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3.3.21. c9, Instruction TCM Region Register

The purpose of the Instruction TCM Region Register is to describe the physical base address and size of the Instruction TCM region and to provide a mechanism to enable it.

The Instruction TCM Region Register is:

  • in CP15 c9

  • a 32-bit read/write register

  • accessible in privileged mode only.

Note

ARM1136JF-S processors have a single TCM on each side, Data and Instruction. See c9, Data TCM Region Register for details of configuring the Data TCM region.

Figure 3.47 shows the arrangement of bits in the Instruction TCM Region Register.

Figure 3.47. Instruction TCM Region Register format

Figure 3.47. Instruction TCM Region Register format

Table 3.96 shows the bit functions of the Instruction TCM Region Register.

Table 3.96. Instruction TCM Region Register bit functions

Bit range

Field name

Function

[31:12]

Base address

The physical base address of the TCM. The base address must be aligned to the size of the TCM. Any bits in the range [(log2(RAMSize)-1):12] are ignored.

The base address is 0 at Reset.

[11:7]-UNP/SBZ.
[6:2]SizeOn reads, the Size field indicates the size of the TCM, see Table 3.97.[a]
[1]SC

Indicates if the TCM is enabled as SmartCache:

0 = Local RAM. This is the reset value.

1 = SmartCache.

[0]

En

The En bit indicates if the TCM is enabled:

0 = TCM disabled. This is the reset value.

1 = TCM enabled.

On reset, the value of the TCM enable bit is determined by the pin INITRAM:

  • INITRAM LOW sets En to 0

  • INITRAM HIGH sets En to 1.[b]

[a] On writes this field is ignored. For more details see Tightly-coupled memory.

[b] When INITRAM is HIGH the Instruction TCM is enabled directly from reset, with a Base address of 0x00000. When the processor comes out of reset, it executes the instructions in the Instruction TCM instead of fetching instructions from external memory, except when the processor uses high vectors.


Table 3.97 shows the Size field encoding value for each memory size. All other values are reserved.

Table 3.97. Size field encoding for Instruction TCM Region Register
Size fieldMemory size
b000000KB
b000114KB
b001008KB
b0010116KB
b0011032KB
b0011164KB

Accessing the Instruction TCM Region Register

Table 3.98 shows the results of attempted accesses to the Instruction TCM Region Register for each mode.

Table 3.98. Results of accesses to the Instruction TCM Region Register
Privileged readPrivileged writeUser read or write
Data readData writeUndefined Instruction exception

To access the Instruction TCM Region Register you read or write CP15 with:

  • Opcode_1 set to 0

  • CRn set to c9

  • CRm set to c1

  • Opcode_2 set to 1.

For example:

MRC p15, 0, <Rd>, c9, c1, 1            ; Read Instruction TCM Region Register
MCR p15, 0, <Rd>, c9, c1, 1            ; Write Instruction TCM Region Register

Changing the Instruction TCM Region Register while a Prefetch Range or DMA operation is running has Unpredictable effects.