TRBIDR_EL1, Trace Buffer ID Register

The TRBIDR_EL1 characteristics are:

Purpose

Describes constraints on using the Trace Buffer Unit to software, including whether the Trace Buffer Unit can be programmed at the current Exception level.

Configuration

This register is present only when FEAT_TRBE is implemented. Otherwise, direct accesses to TRBIDR_EL1 are UNDEFINED.

Attributes

TRBIDR_EL1 is a 64-bit register.

Field descriptions

The TRBIDR_EL1 bit assignments are:

Bits [63:6]

Reserved, RES0.

F, bit [5]

Flag Updates. Defines whether the address translation performed by the Trace Buffer Unit manages the Access Flag and dirty state. Defined values are:

P, bit [4]

Programming not allowed. The trace buffer is owned by a higher Exception level or by the other Security state. Defined values are:

The value read from this field depends on the current Exception level and the values of MDCR_EL3.NSTB and MDCR_EL2.E2TB:

• If EL3 is implemented and either MDCR_EL3.NSTB == 0b00 or MDCR_EL3.NSTB == 0b01, meaning the owning Security state is Secure state, this bit reads as one from:
  • Non-secure EL2.
  • Non-secure EL1.
  • If Secure EL2 is implemented and enabled, and MDCR_EL2.E2TB == 0b00, Secure EL1.
• If EL3 is implemented and either MDCR_EL3.NSTB == 0b10 or MDCR_EL3.NSTB == 0b11, meaning the owning Security state is Non-secure state, this bit reads as one from:
  • Secure EL1.
  • If Secure EL2 is implemented, Secure EL2.
  • If EL2 is implemented and MDCR_EL2.E2TB == 0b00, Non-secure EL1.
• If EL3 is not implemented, EL2 is implemented, and MDCR_EL2.E2TB == 0b00, this bit reads as one from EL1.
• Otherwise, this bit reads as zero.

Align, bits [3:0]

Defines the minimum alignment constraint for writes to TRBPTR_EL1 and TRBTRG_EL1. Defined values are:

All other values are reserved.

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HDFGRTR_EL2.TRBIDR_EL1 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        return TRBIDR_EL1;
elsif PSTATE.EL == EL2 then
    return TRBIDR_EL1;
elsif PSTATE.EL == EL3 then
    return TRBIDR_EL1;