ARM1176JZF-S Technical Reference Manual: 3.2.25. c9, Data TCM Region Register

3.2.25. c9, Data TCM Region Register

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

The Data TCM Region Register is:

in CP15 c9
a 32-bit read/write register common to Secure and Non-secure worlds
accessible in privileged modes only.

If the processor is configured to have 2 Data TCMs, each TCM has a separate Data TCM Region Register. The TCM Selection Register determines the register in use.

Figure 3.50 shows the bit arrangement for the Data TCM Region Register.

Figure 3.50. Data TCM Region Register format

Table 3.85 lists how the bit values correspond with the Data TCM Region Register functions.

Table 3.85. Data TCM Region Register bit functions

Bits	Field name	Function
[31:12]	Base address	Contains 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]	Size	Indicates the size of the TCM on reads^[a]. All other values are reserved: b00000 = 0KB b00011 = 4KB b00100 = 8KB b00101 = 16KB b00110 = 32KB.
[1]	-	UNP/SBZ.
[0]	En	Indicates if the TCM is enabled. 0 = TCM disabled, reset value 1 = TCM enabled.
^[a]On writes this field is ignored. For more details see Tightly-coupled memory.

Attempts to write to this register in Secure Privileged mode when CP15SDISABLE is HIGH result in an Undefined exception, see TrustZone write access disable.

Note

When the NS access bit is 0 for Data TCM, see c9, Data TCM Non-secure Control Access Register, attempts to access the Data TCM Region Register from the Non-secure world cause an Undefined exception.

Table 3.86 lists the results of attempted access for each mode.

Table 3.86. Results of access to the Data TCM Region Register

NS access bit value	Secure Privileged		Non-secure Privileged		User
NS access bit value	Read	Write	Read	Write	User
0	Data	Data	Undefined exception	Undefined exception	Undefined exception
1	Data	Data	Data	Data	Undefined exception

To use the Data TCM Region Register read or write CP15 with:

Opcode_1 set to 0
CRn set to c9
CRm set to c1
Opcode_2 set to 0.

For example:

MRC p15, 0, <Rd>, c9, c1, 0    ; Read Data TCM Region Register

MCR p15, 0, <Rd>, c9, c1, 0    ; Write Data TCM Region Register

Attempting to change the Data TCM Region Register while a DMA operation is running has Unpredictable effects but there is no impact on security.

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