Multiplier Underflow Flag (Mu) - Analog Devices ADSP-2106x SHARC User Manual

2 Computation Units
STKY
Bit Name
6 MOS
7 MVS
8 MUS
9 MIS
Flag update occurs at the end of the cycle in which the status is generated
and is available on the next cycle. If a program writes the ASTAT register
or STKY register explicitly in the same cycle that the multiplier is
performing an operation, the explicit write to ASTAT or STKY supersedes
any flag update from the multiplier operation.

2.6.5.1 Multiplier Underflow Flag (MU)

Underflow is determined for all fixed-point and floating-point multiplier
operations. It is set whenever the result of a multiplier operation is smaller
than the smallest number representable in the output format. It is
otherwise cleared.
For floating-point results, MU and MUS are set whenever the post-
rounded result underflows (unbiased exponent < –126). Denormal
operands are treated as Zeros, therefore they never cause underflows.
For fixed-point results, MU and MUS depend on the data format and are
set under the following conditions:
Twos-complement:
Fractional:
Integer:
Unsigned:
Fractional:
Integer:
If the fixed-point result is sent to an MR register, the underflowed portion
of the result is available in MR0 (fractional result only).
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Definition
Multiplier fixed-point overflow
Multiplier floating-point overflow
Multiplier underflow
Multiplier floating-point invalid operation
upper 48 bits all zeros or all ones, lower 32 bits not all zeros
not possible
upper 48 bits all zeros, lower 32 bits not all zeros
not possible