A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
which targets low-level hardware, most commonly used in the programming of FPGAs. It is a rich subset of C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, with non-standard extensions to control hardware instantiation with an emphasis on parallelism. Handel-C is to hardware design what the first high level programming languages were to programming CPUs. Unlike many other design languages that target a specific architecture Handel-C can be compiled to a number of design languages and then synthesised to the corresponding hardware. This frees developers to concentrate on the programming task at hand rather than the idiosyncrasies of a specific design language and architecture.
Additional features
The subset of C includes all common C language features necessary to describe complex algorithms. Like many embedded C compilers, floating point data types were omitted. Floating point arithmetic is supported through external libraries that are very efficient.
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...
In computer science, Communicating Sequential Processes is a formal language for describing patterns of interaction in concurrent systems. It is a member of the family of mathematical theories of concurrency known as process algebras, or process calculi...
keywords are used, along with the general file structure of Occam.
For example:
par {
++c;
a = d + e;
b = d + e;
}
Channels
Channels provide communication between parallel threads, one of the paths outputs data onto the channel and the other parallel thread can read the data. Channels can be created with or without a FIFO
FIFO
FIFO is an acronym for First In, First Out, an abstraction related to ways of organizing and manipulation of data relative to time and prioritization...
FIFO is an acronym for First In, First Out, an abstraction related to ways of organizing and manipulation of data relative to time and prioritization...
the first thread to execute the channel read (or write) command waits until the corresponding write (or read) is executed in the other communicating thread. In this way the sender and receiver rendezvous and can pass a datum from one to the other and so synchronize their operation in a cooperative manner.
Scope and variable sharing
The scope of declarations are limited to the code blocks ({ ... }) in which they were declared, the scope is hierarchical in nature as declarations are in scope within sub blocks.
For example:
int a;
void main(void)
{
int b;
/* "a" and "b" are within scope */
{
int c;
/* "a", "b" and "c" are within scope */
}
{
int d;
/* "a", "b" and "d" are within scope */
}
}
Extensions to the C language
In addition to the effects the standard semantics of C have on the timing of the program, the following keywords are reserved for describing the practicalities of the FPGA environment or for the language elements sourced from Occam:
Types and Objects
Expressions
Statements
chan
< ... > (type clarifier)
! (send into channel)
chanin
[ : ] (bit range selection)
? (read from channel)
chanout
\\ (drop)
delay
macro expr
<- (take)
ifselect
external
@ (concatenation operator)
set intwidth
external_divide
select
let ... ; in
inline
width
par
interface
prialt
internal
releasesema
internal_divide
set clock
mpram
set family
macro proc
set part
ram
set reset
rom
seq
sema
try { ... } reset
shared
trysema
signal
with
typeof
undefined
wom
Scheduling
In Handel-C, assignment and the delay command take one cycle. All other operations are "free" . This allows programmers to manually schedule tasks and create effective pipelines
Instruction pipeline
An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput ....
. By arranging loops in parallel with the correct delays, a pipeline can massively speed up a program.
The Department of Computer Science, until 2011 named the Computing Laboratory , is a department of Oxford University in England...
hardware description languages developed by the hardware compilation group. Handel HDL evolved into Handel-C around early 1996. The technology developed at Oxford was spun off to mature as a cornerstone product for Embedded Solutions Limited (ESL) in 1996. ESL was renamed Celoxica in September 2000.
Handel-C was adopted by many University Hardware Research groups after its release by ESL, as a result was able to established itself as a hardware design tool of choice within the academic community, especially in the United Kingdom.
In early 2008, Celoxica's ESL business was acquired by Catalytic, a startup selling a MATLAB to C tool. Soon thereafter, Celoxica and Catalytic merged to form Agility, which developed and sold, among other products, ESL tools supporting Handel-C.
In early 2009, Agility ceased operations after failing to obtain further capital investments or credit
In January 2009, Mentor Graphics acquired Agility's C synthesis assets.
Other subset C HDL's that developed around the same time are Transmogrifier C in 1994 at University of Toronto
University of Toronto
The University of Toronto is a public research university in Toronto, Ontario, Canada, situated on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution of higher learning in Upper Canada...
FpgaC is a compiler for a subset of the C programming language, which produces digital circuits that will execute the compiled programs. The circuits may use FPGAs or CPLDs as the target processor for reconfigurable computing, or even ASICs for dedicated applications...
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
(now licensed to Impulse Accelerated Technologies under the name Impulse C
Impulse C
Impulse C is a subset of the C programming language combined with a C-compatible function library supporting parallel programming, in particular for programming of applications targeting FPGA devices...
