CASW

assembly

[
  "casw [SrcL], SrcR, SrcD, ->Rd",
  "casw.aq [SrcL], SrcR, SrcD, ->Rd",
  "casw.rl [SrcL], SrcR, SrcD, ->Rd",
  "casw.aqrl [SrcL], SrcR, SrcD, ->Rd"
]

block

[]

catalog_indices

[
  53
]

catalog_records

[
  {
    "asm": "casw<.{aq, rl, aqrl}> [SrcL], SrcR, SrcD, ->{t, u, Rd}",
    "constraints": [],
    "encoding": [
      {
        "index": 0,
        "mask": "0x0000707f",
        "match": "0x0000201b",
        "width_bits": 32
      }
    ],
    "encoding_kind": "L32",
    "fields": [
      {
        "name": "RegDst",
        "pieces": [
          {
            "instruction_lsb": 7,
            "value_lsb": 0,
            "width": 5
          }
        ],
        "signedness": "encoding-defined",
        "width": 5
      },
      {
        "name": "SrcD",
        "pieces": [
          {
            "instruction_lsb": 27,
            "value_lsb": 0,
            "width": 5
          }
        ],
        "signedness": "encoding-defined",
        "width": 5
      },
      {
        "name": "SrcL",
        "pieces": [
          {
            "instruction_lsb": 15,
            "value_lsb": 0,
            "width": 5
          }
        ],
        "signedness": "encoding-defined",
        "width": 5
      },
      {
        "name": "SrcR",
        "pieces": [
          {
            "instruction_lsb": 20,
            "value_lsb": 0,
            "width": 5
          }
        ],
        "signedness": "encoding-defined",
        "width": 5
      },
      {
        "name": "aq",
        "pieces": [
          {
            "instruction_lsb": 26,
            "value_lsb": 0,
            "width": 1
          }
        ],
        "signedness": "encoding-defined",
        "width": 1
      },
      {
        "name": "rl",
        "pieces": [
          {
            "instruction_lsb": 25,
            "value_lsb": 0,
            "width": 1
          }
        ],
        "signedness": "encoding-defined",
        "width": 1
      }
    ],
    "form_id": "casw_32_cb29e4287223",
    "length_bits": 32,
    "mnemonic": "CASW",
    "semantic_family": "AMO",
    "semantic_group": "AMO",
    "semantic_handler": "CompareAndSwap",
    "semantic_summary": "CASW atomically compares and conditionally replaces one word, then publishes the prior value.",
    "status": "accepted"
  }
]

classification

[
  "amo"
]

