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DFSR, Data Fault Status Register

The DFSR characteristics are:

Purpose

Holds status information about the last data fault.

Configuration

AArch32 System register DFSR bits [31:0] are architecturally mapped to AArch64 System register ESR_EL1[31:0] .

This register is present only when AArch32 is supported at any Exception level. Otherwise, direct accesses to DFSR are UNKNOWN.

The current translation table format determines which format of the register is used.

Attributes

DFSR is a 32-bit register.

Field descriptions

The DFSR bit assignments are:

When TTBCR.EAE == 0:
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RES0 FnV AET CM ExT WnR FS[4] LPAE RES0 Domain FS[3:0]

Bits [31:17]

Reserved, RES0.

FnV, bit [16]

FAR not Valid, for a synchronous External abort other than a synchronous External abort on a translation table walk.

FnV	Meaning
0b0	DFAR is valid.
0b1	DFAR is not valid, and holds an UNKNOWN value.

This field is only valid for a synchronous External abort other than a synchronous External abort on a translation table walk. It is RES0 for all other Data Abort exceptions.

This field resets to an architecturally UNKNOWN value.

AET, bits [15:14]

When RAS is implemented:

Asynchronous Error Type. When DFSC is 0b010001, describes the PE error state after taking an asynchronous Data Abort exception. Possible values are:

AET	Meaning
0b00	Uncontainable (UC).
0b01	Unrecoverable state (UEU).
0b10	Restartable state (UEO).
0b11	Recoverable state (UER).

This field is valid only if the DFSC code is 0b010001. It is RES0 for all other aborts.

In the event of multiple errors taken as a single SError interrupt exception, the overall PE error state is reported.

Note

Software can use this information to determine what recovery might be possible. The recovery software must also examine any implemented fault records to determine the location and extent of the error.

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

CM, bit [13]

Cache maintenance fault. For synchronous faults, this bit indicates whether a cache maintenance instruction generated the fault. The possible values of this bit are:

CM	Meaning
0b0	Abort not caused by execution of a cache maintenance instruction.
0b1	Abort caused by execution of a cache maintenance instruction, or on an address translation.

On a synchronous Data Abort on a translation table walk, this bit is UNKNOWN.

On an asynchronous fault, this bit is UNKNOWN.

This field resets to an architecturally UNKNOWN value.

ExT, bit [12]

External abort type. This bit can be used to provide an IMPLEMENTATION DEFINED classification of External aborts.

In an implementation that does not provide any classification of External aborts, this bit is RES0.

For aborts other than External aborts this bit always returns 0.

This field resets to an architecturally UNKNOWN value.

WnR, bit [11]

Write not Read bit. Indicates whether the abort was caused by a write or a read instruction. The possible values of this bit are:

WnR	Meaning
0b0	Abort caused by a read instruction.
0b1	Abort caused by a write instruction.

For faults on the cache maintenance and address translation System instructions in the (coproc==0b1111) encoding space this bit always returns a value of 1.

This field resets to an architecturally UNKNOWN value.

FS[4], bit [10]

This field is bit[4] of FS[4:0].

Fault status bits. Possible values of FS[4:0] are:

FS	Meaning	Applies when
0b00001	Alignment fault.
0b00010	Debug exception.
0b00011	Access flag fault, level 1.
0b00100	Fault on instruction cache maintenance.
0b00101	Translation fault, level 1.
0b00110	Access flag fault, level 2.
0b00111	Translation fault, level 2.
0b01000	Synchronous External abort, not on translation table walk.
0b01001	Domain fault, level 1.
0b01011	Domain fault, level 2.
0b01100	Synchronous External abort, on translation table walk, level 1.
0b01101	Permission fault, level 1.
0b01110	Synchronous External abort, on translation table walk, level 2.
0b01111	Permission fault, level 2.
0b10000	TLB conflict abort.
0b10100	IMPLEMENTATION DEFINED fault (Lockdown fault).
0b10101	IMPLEMENTATION DEFINED fault (Unsupported Exclusive access fault).
0b10110	SError interrupt.
0b11000	SError interrupt, from a parity or ECC error on memory access.	When RAS is not implemented
0b11001	Synchronous parity or ECC error on memory access, not on translation table walk.	When RAS is not implemented
0b11100	Synchronous parity or ECC error on translation table walk, level 1.	When RAS is not implemented
0b11110	Synchronous parity or ECC error on translation table walk, level 2.	When RAS is not implemented

All other values are reserved.

