DSP16411 Datasheet, PDF (19/316 Pages) Agere Systems – DSP16411 Digital Signal Processor

Data Sheet
May 2003
DSP16411 Digital Signal Processor
4 Hardware Architecture (continued)
4.2 DSP16000 Core Architectural Overview
rent state of the cache. The 32-bit csave register holds
the opcode of the instruction following the loop instruc-
tion in program memory.
The DSP16411 contains two identical DSP16000
cores. As shown in Figure 2 on page 21, each core
consists of four major blocks: system control and cache
(SYS), data arithmetic unit (DAU), Y-memory space
address arithmetic unit (YAAU), and X-memory space
address arithmetic unit (XAAU). Bits within the auc0
and auc1 registers configure the DAU mode-controlled
operations. See the DSP16000 Digital Signal Proces-
sor Core Information Manual for a complete description
of the DSP16000 core.
4.2.1 System Control and Cache (SYS)
This section consists of the control block and the
cache.
The control block provides overall system coordination
that is mostly invisible to the user. The control block
includes an instruction decoder and sequencer, a
pseudorandom sequence generator (PSG), an inter-
rupt and trap handler, a wait-state generator, and low-
power standby mode control logic. An interrupt and trap
handler provides a user-locatable vector table and
three levels of user-assigned interrupt priority.
SYS contains the alf register, which is a 16-bit register
that contains AWAIT, a power-saving standby mode
bit, and peripheral flags. The inc0 and inc1 registers
are 20-bit interrupt control registers, and ins is a 20-bit
interrupt status register.
Programs use the instruction cache to store and exe-
cute repetitive operations such as those found in an
FIR or IIR filter section. The cache can contain up to
thirty-one 16-bit and 32-bit instructions. The code in the
cache can repeat up to 2¹⁶ – 1 times without looping
overhead. Operations in the cache that require a coeffi-
cient access execute at twice the normal rate because
the XAAU and its associated bus are not needed for
fetching instructions. The cache greatly reduces the
need for writing in-line repetitive code and, therefore,
reduces instruction/coefficient memory size require-
ments. In addition, the use of cache reduces power
consumption because it eliminates memory accesses
for instruction fetches.
The cache provides a convenient, low-overhead loop-
ing structure that is interruptible, savable, and restor-
able. The cache is addressable in both the X and Y
memory spaces. An interrupt or trap handling routine
can save and restore cloop, cstate, csave, and the
contents of the cache. The cloop register controls the
cache loop count. The cstate register contains the cur-
4.2.2 Data Arithmetic Unit (DAU)
The DAU is a power-efficient, dual-MAC (multiply/accu-
mulate), parallel-pipelined structure that is tailored to
communications applications. It can perform two dou-
ble-word (32-bit) fetches, two multiplications, and two
accumulations in a single instruction cycle. The dual-
MAC parallel pipeline begins with two 32-bit registers,
x and y. The pipeline treats the 32-bit registers as four
16-bit signed registers if used as input to two signed
16-bit x 16-bit multipliers. Each multiplier produces a
full 32-bit result stored into registers p0 and p1. The
DAU can direct the output of each multiplier to a 40-bit
ALU or a 40-bit 3-input ADDER. The ALU and ADDER
results are each stored in one of eight 40-bit accumula-
tors, a0 through a7. Both the ALU and ADDER include
an ACS (add/compare/select) function for Viterbi
decoding. The DAU can direct the output of each accu-
mulator to the ALU/ACS, the ADDER/ACS, or a 40-bit
BMU (bit manipulation unit).
The ALU implements 2-input addition, subtraction, and
various logical operations. The ADDER implements
2-input or 3-input addition and subtraction. To support
Viterbi decoding, the ALU and ADDER have a split
mode in which two simultaneous 16-bit additions or
subtractions are performed. This mode, available in
specialized dual-MAC instructions, is used to compute
the distance between a received symbol and its esti-
mate.
The ACS provides the add/compare/select function
required for Viterbi decoding. This unit provides flags to
the traceback encoder for implementing mode-con-
trolled side-effects for ACS operations. The source
operands for the ACS are any two accumulators, and
results are written back to one of the source accumula-
tors.
The BMU implements barrel-shift, bit-field insertion, bit-
field extraction, exponent extraction, normalization, and
accumulator shuffling operations. ar0 through ar3 are
auxiliary registers whose main function is to control
BMU operations.
The user can enable overflow saturation to affect the
multiplier output and the results of the three arithmetic
units. Overflow saturation can also affect an accumula-
tor value as it is transferred to memory or other
register. These features accommodate various speech
coding standards such as GSM-FR, GSM-HR, and
GSM-EFR. Shifting in the arithmetic pipeline occurs at
several stages to accommodate various standards for
mixed-precision and double-precision multiplications.
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