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Multiply-Accumulate Unit (MAC)
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 4-11
else result[31:0] = 0x7fff_ffff
}
/* scale product before combining with accumulator */
switch (SF) /* 2-bit scale factor */
{
case 0: /* no scaling specified */
break;
case 1: /* SF = “<< 1” */
if (product[31] ^ product[30])
then {MACSR.V = 1
if (inst == MSAC && MACSR.OMC == 1)
then if (product[63] == 1)
then result[31:0] = 0x7fff_ffff
else result[31:0] = 0x8000_0000
else if (MACSR.OMC == 1)
then /* overflowed MAC,
saturationMode enabled */
if (product[63] == 1)
then result[31:0] = 0x8000_0000
else result[31:0] = 0x7fff_ffff
}
else product[31:0] = {product[30:0], 0}
break;
case 2: /* reserved encoding */
break;
case 3: /* SF = “>> 1” */
if (MACSR.OMC == 0 || MACSR.V = 0)
then product[31:0] = {product[31], product[31:1]}
break;
}
/* combine with accumulator */
if (MACSR.V == 0)
then {if (inst == MSAC)
then result[31:0] = acc[31:0] - product[31:0]
else result[31:0] = acc[31:0] + product[31:0]
}
/* check for accumulation overflow */
if (accumulationOverflow == 1)
then {MACSR.V = 1
if (MACSR.OMC == 1)
then /* accumulation overflow,
saturationMode enabled */
if (result[31] == 1)
then result[31:0] = 0x7fff_ffff
else result[31:0] = 0x8000_0000
}
/* transfer the result to the accumulator */
acc[31:0] = result[31:0]
MACSR.N = result[31]
if (result[31:0] == 0x0000_0000)
then MACSR.Z = 1
else MACSR.Z = 0
}