dcps1

Debug Change PE State to EL1 (A32)

DCPS1

Switches execution to EL1 (Debug).

Details

Changes PE execution state to EL1 for debugging purposes. This is an A32-only instruction that immediately changes exception level and may update execution state; it does not return (implicit branch to debug handler). Condition flags are not affected by the instruction itself but are context-switched at the target exception level.

Pseudocode Operation

DebugChangeEL(EL1); // Changes exception level and branches to debug handler

Example

DCPS1

Encoding

Binary Layout

111101111000

1111

1000

0000000000

Format System

Opcode 0xF78F8001

Extension A32 (System)

Operands

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xF78F8001	DCPS1		T32		111101111000 \| 1111 \| 1000 \| 0000000000 \| 01

Description

Debug Change PE State to EL1 allows the debugger to move the PE into EL1 from EL0 or to a specific mode at the current Exception level. DCPS1 is undefined if any of: When the PE executes DCPS1 at EL0, EL1 or EL3: When the PE executes DCPS1 at EL2 the PE does not change mode, and ELR_hyp, HSR, SPSR_hyp, DLR and DSPSR become UNKNOWN. For more information on the operation of the DCPS<n> instructions, see DCPS.

Operation

if !Halted() then UNDEFINED;

if EL2Enabled() && PSTATE.EL == EL0 then
    tge = if ELUsingAArch32(EL2) then HCR.TGE else HCR_EL2.TGE;
    if tge == '1' then UNDEFINED;

if PSTATE.EL != EL0 || ELUsingAArch32(EL1) then
    if PSTATE.M == M32_Monitor then SCR.NS = '0';
    if PSTATE.EL != EL2 then
        AArch32.WriteMode(M32_Svc);
        PSTATE.E = SCTLR.EE;
        if HavePANExt() && SCTLR.SPAN == '0' then PSTATE.PAN = '1';
        LR_svc = bits(32) UNKNOWN;
        SPSR_svc = bits(32) UNKNOWN;
    else
        PSTATE.E = HSCTLR.EE;
        ELR_hyp = bits(32) UNKNOWN;
        HSR = bits(32) UNKNOWN;
        SPSR_hyp = bits(32) UNKNOWN;

    DLR = bits(32) UNKNOWN;
    DSPSR = bits(32) UNKNOWN;
else                                        // Targeting EL1 using AArch64
    AArch64.MaybeZeroRegisterUppers();
    MaybeZeroSVEUppers(EL1);
    PSTATE.nRW = '0';
    PSTATE.SP = '1';
    PSTATE.EL = EL1;
    if HavePANExt() && SCTLR_EL1.SPAN == '0' then PSTATE.PAN = '1';
    if HaveUAOExt() then PSTATE.UAO = '0';

    ELR_EL1 = bits(64) UNKNOWN;
    ESR_EL1 = bits(64) UNKNOWN;
    SPSR_EL1 = bits(64) UNKNOWN;

    DLR_EL0 = bits(64) UNKNOWN;
    DSPSR_EL0 = bits(64) UNKNOWN;

    // SCTLR_EL1.IESB might be ignored in Debug state.
    if (HaveIESB() && SCTLR_EL1.IESB == '1' &&
          !ConstrainUnpredictableBool(Unpredictable_IESBinDebug)) then
        SynchronizeErrors();

UpdateEDSCRFields();                        // Update EDSCR PE state flags