ꢀ ꢁꢂ ꢃ ꢄ ꢅ ꢆꢇ ꢈ ꢉꢈ ꢀꢊ ꢀ ꢁꢂ ꢃ ꢄ ꢅ ꢆꢇ ꢈ ꢉꢋ ꢀꢊ ꢀ ꢁꢂ ꢃ ꢄꢅ ꢆꢇ ꢈꢉ ꢇꢀ
ꢌ ꢍꢎ ꢏꢐꢑꢒꢓ ꢍ ꢔꢀ ꢐꢍ ꢕꢍ ꢀꢖꢗ ꢂꢍ ꢕ ꢔꢖꢗ ꢒꢘ ꢓ ꢆꢏ ꢂ ꢂꢓ ꢘ ꢂ
SPRS226H − NOVEMBER 2003 − REVISED AUGUST 2005
CPU (DSP core) description
The CPU fetches VelociTI advanced very-long instruction words (VLIWs) (256 bits wide) to supply up to eight
32-bit instructions to the eight functional units during every clock cycle. The VelociTI VLIW architecture
features controls by which all eight units do not have to be supplied with instructions if they are not ready to
execute. The first bit of every 32-bit instruction determines if the next instruction belongs to the same execute
packet as the previous instruction, or whether it should be executed in the following clock as a part of the next
execute packet. Fetch packets are always 256 bits wide; however, the execute packets can vary in size. The
variable-length execute packets are a key memory-saving feature, distinguishing the C64x CPUs from other
VLIW architectures. The C64x VelociTI.2 extensions add enhancements to the TMS320C62x DSP
VelociTI architecture. These enhancements include:
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Register file enhancements
Data path extensions
Quad 8-bit and dual 16-bit extensions with data flow enhancements
Additional functional unit hardware
Increased orthogonality of the instruction set
Additional instructions that reduce code size and increase register flexibility
The CPU features two sets of functional units. Each set contains four units and a register file. One set contains
functional units .L1, .S1, .M1, and .D1; the other set contains units .D2, .M2, .S2, and .L2. The two register files
each contain 32 32-bit registers for a total of 64 general-purpose registers. In addition to supporting the packed
16-bit and 32-/40-bit fixed-point data types found in the C62x VelociTI VLIW architecture, the C64x register
files also support packed 8-bit data and 64-bit fixed-point data types. The two sets of functional units, along with
two register files, compose sides A and B of the CPU [see the functional block and CPU (DSP core) diagram,
and Figure 1]. The four functional units on each side of the CPU can freely share the 32 registers belonging to
that side. Additionally, each side features a “data cross path”—a single data bus connected to all the registers
on the other side, by which the two sets of functional units can access data from the register files on the opposite
side. The C64x CPU pipelines data-cross-path accesses over multiple clock cycles. This allows the same
register to be used as a data-cross-path operand by multiple functional units in the same execute packet. All
functional units in the C64x CPU can access operands via the data cross path. Register access by functional
units on the same side of the CPU as the register file can service all the units in a single clock cycle. On the C64x
CPU, a delay clock is introduced whenever an instruction attempts to read a register via a data cross path if that
register was updated in the previous clock cycle.
In addition to the C62x DSP fixed-point instructions, the C64x DSP includes a comprehensive collection of
quad 8-bit and dual 16-bit instruction set extensions. These VelociTI.2 extensions allow the C64x CPU to
operate directly on packed data to streamline data flow and increase instruction set efficiency.
Another key feature of the C64x CPU is the load/store architecture, where all instructions operate on registers
(as opposed to data in memory). Two sets of data-addressing units (.D1 and .D2) are responsible for all data
transfers between the register files and the memory. The data address driven by the .D units allows data
addresses generated from one register file to be used to load or store data to or from the other register file. The
C64x .D units can load and store bytes (8 bits), half-words (16 bits), and words (32 bits) with a single instruction.
And with the new data path extensions, the C64x .D unit can load and store doublewords (64 bits) with a single
instruction. Furthermore, the non-aligned load and store instructions allow the .D units to access words and
doublewords on any byte boundary. The C64x CPU supports a variety of indirect addressing modes using either
linear- or circular-addressing with 5- or 15-bit offsets. All instructions are conditional, and most can access any
one of the 64 registers. Some registers, however, are singled out to support specific addressing modes or to
hold the condition for conditional instructions (if the condition is not automatically “true”).
TMS320C62x is a trademark of Texas Instruments.
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