ADSP-BF535 Blackfin Processor Hardware Reference
2-21
Computational Units
Biased rounding affects the result only when the
A0.L/A1.L
register con-
tains 0x8000; all other rounding operations work normally. This mode
allows more efficient implementation of bit specified algorithms that use
biased rounding, for example, the Global System for Mobile Communica-
tions (GSM) speech compression routines.
Truncation
Another common way to reduce the significant bits representing a number
is to simply mask off the N-M lower bits. This process is known as
trunca-
tion
and results in a relatively large bias. Instructions that do not support
rounding revert to truncation. The
RND_MOD
bit in
ASTAT
has no effect on
truncation.
Special Rounding Instructions
The ALU provides the ability to round the arithmetic results directly into
a data register with biased or unbiased rounding as described above. It also
provides the ability to round on different bit boundaries. The options
Figure 2-8. Biased Rounding in Multiplier Operation
0 x 0 0
0 0 0 0
8 0 0 0 0 x 0 0
0 0 0 1
8 0 0 0 0 x 0 0
0 0 0 0
0 0 0 0
0 x 0 0
0 0 0 1
8 0 0 0 0 x 0 0
0 0 0 2
0 0 0 0 0 x 0 0
0 0 0 2
0 0 0 0
0 x 0 0
0 0 0 0
8 0 0 1 0 x 0 0
0 0 0 1
0 0 0 1 0 x 0 0
0 0 0 1
0 0 0 1
0 x 0 0
0 0 0 1
8 0 0 1 0 x 0 0
0 0 0 2
0 0 0 1 0 x 0 0
0 0 0 2
0 0 0 1
0 x 0 0
0 0 0 0
7 F F F 0 x 0 0
0 0 0 0
F F F F 0 x 0 0
0 0 0 0
F F F F
0 x 0 0
0 0 0 1
7 F F F 0 x 0 0
0 0 0 1
F F F F 0 x 0 0
0 0 0 1
F F F F
A0/A1 before RND
Biased RND result
Unbiased RND result
Summary of Contents for ADSP-BF535 Blackfin
Page 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Page 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Page 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Page 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Page 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Page 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Page 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Page 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Page 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...