Encoding:

Format:

MTLO rs, ac

Purpose:

Move to LO register

To copy a GPR to the special purpose LO part of the specified accumulator register.

Description:

LO[ac] = GPR[rs]

Thesource register rs is copied to the LO part of accumulator ac. The LO part of the accumulator is defined to be bits

0 to 32 of the DSP Module accumulator register.

The value of ac can range from 0 to 3. When ac=0, this refers to the original HI/LO register pair of the MIPS32 architecture.

In Release 6 of the MIPS Architecture, accumulators are eliminated from MIPS32.

Restrictions:

A computed result written to the HI/LO pair by DIV, DIVU, DDIV, DDIVU, DMULT, DMULTU, MULT, or MULTU must be read by MF HI or MFLO before a new result can be written into either HI or LO. Note that this restriction only applies to the original HI/LO accumulator pair, and does not apply to the new accumulators, ac1, ac2, and ac3.

If an MTHI instruction is executed following one of these arithmetic instructions, but before an M FLO or MFHI instruction, the contents of LO are UNPREDICTABLE. The following example shows this illegal situation:

MULT r2,r4 # start operation that will eventually write to HI,LO
...        # code not containing mfhi or mflo
MTHI r6
...        # code not containing mflo
MFLO r3    # this mflo would get an UNPREDICTABLE value

Operation:

if (( ac != 0 ) or (ConfigAR >= )) then 
   ValidateAccessToDSPResources()
endif
LO[ac]31..0 = GPR[rs]31..0

Exceptions:

Reserved Instruction, DSP Disabled