NEC Network Controller uPD98502 - Manual (Page 477)

APPENDIX A MIPS III INSTRUCTION SET DETAILS
Preliminary User’s Manual S15543EJ1V0UM 477
DMACC
Doubleword Multiply and Accumulate (1/3)
DMACC
rs
SPECIAL
0 0 0 0 0 0
rt
1
31 26 25 21 20 16 15 0
6 5 5
DMACC
1 0 1 0 0 1
6 5
6
rd sat us 0 0 0
1 5 3
11 10 9 7
Format:
DMACC rd, rs, rt
DMACCU rd, rs, rt
DMACCS rd, rs, rt
DMACCUS rd, rs, rt
Description:
DMACC instruction differs mnemonics by each setting of op codes sat, hi and us as follows.
Mnemonic sat us
DMACC
DMACCU
DMACCS
DMACCUS
0
0
1
1
0
1
0
1
The number of significant bits in the operands of the DMACC instruction differ depending on whether saturation
processing is executed (sat = 1) or not executed (sat = 0).
• When saturation processing is executed (sat = 1): DMACCS, DMACCUS instructions
The contents of general register rs is multiplied by the contents of general register rt. If both operands are set
as "us = 1" (DMACCUS instruction), the contents are handled as 16 bit unsigned data. If they are set as "us =
0" (DMACCS instruction), the contents are handled as 16 bit signed integers. Sign/zero expansion by software
is required for any bits exceeding 16 bits in the operands.
The product of this multiply operation is added to the value in the LO special register. If us = 1, this add
operation handles the values being added as 32 bit unsigned data. If us = 0, the values are handled as 32 bit
signed integers. Sign/zero expansion by software is required for any bits exceeding 32 bits in the LO special
register.
After saturation processing to 32 bits has been performed (see the table below), the sum from this add
operation is loaded to the LO special register. When hi = 1, data that is the same as the data loaded to the HI
special register is also loaded to the rd general register. When hi = 0, data that is the same as the data loaded
to the LO special register is also loaded to the rd general register. Overflow exceptions do not occur.