TCR_EL3, Translation Control Register (EL3)

The TCR_EL3 characteristics are:

Purpose

The control register for stage 1 of the EL3 translation regime.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

TCR_EL3 is a 64-bit register.

Field descriptions

The TCR_EL3 bit assignments are:

Bits [63:32]

Reserved, RES0.

Bit [31]

Reserved, RES1.

TCMA, bit [30]

When ARMv8.5-MemTag is implemented:

Controls the generation of Unchecked accesses at EL3 when address [59:56] = 0b0000.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

TBID, bit [29]

When ARMv8.3-PAuth is implemented:

Controls the use of the top byte of instruction addresses for address matching.

This affects addresses where the address would be translated by tables pointed to by TTBR0_EL3.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HWU62, bit [28]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[62] of the stage 1 translation table Block or Page entry.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HWU61, bit [27]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[61] of the stage 1 translation table Block or Page entry.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HWU60, bit [26]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[60] of the stage 1 translation table Block or Page entry.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HWU59, bit [25]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[59] of the stage 1 translation table Block or Page entry.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HPD, bit [24]

When ARMv8.1-HPD is implemented:

Hierarchical Permission Disables. This affects the hierarchical control bits, APTable, PXNTable, and UXNTable, except NSTable, in the translation tables pointed to by TTBR0_EL3.

When disabled, the permissions are treated as if the bits are zero.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

Bit [23]

Reserved, RES1.

HD, bit [22]

When ARMv8.1-TTHM is implemented:

Hardware management of dirty state in stage 1 translations from EL3.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

HA, bit [21]

When ARMv8.1-TTHM is implemented:

Hardware Access flag update in stage 1 translations from EL3.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

TBI, bit [20]

Top Byte Ignored. Indicates whether the top byte of an address is used for address match for the TTBR0_EL3 region, or ignored and used for tagged addresses.

This affects addresses generated in EL3 using AArch64 where the address would be translated by tables pointed to by TTBR0_EL3. It has an effect whether the EL3 translation regime is enabled or not.

If ARMv8.3-PAuth is implemented and TCR_EL3.TBID is 1, then this field only applies to Data accesses.

Otherwise, if the value of TBI is 1, then bits[63:56] of that target address are also set to 0 before the address is stored in the PC, in the following cases:

• A branch or procedure return within EL3.
• A exception taken to EL3.
• An exception return to EL3.

For more information, see 'Address tagging in AArch64 state' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

This field resets to an architecturally UNKNOWN value.

Bit [19]

Reserved, RES0.

PS, bits [18:16]

Physical Address Size.

Other values are reserved.

The reserved values behave in the same way as the 0b101 or 0b110 encoding, but software must not rely on this property as the behavior of the reserved values might change in a future revision of the architecture.

The value 0b110 is permitted only if ARMv8.2-LPA is implemented and the translation granule size is 64KB.

In an implementation that supports 52-bit PAs, if the value of this field is not 0b110 or a value treated as 0b110, then bits[51:48] of every translation table base address for the stage of translation controlled by TCR_EL3 are 0b0000.

This field resets to an architecturally UNKNOWN value.

TG0, bits [15:14]

Granule size for the TTBR0_EL3.

Other values are reserved.

If the value is programmed to either a reserved value, or a size that has not been implemented, then the hardware will treat the field as if it has been programmed to an IMPLEMENTATION DEFINED choice of the sizes that has been implemented for all purposes other than the value read back from this register.

It is IMPLEMENTATION DEFINED whether the value read back is the value programmed or the value that corresponds to the size chosen.

This field resets to an architecturally UNKNOWN value.

SH0, bits [13:12]

Shareability attribute for memory associated with translation table walks using TTBR0_EL3.

Other values are reserved. The effect of programming this field to a Reserved value is that behavior is CONSTRAINED UNPREDICTABLE, as described in 'Reserved values in AArch64 System registers and translation table entries' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section K1.2.2.

This field resets to an architecturally UNKNOWN value.

ORGN0, bits [11:10]

Outer cacheability attribute for memory associated with translation table walks using TTBR0_EL3.

This field resets to an architecturally UNKNOWN value.

IRGN0, bits [9:8]

Inner cacheability attribute for memory associated with translation table walks using TTBR0_EL3.

This field resets to an architecturally UNKNOWN value.

Bits [7:6]

Reserved, RES0.

T0SZ, bits [5:0]

The size offset of the memory region addressed by TTBR0_EL3. The region size is 2^(64-T0SZ) bytes.

The maximum and minimum possible values for T0SZ depend on the level of translation table and the memory translation granule size, as described in the AArch64 Virtual Memory System Architecture chapter.

This field resets to an architecturally UNKNOWN value.

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return TCR_EL3;
              

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    TCR_EL3 = X[t];