
MOTOROLA
Chapter 9. Core Interface Operation
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9-19
Address Bus Tenure
between the two transfers. Also, the two bus operations associated with a misaligned
ecowx
may be interrupted by an
eciwx
bus operation, and vice versa. The core guarantees that the
two operations associated with a misaligned
ecowx
cannot be interrupted by another
ecowx
operation.
Because a misaligned external control address is considered a programming error, the
system may choose to assert core_tea or otherwise cause an exception when a misaligned
external control bus operation occurs.
9.3.2.6
Transfer Code (core_tc[0:1]) Signals
The core_tc0 and core_tc1 signals provide supplemental information about the
corresponding address. Note that the core_tc
x
signals can be used with both core_tt_in[0:4]
and core_tt_out[0:4], and both core_tbst_in and core_tbst_out signals to further define the
current transaction.
Table 9-9 shows the encodings of the core_tc[0:1] signals.
9.3.3
Address Transfer Termination
The address tenure of a bus operation is terminated when completed with the assertion of
core_aack, or retried with the assertion of core_artry_in. The G2 core does not terminate
the address transfer until the core_aack (address acknowledge) input is asserted; therefore,
the system can extend the address transfer phase by delaying the assertion of core_aack to
the G2 core. core_aack can be asserted as early as the bus clock cycle following core_ts_in
(see Figure 9-6), which allows a minimum address tenure of two bus cycles. However,
when the core clock is configured for 1:1 or 1.5:1 processor core-to-bus clock mode, the
core_artry_out snoop response cannot be determined in the minimum allowed address
tenure period. Thus, in a system with two or more G2 cores using 1:1 or 1.5:1 clock mode,
core_aack must not be asserted until the third clock of the address tenure (one address wait
state) to allow the snooping G2 cores an opportunity to assert core_artry_in on the bus. For
other clock configurations (2:1, 2.5:1, 3:1, 3.5:1, and 4:1), the core_artry_out snoop
response can be determined in the minimum address tenure period, and core_aack may be
asserted as early as the second bus clock of the address tenure. As shown in Figure 9-6,
these signals are asserted for one bus clock cycle, three-stated for half of the next bus clock
Table 9-9. Transfer Code Encoding
core_tc[0:1]
Read
Write
0 0
Data transaction
Any write
0 1
Touch load
N/A
1 0
Instruction fetch
N/A
1 1
(Reserved)
N/A
F
Freescale Semiconductor, Inc.
n
.