For more information about the lookup level associated with a fault, see 'The level associated with MMU faults on a Short-descriptor translation table lookup'.

The FS field is split as follows:

FS[4] is DFSR[10].
FS[3:0] is DFSR[3:0].

This field resets to an architecturally UNKNOWN value.

LPAE, bit [9]

On taking a Data Abort exception, this bit is set as follows:

LPAE	Meaning
0b0	Using the Short-descriptor translation table formats.
0b1	Using the Long-descriptor translation table formats.

Hardware does not interpret this bit to determine the behavior of the memory system, and therefore software can set this bit to 0 or 1 without affecting operation.

This field resets to an architecturally UNKNOWN value.

Bit [8]

Reserved, RES0.

Domain, bits [7:4]

The domain of the fault address.

Arm deprecates any use of this field, see 'The Domain field in the DFSR'.

This field is UNKNOWN for certain faults where the DFSR is updated and reported using the Short-descriptor FSR encodings, see 'Validity of Domain field on faults that update the DFSR when using the Short-descriptor encodings'.

This field resets to an architecturally UNKNOWN value.

FS[3:0], bits [3:0]

This field is bits[3:0] of FS[4:0].

See FS[4] for the field description.

When TTBCR.EAE == 1:
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RES0 FnV AET CM ExT WnR RES0 LPAE RES0 STATUS

Bits [31:17]

Reserved, RES0.

FnV, bit [16]

FAR not Valid, for a synchronous External abort other than a synchronous External abort on a translation table walk.

FnV	Meaning
0b0	DFAR is valid.
0b1	DFAR is not valid, and holds an UNKNOWN value.

This field is only valid for a synchronous External abort other than a synchronous External abort on a translation table walk. It is RES0 for all other Data Abort exceptions.

This field resets to an architecturally UNKNOWN value.

AET, bits [15:14]

When RAS is implemented:

Asynchronous Error Type. This field describes the state of the PE after taking an asynchronous Data Abort exception.

AET	Meaning
0b00	Uncontainable error (UC) or uncategorized.
0b01	Unrecoverable error (UEU).
0b10	Restartable error (UEO) or Corrected error (CE).
0b11	Recoverable error (UER).

On a synchronous Data Abort, this field is RES0.

Note

Armv8.2 requires the implementation of the RAS Extension.

In the event of multiple errors taken as a single SError interrupt exception, the overall state of the PE is reported.

Note

This field resets to an architecturally UNKNOWN value.

Otherwise:

Reserved, RES0.

CM, bit [13]

Cache maintenance fault. For synchronous faults, this bit indicates whether a cache maintenance instruction generated the fault. The possible values of this bit are:

CM	Meaning
0b0	Abort not caused by execution of a cache maintenance instruction.
0b1	Abort caused by execution of a cache maintenance instruction.

On a synchronous Data Abort on a translation table walk, this bit is UNKNOWN.

On an asynchronous fault, this bit is UNKNOWN.

This field resets to an architecturally UNKNOWN value.

ExT, bit [12]

External abort type. This bit can be used to provide an IMPLEMENTATION DEFINED classification of External aborts.

In an implementation that does not provide any classification of External aborts, this bit is RES0.

For aborts other than External aborts this bit always returns 0.

This field resets to an architecturally UNKNOWN value.

WnR, bit [11]

Write not Read bit. Indicates whether the abort was caused by a write or a read instruction. The possible values of this bit are:

WnR	Meaning
0b0	Abort caused by a read instruction.
0b1	Abort caused by a write instruction.

For faults on the cache maintenance and address translation System instructions in the (coproc==0b1111) encoding space this bit always returns a value of 1.

This field resets to an architecturally UNKNOWN value.

Bit [10]

Reserved, RES0.

LPAE, bit [9]

On taking a Data Abort exception, this bit is set as follows:

LPAE	Meaning
0b0	Using the Short-descriptor translation table formats.
0b1	Using the Long-descriptor translation table formats.

Hardware does not interpret this bit to determine the behavior of the memory system, and therefore software can set this bit to 0 or 1 without affecting operation.

This field resets to an architecturally UNKNOWN value.

Bits [8:6]

Reserved, RES0.

