TRBMAR_EL1
Trace Buffer Memory Attribute Register
TRBMAR_EL1 is in the Core power domain
when FEAT_TRBE_EXT is implemented
TRBE
0x028
TRBMAR_EL1
When DoubleLockStatus(), or !IsCorePowered(), or OSLockStatus(), or !AllowExternalTraceBufferAccess(addrdesc)
ERROR
RW
TRBMAR_EL1
Architectural
AArch64
63
0
63
0
63
0
63
0
Controls Trace Buffer Unit accesses to memory.
TRBE
TRBMAR_EL1 is a 64-bit register.
63
12
63:12
Reserved, RES0.
PAS
11
10
11:10
Physical address specifier. Defines the PAS attribute for memory addressed by the buffer in External mode.
All other values are reserved.
If the Trace Buffer Unit is using external mode and either TRBMAR_EL1.PAS is set to a reserved value, or the IMPLEMENTATION DEFINED authentication interface prohibits invasive debug of the Security state corresponding to the physical address space selected by TRBMAR_EL1.PAS, then when the Trace Buffer Unit receives trace data from the trace unit, it does not write the trace data to memory and generates a trace buffer management event. That is, if any of the following apply:
ExternalInvasiveDebugEnabled() == FALSE.
TRBMAR_EL1.PAS is 0b00, and either ExternalSecureInvasiveDebugEnabled() == FALSE or Secure state is not implemented.
TRBMAR_EL1.PAS is 0b10, and either ExternalRootInvasiveDebugEnabled() == FALSE or FEAT_RME is not implemented.
TRBMAR_EL1.PAS is 0b11, and either ExternalRealmInvasiveDebugEnabled() == FALSE or FEAT_RME is not implemented.
This field is ignored by the PE when SelfHostedTraceEnabled() == TRUE.
0b00
Secure.
When FEAT_Secure is implemented
0b01
Non-secure.
0b10
Root.
When FEAT_RME is implemented
0b11
Realm.
When FEAT_RME is implemented
AU
SH
9
8
9:8
Trace buffer stage 1 shareability domain. Defines the shareability domain for Normal memory used by the trace buffer.
All other values are reserved.
If the trace buffer pointers specify virtual addresses, the memory attributes are defined by the translation tables and this field is ignored.
This field is ignored when TRBMAR_EL1.Attr specifies any of the following memory types:
Any Device memory type.
Normal memory, Inner Non-cacheable, Outer Non-cacheable.
All Device and Normal Inner Non-cacheable Outer Non-cacheable memory regions are always treated as Outer Shareable.
0b00
Non-shareable.
0b10
Outer Shareable.
0b11
Inner Shareable.
AU
Attr
7
0
7:0
Trace buffer stage 1 memory type and attributes. Defines the memory type and, for Normal memory, the cacheability attributes, for memory addressed by the trace buffer.
The encoding of this field is the same as that of a MAIR_ELx.Attr<n> field, as follows:
AttrMeaning
0b0000dd00Device memory.
See encoding of 'dd' for the type of Device memory.
0b0000dd01If FEAT_XS is implemented:
Device memory with the XS attribute set to 0.
See encoding of 'dd' for the type of Device memory.
Otherwise,UNPREDICTABLE.
0b0000dd1xUNPREDICTABLE.
0booooiiiiwhere oooo != 0000
and iiii != 0000Normal memory. See encoding of 'oooo' and 'iiii' for the
type of Normal memory.
0b01000000If FEAT_XS is implemented:
Normal Inner Non-cacheable, Outer Non-cacheable memory
with the XS attribute set to 0.
Otherwise,UNPREDICTABLE.
0b10100000If FEAT_XS is implemented:
Normal Inner Write-through Cacheable, Outer Write-through Cacheable,
Read-Allocate, No-Write Allocate, Non-transient memory
with the XS attribute set to 0.
Otherwise,UNPREDICTABLE.
0b11110000If FEAT_MTE2 is implemented:
Tagged Normal Inner Write-Back, Outer Write-Back,
Read-Allocate, Write-Allocate Non-transient memory.
Otherwise,UNPREDICTABLE.
0bxxxx0000where xxxx != 0000
and xxxx != 0100
and xxxx != 1010
and xxxx != 1111UNPREDICTABLE.
dd is encoded as follows:
'dd'Meaning
0b00Device-nGnRnE memory.
0b01Device-nGnRE memory.
0b10Device-nGRE memory.
0b11Device-GRE memory.
oooo is encoded as follows:
'oooo'Meaning
0b0000See encoding of Attr.
0b00RWwhere RW != 00Normal memory, Outer Write-Through Transient.
0b0100Normal memory, Outer Non-cacheable.
0b01RWwhere RW != 00Normal memory, Outer Write-Back Transient.
0b10RWNormal memory, Outer Write-Through Non-transient.
0b11RWNormal memory, Outer Write-Back Non-transient.
R encodes the Outer Read-Allocate policy and W encodes the Outer Write-Allocate policy.
iiii is encoded as follows:
'iiii'Meaning
0b0000See encoding of Attr.
0b00RWwhere RW != 00Normal memory, Inner Write-Through Transient.
0b0100Normal memory, Inner Non-cacheable.
0b01RWwhere RW != 00Normal memory, Inner Write-Back Transient.
0b10RWNormal memory, Inner Write-Through Non-transient.
0b11RWNormal memory, Inner Write-Back Non-transient.
R encodes the Inner Read-Allocate policy and W encodes the Inner Write-Allocate policy.
In oooo and iiii, R and W are encoded as follows:
'R' or 'W'Meaning
0b0No Allocate.
0b1Allocate.
When FEAT_XS is implemented, stage 1 Inner Write-Back Cacheable, Outer Write-Back Cacheable memory types have the XS attribute set to 0.
If the trace buffer pointers specify virtual addresses, the memory attributes are defined by the translation tables and this field is ignored.
AU
The PE might ignore a write to TRBMAR_EL1 if any of the following apply:
TRBLIMITR_EL1.E is 1 and the Trace Buffer Unit is using Self-hosted mode.
TRBLIMITR_EL1.XE is 1 and the Trace Buffer Unit is using External mode.
2026-03-26 20:27:25
2026-03_rel