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# TCO, Tag Check Override

The TCO characteristics are:

## Purpose

When ARMv8.5-MemTag is implemented, this register allows tag checks to be disabled globally.

## Configuration

This register is present only when ARMv8.5-MemTag is implemented. Otherwise, direct accesses to TCO are UNDEFINED.

## Attributes

TCO is a 64-bit register.

## Field descriptions

The TCO bit assignments are:

63 | 62 | 61 | 60 | 59 | 58 | 57 | 56 | 55 | 54 | 53 | 52 | 51 | 50 | 49 | 48 | 47 | 46 | 45 | 44 | 43 | 42 | 41 | 40 | 39 | 38 | 37 | 36 | 35 | 34 | 33 | 32
RES0
RES0 | TCO | RES0
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0

#### Bits [63:26]

Reserved, RES0.

#### TCO, bit [25]
From Armv8.5:

Allows memory tag checks to be globally disabled.

TCO | Meaning
--- | ---
0b0 | Loads and Stores are not affected by this control.
0b1 | Loads and Stores are unchecked.

####
Otherwise:

Reserved, RES0.

#### Bits [24:0]

Reserved, RES0.

## Accessing the TCO

For details on the operation of the MSR (immediate) accessor, see MSR (immediate).

Accesses to this register use the following encodings:

#### MRS <Xt>, TCO

op0 | op1 | CRn | CRm | op2
--- | --- | --- | --- | ---
0b11 | 0b011 | 0b0100 | 0b0010 | 0b111

if PSTATE.EL == EL0 then return Zeros(38):PSTATE.TCO:Zeros(25); elsif PSTATE.EL == EL1 then return Zeros(38):PSTATE.TCO:Zeros(25); elsif PSTATE.EL == EL2 then return Zeros(38):PSTATE.TCO:Zeros(25); elsif PSTATE.EL == EL3 then return Zeros(38):PSTATE.TCO:Zeros(25);

#### MSR TCO, <Xt>

op0 | op1 | CRn | CRm | op2
--- | --- | --- | --- | ---
0b11 | 0b011 | 0b0100 | 0b0010 | 0b111

if PSTATE.EL == EL0 then PSTATE.TCO = X[t]<25>; elsif PSTATE.EL == EL1 then PSTATE.TCO = X[t]<25>; elsif PSTATE.EL == EL2 then PSTATE.TCO = X[t]<25>; elsif PSTATE.EL == EL3 then PSTATE.TCO = X[t]<25>;

#### MSR TCO, #<imm>

op0 | op1 | CRn | op2
--- | --- | --- | ---
0b00 | 0b011 | 0b0100 | 0b100

AArch32 Registers | AArch64 Registers | AArch32 Instructions | AArch64 Instructions | Index by Encoding | External Registers | External Registers by Offset | Registers by Functional Group | Proprietary Notice

15/04/2019 16:47; 8c23526ba8a13a72aada4137daf3e3977b49036e

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