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Memory Management Unit (MMU)
Freescale Semiconductor
4-17
4.3.4
Effective Address Attribute Determination
The ColdFire core generates an effective memory address for all instruction fetches and data read and write
memory accesses. The previous ColdFire memory access control model was based strictly on physical
addresses. Every memory request address is a physical address analyzed by this memory access control
logic and assigned address attributes, including:
•
Cache mode
•
SRAM enable information
•
Write protect information
•
Write mode information
These attributes control processing of the memory request. The address itself is not affected by memory
access control logic.
Instruction and data references base effective address attributes and access mode on the instruction type
and the effective address. There are two types of accesses:
•
Special mode accesses, including interrupt acknowledges, reads/writes to program-visible control
registers (CACR, RAMBARs, and ACRs), cache-control commands (CPUSHL and INTOUCH),
and emulator-mode operations. These accesses have the following attributes:
— Non-cacheable
— Precise
— No write protection
Unless the CPU space/IACK mask bit is set, interrupt acknowledge cycles and emulator mode
operations are allowed to hit in RAMBAR. All other operations are normal mode accesses.
•
Normal mode accesses. For these accesses, an effective cache mode, precision, and
write-protection are calculated for each request.
For data, a normal mode access address is compared with the following priority, from highest to lowest:
RAMBAR, ACR0, and ACR1. If no match is found, default attributes in the CACR are used. The priority
for instruction accesses is RAMBAR, ACR2, and ACR3. Again, if no match is found, default CACR
attributes are used.
Only the test-and-set (TAS) instruction generates a normal mode access with implied cache mode and
precision. TAS is a special, byte-sized, read-modify-write instruction used in synchronization routines. A
TAS data access that does not hit in the RAMBAR is non-cacheable and precise. TAS uses the normal
effective write protection.
If the MMU is enabled, it adds two factors for calculating effective address attributes:
1101
Attempted read, read-modify-write of protected space (New for MMU)
1110
TLB miss on data read, or read-modify-write (New for MMU)
1111
OEP access error while executing in emulator mode (New for MMU)
Table 4-11. Fault Status Encodings (continued)
FS[3:0]
Definition
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...