View source for Engineering:Super Harvard Architecture Single-Chip Computer

The '''Super Harvard Architecture Single-Chip Computer''' ('''SHARC''') is a high performance floating-point and [[Fixed-point arithmetic|fixed-point]] [[Engineering:Digital signal processor|DSP]] from Analog Devices. SHARC is used in a variety of signal processing applications ranging from [[Audio signal processing|audio processing]], to single-CPU guided artillery shells to 1000-CPU over-the-horizon radar processing computers. The original design dates to about January 1994.

SHARC processors are typically intended to have a good number of serial links to other SHARC processors nearby, to be used as a low-cost alternative to [[Symmetric multiprocessing|SMP]].

==Architecture==
The SHARC is a [[Harvard architecture]] [[Word addressing|word-addressed]] VLIW processor; it knows nothing of 8-bit or 16-bit values since each address is used to point to a whole 32-bit word, not just an [[Octet (computing)|octet]]. It is thus neither little-endian nor big-endian, though a compiler may use either convention if it implements 64-bit data and/or some way to pack multiple 8-bit or 16-bit values into a single 32-bit word. In C, the characters are 32-bit as they are the smallest addressable words by standard.

The word size is [[48-bit|48-bit]] for instructions, [[32-bit|32-bit]] for integers and normal floating-point, and 40-bit for extended floating-point. Code and data are normally fetched from on-chip memory, which the user must split into regions of different word sizes as desired. Small data types may be stored in wider memory, simply wasting the extra space. A system that does not use 40-bit extended floating-point might divide the on-chip memory into two sections, a 48-bit one for code and a 32-bit one for everything else. Most memory-related CPU instructions can not access all the bits of 48-bit memory, but a special 48-bit register is provided for this purpose. The special 48-bit register may be accessed as a pair of smaller registers, allowing movement to and from the normal registers.

Off-chip memory can be used with the SHARC. This memory can only be configured for one single size. If the off-chip memory is configured as 32-bit words to avoid waste, then only the on-chip memory may be used for code execution and extended floating-point. Operating systems may use [[Overlay (programming)|overlays]] to work around this problem, transferring 48-bit data to on-chip memory as needed for execution. A [[Direct memory access|DMA]] engine is provided for this. True paging is impossible without an external [[Memory management unit|MMU]].

The SHARC has a 32-bit word-addressed address space. Depending on word size this is 16 GB, 20 GB, or 24 GB (using the common definition of an 8-bit "byte").

SHARC instructions may contain a 32-bit immediate operand. Instructions without this operand are generally able to perform two or more operations simultaneously. Many instructions are conditional, and may be preceded with "if ''condition'' " in the [[Assembly language|assembly language]]. There are a number of ''condition'' choices, similar to the choices provided by the [[X86|x86]] flags register.

There are two [[Delay slot|delay slot]]s. After a jump, two instructions following the jump will normally be executed.

The SHARC processor has built-in support for loop control. Up to 6 levels may be used, avoiding the need for normal branching instructions and the normal bookkeeping related to loop exit.

The SHARC has two full sets of general-purpose registers. Code can instantly switch between them, allowing for fast context switches between an application and an [[Operating system|OS]] or between two threads.

==See also==
*[[Engineering:TigerSHARC|TigerSHARC]]
*[[Engineering:Blackfin|Blackfin]]
*[[Qualcomm Hexagon]]
*[[Engineering:Texas Instruments TMS320|Texas Instruments TMS320]]
*[[Company:CEVA, Inc.|CEVA, Inc.]]

==External links==
*[http://www.analog.com/en/processors-dsp/sharc/products/index.html SHARC processors website]

[[Category:Digital signal processors]]

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