Using Computational Status - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

Using Computational Status

Though these rounding modes comply with standards set for float-
ing-point data, they also apply for fixed-point multiplier operations on
fractional data. The same two rounding modes are supported, but only the
round-to-nearest operation is actually performed by the multiplier. Using
its local result register for fixed-point operations, the multiplier
rounds-to-zero by reading only the upper bits of the result and discarding
the lower bits.
Using Computational Status
The multiplier and ALU each provide exception information when exe-
cuting floating-point operations. Each unit updates overflow, underflow,
and invalid operation flags in the processing element's arithmetic status
( and
ASTATx ASTATy
An underflow, overflow, or invalid operation from any unit also generates
a maskable interrupt. There are three ways to use floating-point excep-
tions from computations in program sequencing:
• Interrupts. Enable interrupts and use an interrupt service routine
(ISR) to handle the exception condition immediately. This method
is appropriate if it is important to correct all exceptions as they
occur.
• The
ASTATx
test the exception flags in the
instruction executes. This method permits monitoring each
instruction's outcome.
• The
STKYx
to examine exception flags in the
ations. If any flags are set, some of the results are incorrect. This
method is useful when exception handling is not critical.
2-16
) registers and sticky status (
and registers. Use conditional instructions to
ASTATy
and registers. Use the bit test (
STKYy
ADSP-2126x SHARC Processor Hardware Reference
and
STKYx
or registers after the
ASTATx ASTATy
register after a series of oper-
STKY
) registers.
STKYy
) instruction
BTST