Encoding:

Format:

MFHC0 rt, rd, sel

Purpose:

Move from High Coprocessor 0

To move the contents of the upper 32 bits of a Coprocessor 0 register, extended by 32-bits, to a general register.

Description:

 GPR[rt] = CPR[0,rd,sel][63:32]

The contents of the Coprocessor 0 register specified by the combination of rd and sel are sign-extended and loaded into general register rt. Not all Coprocessor 0 registers support the sel field, and in those instances, the sel field must be zero.

When the Coprocessor 0 register specified is the EntryLo0 or the EntryLo1 register, MFHC0 must undo the effects of

MTHC0, that is, bits 31:30 of the register must be returned as bits 1:0 of the GPR, and bits 32 and those of greater significance must be left-shifted by two and written to bits 31:2 of the GPR. This is because the RI and XI bits are repositioned on the write from GPR to EntryLo0 or the EntryLo1.

Restrictions:

Pre-Release 6: The results are UNDEFINED if Coprocessor 0 does not contain a register as specified by rd and sel, or the register exists but is not extended by 32-bits, or the register is extended for XPA, but XPA is not supported or enabled.

Release 6: Reading the high part of a register that is reserved, not implemented for the current core configuration, or that is not extended beyond 32 bits returns 0.

Availability and Compatibility:

This feature supports MIPS32 backward-compatibility on MIPS64 implementations.

Operation:

PABITS is the total number of physical address bits implemented. PABITS is defined in the descriptions of EntryLo0 and EntryLo1.

if Config5MVH = 0 then SignalException(ReservedInstruction) endif
reg = rd
if IsCoprocessorRegisterImplemented(0, reg, sel) and 
   IsCoprocessorRegisterExtended(0, reg, sel) then
   data = CPR[0, reg, sel]
   if (reg,sel = EntryLo1 or reg,sel = EntryLo0) then
       if (Config3LPA = 1 and PageGrainELPA = 1) then // PABITS > 36
           GPR[rt]31..0 = data61..30
           GPR[rt]63..32 = (data61)32 // sign-extend
      else
         GPR[rt] = 0
       endif
   else
       GPR[rt] = sign_extend(data63..32)
   endif
else
   if ArchitectureRevision() >= 6 then
       GPR[rt] = 0
   else
      UNDEFINED
   endif
endif

Exceptions:

Coprocessor Unusable, Reserved Instruction