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MPC7400 RISC Microprocessor Users Manual
MPX Bus Signal ConTguration
8.4.6.2 Data Transaction Index (DTI[0:2])Input
The 60x bus transaction reordering scheme is implemented with the DBWO signal. The
MPX bus mode can be conTgured to support a generalized reordering scheme using the
new 3-bit data transfer index (DTI[0:2]) input signals.
The DTI signals can be bused or point-to-point. They must be driven valid by the system
arbiter on the cycle before a data bus grant (DBG). They are sampled on each bus clock
cycle by the MPC7400 and are qualiTed by the assertion of DBG on the following cycle.
The data transfer index is a pointer into the MPC7400s queue of outstanding transactions,
indicating which transaction is to be serviced by the subsequent data tenure. Note that this
protocol is a generalization of the DBWO protocol in which the assertion of DBWO
indicated that the Trst write operation in the queue was to be serviced. For example,
DTI = 0b000 means that the oldest transaction is to be serviced, DTI = 0b001 means the
second oldest transaction is to be serviced up to DTI = 0b101 meaning the 6th oldest
transaction is to be serviced. Note that because the MPC7400 only supports six outstanding
data transactions, the maximum setting for DTI is 0b101.
Data tenure reordering can be disabled by setting DTI[0:2] to 0b000. This setting causes
the MPC7400 to select always the oldest transaction in the outstanding transaction queue.
See Section 9.6.2.2.8, òData Tenure Reordering in MPX Bus Only.ó
Following are the state meaning and timing comments for the DTI[0:2] signals.
State Meaning
AssertedThe DTI[0:2] signals act as a pointer into the queue of
outstanding transactions for the MPC7400, indicating which
transaction is to be served by the subsequent data tenure. For
example, DTI = 0b000 means that the oldest transaction is to be
serviced, DTI = 0b001 means the second oldest transaction is to be
serviced up to DTI = 0b101 meaning the 6th oldest transaction is to
be serviced.
NegatedDTI = 0b000 indicates that the MPC7400 must run the
data bus tenures in the same order as the address tenures
Timing Comments
Assertion/NegationSampled each cycle and qualiTed by a
qualiTed DBG in the following cycle.
8.4.6.3 Data Ready (DRDY)Output
The data ready (DRDY) signal is an output signal on the MPC7400 used in conjunction
with HIT to perform data intervention in MPX bus mode. Note that the L1_INTVEN and
L2_INTVEN Telds of MSSCR0 control the way that the MPC7400 uses data intervention
for the L1 and L2 caches. See Section 2.1.6, òMemory Subsystem Control Register
(MSSCR0).ó Also, see Section 9.6.2, òData Tenure in MPX Bus Mode,ó for more
information about the data intervention functionality. Following are the state meaning and
timing comments for the DRDY signal.