ADSP-21367/ADSP-21368/ADSP-21369
ALU and multiplier operations occur in both processing ele-
ments. These computation units support IEEE 32-bit single-
precision floating-point, 40-bit extended precision floating-
point, and 32-bit fixed-point data formats.
MEMORY ARCHITECTURE
The ADSP-21367/ADSP-21368/ADSP-21369 processors add
the following architectural features to the SIMD SHARC
family core.
Data Register File
On-Chip Memory
A general-purpose data register file is contained in each pro-
cessing element. The register files transfer data between the
computation units and the data buses, and store intermediate
results. These 10-port, 32-register (16 primary, 16 secondary)
register files, combined with the ADSP-2136x enhanced Har-
vard architecture, allow unconstrained data flow between
computation units and internal memory. The registers in PEX
are referred to as R0–R15 and in PEY as S0–S15.
The processors contain two megabits of internal RAM and six
megabits of internal mask-programmable ROM. Each block can
be configured for different combinations of code and data stor-
age (see Table 2 on Page 6). Each memory block supports
single-cycle, independent accesses by the core processor and I/O
processor. The memory architecture, in combination with its
separate on-chip buses, allow two data transfers from the core
and one from the I/O processor, in a single cycle.
Single-Cycle Fetch of Instruction and Four Operands
The SRAM can be configured as a maximum of 64K words of
32-bit data, 128K words of 16-bit data, 42K words of 48-bit
instructions (or 40-bit data), or combinations of different word
sizes up to two megabits. All of the memory can be accessed as
16-bit, 32-bit, 48-bit, or 64-bit words. A 16-bit floating-point
storage format is supported that effectively doubles the amount
of data that may be stored on-chip. Conversion between the
32-bit floating-point and 16-bit floating-point formats is per-
formed in a single instruction. While each memory block can
store combinations of code and data, accesses are most efficient
when one block stores data using the DM bus for transfers, and
the other block stores instructions and data using the PM bus
for transfers.
The ADSP-21367/ADSP-21368/ADSP-21369 feature an
enhanced Harvard architecture in which the data memory
(DM) bus transfers data and the program memory (PM) bus
transfers both instructions and data (see Figure 1 on Page 1).
With separate program and data memory buses and on-chip
instruction cache, the processors can simultaneously fetch four
operands (two over each data bus) and one instruction (from
the cache), all in a single cycle.
Instruction Cache
The processors include an on-chip instruction cache that
enables three-bus operation for fetching an instruction and four
data values. The cache is selective—only the instructions whose
fetches conflict with PM bus data accesses are cached. This
cache allows full-speed execution of core, looped operations
such as digital filter multiply-accumulates, and FFT butterfly
processing.
Using the DM bus and PM buses, with one bus dedicated to
each memory block, assures single-cycle execution with two
data transfers. In this case, the instruction must be available in
the cache.
EXTERNAL MEMORY
Data Address Generators with Zero-Overhead Hardware
Circular Buffer Support
The external port provides a high performance, glueless inter-
face to a wide variety of industry-standard memory devices. The
32-bit wide bus may be used to interface to synchronous and/or
asynchronous memory devices through the use of its separate
internal memory controllers. The first is an SDRAM controller
for connection of industry-standard synchronous DRAM
devices and DIMMs (Dual Inline Memory Module), while the
second is an asynchronous memory controller intended to
interface to a variety of memory devices. Four memory select
pins enable up to four separate devices to coexist, supporting
any desired combination of synchronous and asynchronous
device types. NonSDRAM external memory address space is
shown in Table 3.
The ADSP-21367/ADSP-21368/ADSP-21369 have two data
address generators (DAGs). The DAGs are used for indirect
addressing and implementing circular data buffers in hardware.
Circular buffers allow efficient programming of delay lines and
other data structures required in digital signal processing, and
are commonly used in digital filters and Fourier transforms.
The two DAGs contain sufficient registers to allow the creation
of up to 32 circular buffers (16 primary register sets, 16 second-
ary). The DAGs automatically handle address pointer
wraparound, reduce overhead, increase performance, and sim-
plify implementation. Circular buffers can start and end at any
memory location.
SDRAM Controller
Flexible Instruction Set
The SDRAM controller provides an interface of up to four sepa-
rate banks of industry-standard SDRAM devices or DIMMs, at
speeds up to fSCLK. Fully compliant with the SDRAM standard,
each bank has its own memory select line (MS0–MS3), and can
be configured to contain between 16M bytes and 128M bytes of
memory. SDRAM external memory address space is shown in
Table 4.
The 48-bit instruction word accommodates a variety of parallel
operations, for concise programming. For example, the
ADSP-21367/ADSP-21368/ADSP-21369 can conditionally exe-
cute a multiply, an add, and a subtract in both processing
elements while branching and fetching up to four 32-bit values
from memory—all in a single instruction.
Rev. A
|
Page 5 of 56
|
August 2006
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