PTO-SCALAR-MODEL-BRU-SEMANTICS

1// PTO-UNIT: {"id":"PTO-SCALAR-MODEL-BRU-SEMANTICS","surface":"scalar","classification":["model","bru","semantics"],"depends_on":["PTO-SCALAR-MODEL-ALU-SEMANTICS"]}2// PTO-REQ-SCALAR-CONTROL-001: direct scalar comparison and control transfer.3
4pure func ConditionHolds(condition: ScalarCondition, left: Word, right: Word) => boolean5begin6    case condition of7        when ScalarCondition_EQ  => return left == right;8        when ScalarCondition_NE  => return left != right;9        when ScalarCondition_LT  => return SInt(left) < SInt(right);10        when ScalarCondition_GE  => return SInt(left) >= SInt(right);11        when ScalarCondition_LTU => return UInt(left) < UInt(right);12        when ScalarCondition_GEU => return UInt(left) >= UInt(right);13        when ScalarCondition_Z   => return IsZero(left);14        when ScalarCondition_NZ  => return !IsZero(left);15    end;16end;17
18readonly func ReadBranchPredicate() => Word19begin20    // SETC.* supplies the coupled-bundle predicate. P0..P7 are a distinct21    // register file and have no accepted PTO instruction consumer.22    return _CommitArgument;23end;24
25func BranchRelative(condition: ScalarCondition, left: Word, right: Word,26                    halfword_offset: Word)27begin28    let current_pc = ReadPC();29    if ConditionHolds(condition, left, right) then30        WritePC(current_pc + LSL(halfword_offset, 1));31    else32        WritePC(current_pc + 4);33    end;34end;35
36func JumpRegister(target: Word)37begin38    if target[0] == '1' then39        SetFault(Fault_InstructionPC, target);40    else41        WritePC(target);42    end;43end;44
45func ExecuteCompare(destination: Reg5Selector, condition: ScalarCondition,46                    left: Word, right: Word)47begin48    let result = if ConditionHolds(condition, left, right) then49        Zeros{PTO_XLEN} + 1 else Zeros{PTO_XLEN};50    WriteScalarDestination(destination, result);51end;52
53func ExecuteCompareLogical(destination: Reg5Selector, left: Word,54                           right: Word, combine_or: boolean)55begin56    let logical_result = if combine_or then left OR right else left AND right;57    WriteScalarDestination(destination,58        if IsZero(logical_result) then Zeros{PTO_XLEN}59        else Zeros{PTO_XLEN} + 1);60end;61
62func ExecuteSetCommit(condition: ScalarCondition, left: Word, right: Word)63begin64    _CommitArgument = if ConditionHolds(condition, left, right) then65        Zeros{PTO_XLEN} + 1 else Zeros{PTO_XLEN};66    if _BundleActive then _BARG.taken = !IsZero(_CommitArgument); end;67    _BundleConditionSet = TRUE;68end;69
70func ExecuteSetCommitLogical(left: Word, right: Word, combine_or: boolean)71begin72    let logical_result = if combine_or then left OR right else left AND right;73    _CommitArgument = if IsZero(logical_result) then Zeros{PTO_XLEN}74                      else Zeros{PTO_XLEN} + 1;75    if _BundleActive then _BARG.taken = !IsZero(_CommitArgument); end;76    _BundleConditionSet = TRUE;77end;78
79func SetReturnAddress(halfword_offset: Word)80begin81    let target = ReadTPC() + LSL(halfword_offset, 1);82    // SETRET's assembly destination is Ra (R10). The bundle-local return83    // address mirrors the same target for BSTART.RET and frame recovery.84    WriteGPR(10, target);85    _ReturnAddress = target;86end;87
88func JumpRelative(halfword_offset: Word)89begin90    WritePC(ReadPC() + LSL(halfword_offset, 1));91end;92
93func AddToPC(destination: Reg5Selector, page_offset: Word)94begin95    WriteScalarDestination(destination, ReadTPC() + LSL(page_offset, 12));96end;97