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TTBR0 has a specific format when using the Long-descriptor translation table format. TTBCR.EAE determines which format of the register is in use.
The following figure shows the TTBR0 bit assignments when TTBCR.EAE is 1.
An ASID for the translation table base address. The TTBCR.A1 field selects either TTBR0.ASID or TTBR1.ASID.
Translation table base address, bits[47:x]. Bits [x-1:0] are res0.
x is based on the value of TTBCR.T0SZ, and is calculated as follows:
The value of x determines the required alignment of the translation table, that must be aligned to 2x bytes.
If bits [x-1:3] are not all zero, this is a misaligned Translation Table Base Address. Its effects are constrained unpredictable, where bits [x-1:0] are treated as if all the bits are zero. The value read back from those bits is the value written.
To access the TTBR0 when TTBCR.EAE==1:
MRRC p15,0,<Rt>,<Rt2>,c2 ; Read 64-bit TTBR0 into Rt (low word) and Rt2 (high word) MCRR p15,0,<Rt>,<Rt2>,c2 ; Write Rt (low word) and Rt2 (high word) to 64-bit TTBR0
Register access is encoded as follows:
Table B1-95 TTBR0 access encoding