Arm® A64 Instruction Set Architecture: Armv8, for Armv8-A architecture profile

Library pseudocode for shared/debug/breakpoint/CheckValidStateMatch

// CheckValidStateMatch()
// ======================
// Checks for an invalid state match that will generate Constrained Unpredictable behaviour, otherwise
// returns Constraint_NONE.

(Constraint, bits(2), bit, bits(2)) CheckValidStateMatch(bits(2) SSC, bit HMC, bits(2) PxC, boolean isbreakpnt)
    boolean reserved = FALSE;

    // Match 'Usr/Sys/Svc' only valid for AArch32 breakpoints
    if (!isbreakpnt || !HaveAArch32EL(EL1)) && HMC:PxC == '000' && SSC != '11' then
        reserved = TRUE;

    // Both EL3 and EL2 are not implemented
    if !HaveEL(EL3) && !HaveEL(EL2) && (HMC != '0' || SSC != '00') then
        reserved = TRUE;

    // EL3 is not implemented
    if !HaveEL(EL3) && SSC IN {'01','10'} && HMC:SSC:PxC != '10100' then
        reserved = TRUE;

    // EL3 using AArch64 only
    if (!HaveEL(EL3) || HighestELUsingAArch32()) && HMC:SSC:PxC == '11000' then
        reserved = TRUE;

    // EL2 is not implemented
    if !HaveEL(EL2) && HMC:SSC:PxC == '11100' then
        reserved = TRUE;

    // Secure EL2 is not implemented
    if !HaveSecureEL2Ext() && (HMC:SSC:PxC)  IN {'01100','10100','x11x1'} then
        reserved = TRUE;

    // Values that are not allocated in any architecture version
    if (HMC:SSC:PxC) IN {'01110','100x0','10110','11x10'} then
        reserved = TRUE;

    if reserved then
        // If parameters are set to a reserved type, behaves as either disabled or a defined type
        (c, <HMC,SSC,PxC>) = ConstrainUnpredictableBits(Unpredictable_RESBPWPCTRL);
        assert c IN {Constraint_DISABLED, Constraint_UNKNOWN};
        if c == Constraint_DISABLED then
            return (c, bits(2) UNKNOWN, bit UNKNOWN, bits(2) UNKNOWN);
        // Otherwise the value returned by ConstrainUnpredictableBits must be a not-reserved value

    return (Constraint_NONE, SSC, HMC, PxC);