Freescale Semiconductor MCF5480 - Manual (Page 177)

MMU Definition
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 5-11
5.5.3.2 MMU Memory Map
MMUBAR holds the base address for the 64-Kbyte MMU memory map, shown in Table 5-4 . The MMU
memory map area is not visible unless the MMUBAR is valid and must be referenced aligned. A large
portion of the map is reserved for future use.
The address space ID (ASID) is located in a CPU space control register. The 8-bit ASID value located in
the low order byte of a 32-bit supervisor control register, mapped into CPU space at address 0x003 and
accessed using a MOVEC instruction. The ColdFire Family Programmer’s Reference Manual describes
MOVEC.
This 8-bit field is the current user ASID. The ASID is an extension to the virtual address. Address space
0x00 may be reserved for supervisor mode. See address space mode functionality in Section 5.5.3.3,
“MMU Control Register (MMUCR) .” The other 255 address spaces are used to tag user processes. The
TLB entry ASID values are compared to this value for user mode unless the TLB entry is marked shared
(MMUTR[SG] is set). The TLB entry ASID value may be compared to 0x00 for supervisor accesses.
5.5.3.3 MMU Control Register (MMUCR)
MMUCR, Figure 5-4 , has the address space mode and virtual mode enable bits. The user must force
pipeline synchronization after writing to this register. Therefore, all writes to this register must be
immediately followed by a NOP instruction.
Table 5-3. MMUBAR Field Descriptions
Bits Name Description
31–16 BA Base address. Defines the base address for the 64-Kbyte address space mapped to the
MMU.
15–1 — Reserved, should be cleared. Writes are ignored and reads return zeros.
0 V Valid. Indicates when MMUMBAR contents are valid. BA is not used unless V is set.
0 MMUBAR contents are not valid.
1 MMUBAR contents are valid.
Table 5-4. MMU Memory Map
Offset from MMUBAR Name
+ 0x0000 MMU control register (MMUCR)
+ 0x0004 MMU operation register (MMUOR)
+ 0x0008 MMU status register (MMUSR)
+ 0x000C Reserved
+ 0x0010 MMU fault, test, or TLB address register (MMUAR)
+ 0x0014 MMU read/write TLB tag register (MMUTR)
+ 0x0018 MMU read/write TLB data register (MMUDR)
+ 0x001C–0xFFFC Reserved
1
1
May be used for implementation-specific information/control registers