
MOTOROLA
Chapter 9. Core Interface Operation
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9-39
Optional Bus Configurations
An example of a two-beat data transfer (with core_drtry asserted during each data tenure)
is shown in Figure 9-21.
Figure 9-21. 32-Bit Data Bus Transfer (Two-Beat Burst with DRTRY)
The G2 core selects 64- or 32-bit data bus mode at startup by sampling the state of the
core_tlbisync signal at the negation of core_hreset. If the core_tlbisync signal is negated at
the negation of core_hreset, 64-bit data mode is entered by the core. If core_tlbisync is
asserted at the negation of core_hreset, 32-bit data mode is entered.
9.6.2
No-core_drtry Mode
The G2 core supports an optional mode to disable the use of the data retry function provided
through core_drtry. The no-core_drtry mode allows the forwarding of data during load
operations to the processor core one bus cycle sooner than in the normal bus protocol.
The bus protocol specifies that, during load operations, the memory system can normally
cancel data that was read by the master on the bus cycle after core_ta was asserted. This late
cancellation protocol requires the core to hold any loaded data at the bus interface for one
additional bus clock to verify that the data is valid before forwarding it to the processor
core. For systems that do not implement the core_drtry function, the core provides an
optional no-core_drtry mode that eliminates this one-cycle stall during all load operations
and allows for the forwarding of data to the internal CPU immediately when core_ta is
recognized.
When the G2 core is in no-core_drtry mode, data can no longer be canceled the cycle after
it is acknowledged by an assertion of core_ta. Data is immediately forwarded to the
core_ts_out
core_abb_out
ADDR
core_tbst_out
core_aack
core_artry_out
core_dbb_out
core_dh[0:31]
core_ta_out
core_drtry
core_tea_out
0
1
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