Mpyr, Signed fractional multiply, Operation assembler syntax – Freescale Semiconductor StarCore SC140 User Manual
Page 636
A-322
SC140 DSP Core Reference Manual
MPYR
MPYR
Signed Fractional Multiply
MPYR
and Round (DALU)
Description
Status and Conditions that Affect Instruction
Status and Conditions Changed by Instruction
Example
mpyr d4,d5,d6
Operation
Assembler Syntax
Rnd((Da.H * Db.H))
→ Dn
MPYR Da,Db,Dn
MPYR Da,Db,Dn
Performs signed fractional multiplication of the high portions of a data register pair (Da, Db), rounds the
product, and stores the result in a destination data register (Dn). Rounding adjusts the LSB of the high part
of the destination register according to the value of the low part of the register and then zeros the low part.
The two modes of the round function, Rnd(), are described on page A-359.
Register Address
Bit Name
Description
SR[2]
SM
If set, selects 32-bit arithmetic saturation mode.
SR[3]
RM
Rounding mode
SR[5:4]
S[1:0]
Scaling bits determine which bits in the result are used in the Ln bit
calculation and which bits are used in rounding.
Register Address
Bit Name
Description
Ln
L
If not in arithmetic saturation mode (SR [SM] = 0), calculates and
updates the Ln bit in the destination register. If in arithmetic
saturation mode (SR [SM] = 1), clears the Ln bit in the destination
register.
EMR[2]
DOVF
Set if the result cannot be represented in 40 bits, or if the result
saturates to 32 bits in saturation mode.
Register/Memory Address
Before
After
SR
$00E0 0000
D4
$00 4001 0000
D5
$00 4002 0000