MPC555
/
MPC556
L-BUS TO U-BUS INTERFACE (L2U)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
11-4
11.5 Data Memory Protection
The data memory protection unit (DMPU) in the L2U module provides access protec-
tion for the memory regions on the U-bus side from load/store accesses by the RCPU.
(Only U-bus space is protected.) The DMPU does not protect PowerPC register ac-
cesses initiated by the RCPU on the L-bus. The user can assign up to four regions of
access protection attributes and can assign global attributes to any space not included
in the active regions. When it detects an access violation, the L2U generates an ex-
ception request to the CPU.
Figure 11-2 DMP Basic Functional Diagram
11.5.1 Functional Description
Data memory protection is assigned on a regional basis. Default manipulation of the
DMPU is done on a global region. The DMPU has control registers which contain the
following information: region protection on/off, region base address, region size, and
the region’s access permissions. Each region’s protection attributes can be turned on/
off by configuring the enable attribute bit (ENRx) located in the global region attribute
register.
During each load/store access from the RCPU core to the U-bus, the address is com-
pared to the value in the region base address register of each enabled region. Any ac-
cess that matches the specific region within its appropriate size, as defined by the
region size field (RS) of the region attribute register, sets a match indication.
Region0 protection/attribute
Exception
Logic
Specific
Error Interrupts
Region
to Core
Address
Access attribute
Region1 protection/attribute
Region2 protection/attribute
Region3 protection/attribute
Global protection/attribute
ACCESS
Region0 Address and size
Region1 Address and size
Region2 Address and size
Region3 Address and size
GRANTED
Match
select
MSR
DR
Protection/Attribute
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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