate PowerPC 60x bus write data,
and writes 144 bits back to DRAM.