4.3.24. c9, ATCM Region Register

The ATCM Region Register characteristics are:

  • Holds the base address and size of the ATCM.

  • Determines if the ATCM is enabled.

Usage constraints

The ATCM Region Register is:

  • a read/write register

  • accessible in Privileged mode only.


Available in all processor configurations.


Figure 4.42 shows the ATCM Region Register bit assignments.

Figure 4.42. ATCM Region Register bit assignments

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Table 4.44 shows the ATCM Region Register bit assignments.

Table 4.44. ATCM Region Register bit assignments





Base address

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

At reset, if LOCZRAMAm is set to:

0 = The initial base address is implementation-defined. See Configurable options

1 = The initial base address is 0x0.

[11:7]-UNP on reads, SBZ on writes.
[6:2]SizeSize. Indicates the size of the ATCM on reads. On writes this field is ignored. See About the TCMs.

b00000 = 0KB, no TCM

b00011 = 4KB

b00100 = 8KB

b00101 = 16KB

b00110 = 32KB

b00111 = 64KB

b01000 = 128KB

b01001 = 256KB

b01010 = 512kB

b01011 = 1MB

b01100 = 2MB

b01101 = 4MB

b01110 = 8MB.




Enables or disables the ATCM.

0 = Disabled.

1 = Enabled. The reset value of this field is determined by the INITRAMAm input pin.

This bit is RAZ if the processor has been implemented or integrated without an ATCM.

To access the ATCM Region Register, read or write CP15 with:

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