STATUS, bits [5:0]

Fault status bits. Possible values of this field are:

STATUS	Meaning	Applies when
0b000000	Address size fault in translation table base register.
0b000001	Address size fault, level 1.
0b000010	Address size fault, level 2.
0b000011	Address size fault, level 3.
0b000101	Translation fault, level 1.
0b000110	Translation fault, level 2.
0b000111	Translation fault, level 3.
0b001001	Access flag fault, level 1.
0b001010	Access flag fault, level 2.
0b001011	Access flag fault, level 3.
0b001101	Permission fault, level 1.
0b001110	Permission fault, level 2.
0b001111	Permission fault, level 3.
0b010000	Synchronous External abort, not on translation table walk.
0b010001	Asynchronous SError interrupt.
0b010101	Synchronous External abort, on translation table walk, level 1.
0b010110	Synchronous External abort, on translation table walk, level 2.
0b010111	Synchronous External abort, on translation table walk, level 3.
0b011000	Synchronous parity or ECC error on memory access, not on translation table walk.	When RAS is not implemented
0b011001	Asynchronous SError interrupt, from a parity or ECC error on memory access.	When RAS is not implemented
0b011101	Synchronous parity or ECC error on memory access on translation table walk, level 1.	When RAS is not implemented
0b011110	Synchronous parity or ECC error on memory access on translation table walk, level 2.	When RAS is not implemented
0b011111	Synchronous parity or ECC error on memory access on translation table walk, level 3.	When RAS is not implemented
0b100001	Alignment fault.
0b100010	Debug exception.
0b110000	TLB conflict abort.
0b110100	IMPLEMENTATION DEFINED fault (Lockdown).
0b110101	IMPLEMENTATION DEFINED fault (Unsupported Exclusive access).

All other values are reserved.

For more information about the lookup level associated with a fault, see 'The level associated with MMU faults on a Long-descriptor translation table lookup'.

This field resets to an architecturally UNKNOWN value.

Accessing the DFSR

Accesses to this register use the following encodings:

MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc	opc1	CRn	CRm	opc2
0b1111	0b000	0b0101	0b0000	0b000

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T5 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T5 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TRVM == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TRVM == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) then
        return DFSR_NS;
    else
        return DFSR;
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && ELUsingAArch32(EL3) then
        return DFSR_NS;
    else
        return DFSR;
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        return DFSR_S;
    else
        return DFSR_NS;

MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc	opc1	CRn	CRm	opc2
0b1111	0b000	0b0101	0b0000	0b000

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T5 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T5 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TVM == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TVM == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) then
        DFSR_NS = R[t];
    else
        DFSR = R[t];
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && ELUsingAArch32(EL3) then
        DFSR_NS = R[t];
    else
        DFSR = R[t];
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        DFSR_S = R[t];
    else
        DFSR_NS = R[t];

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31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0															FnV	AET		CM	ExT	WnR	FS[4]	LPAE	RES0	Domain				FS[3:0]

Arm® Architecture Registers Armv8, for Armv8-A architecture profile

DFSR, Data Fault Status Register

Purpose

Configuration

Attributes

Field descriptions

When TTBCR.EAE == 0:313029282726252423222120191817161514131211109876543210RES0FnVAETCMExTWnRFS[4]LPAERES0DomainFS[3:0]

Bits [31:17]

FnV, bit [16]

AET, bits [15:14] When RAS is implemented:

Otherwise:

CM, bit [13]

ExT, bit [12]

WnR, bit [11]

FS[4], bit [10]

LPAE, bit [9]

Bit [8]

Domain, bits [7:4]

FS[3:0], bits [3:0]

When TTBCR.EAE == 1:313029282726252423222120191817161514131211109876543210RES0FnVAETCMExTWnRRES0LPAERES0STATUS

Bits [31:17]

FnV, bit [16]

AET, bits [15:14] When RAS is implemented:

Otherwise:

CM, bit [13]

ExT, bit [12]

WnR, bit [11]

Bit [10]

LPAE, bit [9]

Bits [8:6]

STATUS, bits [5:0]

Accessing the DFSR

MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

When TTBCR.EAE == 0:
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RES0 FnV AET CM ExT WnR FS[4] LPAE RES0 Domain FS[3:0]

AET, bits [15:14]

When RAS is implemented:

When TTBCR.EAE == 1:
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RES0 FnV AET CM ExT WnR RES0 LPAE RES0 STATUS

AET, bits [15:14]

When RAS is implemented: