Chapter 16
Appendix
XVI - 72 Extension Instruction Specification
2) Precautions for describing word/halfword data multiply and accumulate instruction and multiply and accu-
mulate instruction
When a word/halfword data multiply and accumulate instruction and multiply and accumulate instruction
are executed continuously with the former instruction preceding the latter, the result of the word/halfword
data multiply and accumulate instruction is used to execute the sequential multiply and accumulate
instruction. For this reason, the next multiply and accumulate instruction must be activated after the
result of the word/halfword data multiply and accumulate instruction, that is required for the multiply and
accumulate instruction, has been output. Therefore, it is necessary to provide 2 cycles between the
preceding word/halfword data multiply and accumulate instruction and the succeeding multiply and
accumulate instruction.
Figure:16.4.4 Drawing of Pipelining for Precaution (2)
This precaution is applicable to the following instructions:
<Word/halfword data multiply and accumulate instructions>
MAC, MACI, MACH, MACIH, MACU, MACIU, MACHU and MACIHU instructions
<Multiply and accumulate instructions>
MAC, MACI, MACH, MACIH, MACU, MACIU, MACHU, MACIHU, MACB, MACIB,
MACBU and MACIBU instructions
DEC
Word/halfword data
multiply and accumulate
instruction (1)
Insert 2 cycles
Result available
for reference
Multiply and accumulate
instruction (2)
Instruction
decoding
Instruction
decoding
Operation
Operation
Multiply and accumulate
instruction (1) outputs
the result required for
multiply and accumulate
instruction (2)
EX
MEM
WB
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