SDCR, Secure Debug Control Register

The SDCR characteristics are:

Purpose

Provides EL3 configuration options for self-hosted debug, trace, and the Performance Monitors Extension.

Configuration

AArch32 System register SDCR bits [31:0] can be mapped to AArch64 System register MDCR_EL3[31:0] , but this is not architecturally mandated.

Some or all RW fields of this register have defined reset values. These apply whenever the register is accessible. This means they apply when the PE resets into EL3 using AArch32.

Attributes

SDCR is a 32-bit register.

Field descriptions

The SDCR bit assignments are:

Bits [31:24]

Reserved, RES0.

SCCD, bit [23]

When ARMv8.5-PMU is implemented:

Secure Cycle Counter Disable. Prohibits PMCCNTR from counting in Secure state.

This bit does not affect the CPU_CYCLES event or any other event that counts cycles.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

Reserved, RES0.

Bit [22]

Reserved, RES0.

EPMAD, bit [21]

When ARMv8.4-Debug is implemented and PMUv3 is implemented:

External debug interface Performance Monitors registers disable. This controls Non-secure access to Performance Monitors registers by an external debugger.

If the Performance Monitors Extension does not support external debug interface accesses this bit is RES0.

In a system where the PE resets into EL3, this field resets to 0.

When PMUv3 is implemented:

External debug interface Performance Monitors registers disable. This controls access to Performance Monitors registers by an external debugger.

If the Performance Monitors Extension does not support external debug interface accesses this bit is RES0.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

Reserved, RES0.

EDAD, bit [20]

When ARMv8.4-Debug is implemented:

External debug register Non-secure access disable. Controls access to debug registers by an external debugger.

In a system where the PE resets into EL3, this field resets to 0.

When ARMv8.2-Debug is implemented:

External debug access disable. This disables access to debug registers by an external debugger.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

External debug access disable. This disables access to debug registers by an external debugger.

In a system where the PE resets into EL3, this field resets to 0.

TTRF, bit [19]

When ARMv8.4-Trace is implemented:

Trap Trace Filter controls. Controls whether accesses at EL2 and EL1 to the trace filter control registers are trapped to EL3.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

Reserved, RES0.

STE, bit [18]

When ARMv8.4-Trace is implemented:

Secure Trace Enable. This bit enables tracing in Secure state and controls the level of authentication required by an external debugger to enable external tracing.

If EL3 is not implemented and the PE executes in Secure state, the PE behaves as if this bit is set to 1.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

Reserved, RES0.

SPME, bit [17]

When ARMv8.2-Debug is implemented and PMUv3 is implemented:

Secure Performance Monitors enable. This allows event counting in Secure state.

If EL3 is not implemented and the PE is executing in Secure state, then the Effective value of this bit is 0b1.

In a system where the PE resets into EL3, this field resets to 0.

When PMUv3 is implemented:

Secure Performance Monitors enable. This allows event counting in Secure state.

If EL3 is not implemented and the PE is executing in Secure state, then the Effective value of this bit is 0b1.

In a system where the PE resets into EL3, this field resets to 0.

Otherwise:

Reserved, RES0.

Bit [16]

Reserved, RES0.

SPD, bits [15:14]

AArch32 Secure privileged debug. Enables or disables debug exceptions from Secure state, other than Breakpoint Instruction exceptions. Valid values for this field are:

Other values are reserved, and have the CONSTRAINED UNPREDICTABLE behavior that they must have the same behavior as 0b00. Software must not rely on this property as the behavior of reserved values might change in a future revision of the architecture.

If debug exceptions from Secure EL1 are enabled, then debug exceptions from Secure EL0 are also enabled.

Otherwise, debug exceptions from Secure EL0 are enabled only if SDER32_EL3.SUIDEN == 1.

If EL3 is using AArch32, SDCR.SPD controls debug exceptions from EL3 and not from Secure EL1, as there is no Secure EL1.

Ignored in Non-secure state. Debug exceptions from Breakpoint Instruction exceptions are always enabled.

In a system where the PE resets into EL3, this field resets to 0.

Bits [13:0]

Reserved, RES0.

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif !ELUsingAArch32(EL2) && SCR_EL3.<NS,EEL2> == '01' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif !ELUsingAArch32(EL3) && SCR_EL3.NS == '0' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return SDCR;
              

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif !ELUsingAArch32(EL2) && SCR_EL3.<NS,EEL2> == '01' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif !ELUsingAArch32(EL3) && SCR_EL3.NS == '0' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' && CP15SDISABLE2 == HIGH then
        UNDEFINED;
    else
        SDCR = R[t];