LD64B -- A64

LD64B

Single-copy atomic 64-byte Load

This instruction derives an address from a base register value, loads eight 64-bit doublewords from a memory location, and writes them to consecutive registers. The load starts at register Xt, with the data being read as X(t+7)::X(t+6)::X(t+5)::X(t+4)::X(t+3)::X(t+2)::X(t+1)::Xt = Data[511:0]. The data is loaded atomically and is required to be 64-byte aligned.

It is IMPLEMENTATION DEFINED which memory locations support this instruction. A memory location that supports LD64B also supports ST64B.

For more information, including about the memory types accessible and how the accesses are performed, see Single-copy atomic 64-byte load/store.

Integer
(FEAT_LS64)

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
1	1	1	1	1	0	0	0	0	0	1	1	1	1	1	1	1	1	0	1	0	0	Rn					Rt
size					VR			A	R		Rs					o3	opc

Encoding

LD64B <Xt>, [<Xn|SP> {, #0}]

Decode for this encoding

if !IsFeatureImplemented(FEAT_LS64) then EndOfDecode(Decode_UNDEF); end; if Rt[4:3] == '11' || Rt[0] == '1' then EndOfDecode(Decode_UNDEF); end; let withstatus : boolean = FALSE; let t : integer{} = UInt(Rt); let n : integer{} = UInt(Rn); let tagchecked : boolean = n != 31;

For information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly LD64B.

Assembler Symbols

<Xt>	Is the 64-bit name of the first general-purpose register to be transferred, encoded in the "Rt" field.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

Operation

CheckLDST64BEnabled(); var data : bits(512); var address : bits(64); var value : bits(64); let accdesc : AccessDescriptor = CreateAccDescLS64(MemOp_LOAD, withstatus, tagchecked); if n == 31 then CheckSPAlignment(); address = SP{64}(); else address = X{64}(n); end; data = MemLoad64B(address, accdesc); for i = 0 to 7 do value = data[63+64*i : 64*i]; if BigEndian(accdesc.acctype) then value = BigEndianReverse{64}(value); end; X{64}(t+i) = value; end;