contract

{
  "block_composition": [
    "none"
  ],
  "canonical_assembly": [
    "casw [SrcL], SrcR, SrcD, ->Rd",
    "casw.aq [SrcL], SrcR, SrcD, ->Rd",
    "casw.rl [SrcL], SrcR, SrcD, ->Rd",
    "casw.aqrl [SrcL], SrcR, SrcD, ->Rd"
  ],
  "defaults": [
    "SrcL, SrcR, SrcD, and RegDst are required Reg5 fields. Encoded source zero reads the architectural zero register; encoded destination zero discards the old value.",
    "aq=0 and rl=0 select relaxed ordering. aq=1 selects acquire, rl=1 selects release, and aq=1 with rl=1 selects acquire-release.",
    "The short form has no far field and therefore uses the default flat-address route."
  ],
  "encoding_class": "standalone-encoded",
  "examples": [
    "casw [a0], a1, a2, ->a3",
    "casw.aqrl [t#1], u#1, a0, ->u"
  ],
  "exceptions": [
    "The effective address must be aligned to 4 bytes. Alignment, read translation/permission, write translation/permission, and translated-address equality are checked before effects.",
    "On a fault, no destination, memory write, event, reservation update, or TPC advance occurs. Trap entry saves the original TPC and recovery restores it for full reissue.",
    "An undecodable fixed-bit pattern raises Fault_IllegalInstruction before effects. All explicit field values are assigned."
  ],
  "field_contracts": {},
  "field_zero_meanings": {
    "RegDst": "Encoded zero discards the prior value.",
    "SrcL": "Encoded zero reads the architectural zero register as the address.",
    "SrcR": "Encoded zero supplies numeric zero as the expected value.",
    "SrcD": "Encoded zero supplies numeric zero as the desired value.",
    "aq": "Encoded zero disables acquire ordering.",
    "rl": "Encoded zero disables release ordering."
  },
  "legality": [
    "All 32 SrcL, SrcR, and SrcD Reg5 encodings are assigned: 0..23 select absolute GPRs, 24..27 select T#1..T#4, and 28..31 select U#1..U#4.",
    "All 32 RegDst encodings are assigned. Code 0 and codes 24..29 discard, code 30 pushes U, code 31 pushes T, and codes 1..23 write the named absolute GPR.",
    "All aq and rl combinations are assigned; the short form has implicit far zero.",
    "The effective address must be aligned to 4 bytes."
  ],
  "memory_effects": [
    "After aligned read and write preflight identify the same translated location, atomically read one 4-byte word and compare it with SrcR truncated to 4 bytes.",
    "On equality, store SrcD truncated to 4 bytes and set write_performed in the atomic event. On mismatch, preserve memory and emit an ordered atomic event with write_performed false.",
    "Only a successful overlapping write invalidates the local 64-byte-line reservation; mismatch and nonoverlap preserve it.",
    "The 32-bit old value is sign-extended to XLEN."
  ],
  "operands": [
    {
      "field": "SrcL",
      "role": "Reg5 atomic address source"
    },
    {
      "field": "SrcR",
      "role": "Reg5 expected word source"
    },
    {
      "field": "SrcD",
      "role": "Reg5 desired word source"
    },
    {
      "field": "RegDst",
      "role": "Reg5 old-value destination"
    },
    {
      "field": "aq",
      "role": "acquire ordering bit"
    },
    {
      "field": "rl",
      "role": "release ordering bit"
    }
  ],
  "ordering": [
    "aq=0,rl=0 records relaxed ordering; aq=1,rl=0 acquire; aq=0,rl=1 release; aq=1,rl=1 acquire-release for both match and mismatch.",
    "The short form always uses the default flat-address route."
  ],
  "standalone_opcode": true,
  "state_effects": [
    "Snapshot SrcL, SrcR, and SrcD before any memory or destination effect.",
    "Publish the prior value after every nonfaulting match or mismatch; publish no value on fault.",
    "The 32-bit old value is sign-extended to XLEN.",
    "Successful execution advances TPC by 4 bytes. A fault saves and later restores the original TPC for full reissue."
  ]
}

depends_on

[
  "PTO-BLOCK-MODEL-SCHEMA-PROFILE-ENCODING"
]

id

PTO-SCALAR-CASW

mnemonic

CASW

summary

CASW atomically compares and conditionally replaces one word, then publishes the prior value.

surface

scalar

{
  "classification": [
    "amo"
  ],
  "documentation": "docs/scalar/amo/CASW.md",
  "id": "PTO-SCALAR-CASW",
  "instruction_contract": {
    "artifact": "spec/evidence/instruction-contract-closure.json",
    "mnemonic": "CASW",
    "ndf_clause": "PTO-INST-SCALAR-CASW"
  },
  "mnemonic": "CASW",
  "readiness_subjects": [
    "ADR-0020",
    "ADR-0030",
    "ADR-0059"
  ],
  "semantic_tests": [
    "PTO-AVS-SCALAR-CASW-MATCH-001",
    "PTO-AVS-SCALAR-CASW-MISMATCH-001",
    "PTO-AVS-SCALAR-CASW-PRECISE-001"
  ],
  "source": "asl/scalar/amo/CASW.asl",
  "surface": "scalar",
  "tests": [
    "PTO-AVS-SCALAR-CASW-DECODE-001",
    "PTO-AVS-SCALAR-CASW-MATCH-001",
    "PTO-AVS-SCALAR-CASW-MISMATCH-001",
    "PTO-AVS-SCALAR-CASW-PRECISE-001"
  ]
}