L-Bus to U-Bus Interface (L2U)
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
11-7
NOTE
The appropriate DMPU registers must be programmed before the MSR[DR]
bit is set. Otherwise, DMPU operation is not guaranteed.
Program the region base address in the L2U_RBAx registers to the lower boundary of the region specified
by the corresponding L2U_RAx[RS] field. If the region base address does not correspond to the boundary
of the block size programmed in the L2U_RAx, the DMPU snaps the region base to the lower boundary
of that block. For example, if the block size is programmed to 16 Kbytes for region zero (i.e.,
L2U_RA0[RS] = 0x3) and the region base address is programmed to 0x1FFF(i.e., L2U_RBA0[RBA] =
0x1), then the effective base address of region zero is 0x0. See
.
Figure 11-3. Region Base Address Example
External action is required to program only legal region sizes. The L2U does not check whether the value
is legal. If an illegal region size is programmed, the region calculation may not be successful.
11.5.3
L-Bus Memory Access Violations
All L-bus slaves have their own access protection logic. For consistency, all storage access violations have
the same termination result. Thus access violations for load/store accesses started by the RCPU always
have the same termination from all slaves: assertion of the data storage exception. All other L-bus masters
cause machine check exceptions.
11.6
Reservation Support
In general terms, a reservation activity is the process whereby a load and store instruction pair is
accompanied by a reservation of the data, the goal being to achieve an atomic operation. If a bus master
other than the one holding the reservation accesses the data (or some other specific condition occurs as
described in
Section 11.6.1, “Reservation Protocol
”) the reservation is lost and is indicated accordingly.
The RCPU storage reservation protocol supports a multi-level bus structure. For each local bus, storage
reservation is handled by the local reservation logic. The protocol tries to optimize reservation cancellation
such that an MPC500 processor (RCPU) is notified of storage reservation loss on a remote bus (U-bus,
IMB or external bus) only when it has issued a stwcx cycle to that address. That is, the reservation loss
indication comes as part of the stwcx cycle.
Region 0
(16 Kbytes)
Actual Programmed Region
Resulting Region
0x0000 0000
0x0000 1FFF
0x0000 3FFF
0x0000 5FFF
Summary of Contents for MPC561
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