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 HDLPlanet Knowledge Capsule        Oct 2003
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"All truth passes through three stages. First, it is ridiculed. Second, it is
violently opposed. Third, it is accepted as being self-evident." 
                                              - Arthur Schopenhauer (1788-1860)
 
Editor's note :

  Good Morning...
  I was thinking whether the name "news letter" is really suitable for the kind
  of information captured in this e-zine. It is very less news and more of
  knowledge. So I decided to name it as "Knowledge Capsule" which is also the
  name of the main section involved in this e-zine. So... your knowledge is sure
  to grow with every "Knowledge Capsule".


I. Tools in News 
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 - Mentor Graphics claims that it has improved simulation performance by 2x in
   its latest modelsim release (Modelsim 5.7) 
   http://www.model.com/news_events/pr/modelSim57.pdf

 - HDL & Matlab co-simulation : Aldec's Active-HDL version 6.1 allows system
   designers to cosimulate models in Simulink and digital logic developed in 
   Active-HDL.
   http://www.eedesign.com/story/OEG20031022S0026

II. Knowledge capsule
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o For the blooming professionals

  - Article : Physics is not the hurdle for scaling CMOS
              http://www.eet.com/futureofsemis/limits/OEG20030923S0037

o For the budding professionals
  - What is Superscalar Architecture ?

   In a simplest computer architecture, only a single instruction can be
   executed in a clock cycle. In a "superscalar" architecture, extra compute
   resources are added to achieve another dimension of instruction-level
   parallelism. Superscalar architecture refers to the use of multiple execution
   units, to allow the processing of more than one instruction at a time. This
   can also be thought of as a form of "internal multiprocessing". 

   Most of the operations involving PC (Program Counter) is with the integer
   information. The same integer handling unit can't be used for floating-point
   operations. They are handled differently using a dedicated unit called the
   floating point unit (FPU). (Yes, on some computers, the integer units do have
   the capability to handle floating point data, but relatively slower than the
   dedicated units.

   Older processors have only one of these units, and instructions are processed
   sequentially. Present day processors use multiple execution units allowing
   more than one instruction to be executed simultaneously, increasing
   performance. Processors with this capability are said to be Superscalar. The
   original Pentium provided 2 separate pipelines that Intel called the U and V
   pipelines. In theory, each pipeline could be working simultaneously on 2
   differerent sets of instructions.

   Being superscalar is not so easy, it comes with much more headache. Since
   multiple instructions can be despatched to multiple execution units
   (pipelines) simultaneously, the data on one pipeline could depend on the
   other and could have data hazards. Though data hazards are possible on
   processors with sigle pipeline also, the complexity involved in resolving it
   in superscalar processors is much more. Control hazards can get worse since
   instruction fetch bandwidth increases (doubled for dual pipelined machine).
   Mispredicted branches may require both pipelines to be flushed. All these and
   many more such cases need to be taken care of in the Superscalar
   Architecture.

  - What is DMA (Direct Memory Access) ?

   It is a means by which a peripheral can control the processors memory bus
   independently without actual intervention from the processor. There is a
   good article published about "Introduction to Direct Memory Access" worth
   reading. Follow the below Link:
   http://www.embedded.com/shared/printableArticle.jhtml?articleID=15300200


III. Automation Arena
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Learning Tcl made easy - Part 2

Control Flow
    As in any other programming language (like C), Tcl also has "if", "while"
    and "for" as the basic control flow constructs. One other construct in Tcl
    is "foreach", this doesn't have a C equivalent. Another useful construct is
    the "switch" construct. This is very similar to the case construct in C.

	If Construct :
		if { condition1 } {
		--------
		} elsif { condition2 } {
		--------
		} else {
		--------
		}
	
	While Construct :
		while { condition } {
		--------
		}

	Foreach Construct : (Example)
		set cities { Bangalore Houston Amsterdam }
		foreach city $cities {
			puts "$city";
		}

		This is result in printing the following on STDOUT:
			Bangalore
			Houston
			Amsterdam

	Switch Construct : (Example)
		switch $alpha {
			a { puts "found a"}
			b { puts "found b"}
			c { puts "found c"}
		}

Arrays
    Arrays are always unidimensional but the index is a string. If you use a
    separator in the index string (such as ',', '-'), you can get the same
    effect than with a multidimensional array in other languages.

	Example :
		set temperatures { Bangalore 10 20	Delhi 5 35 Rajkot 15 35 }
		foreach {town Tmin Tmax} $observations {
   			set Temp($town-min) $Tmin
   			set Temp($town-max) $Tmax
   		}

        Temp is an array here, $town-min and $town-max are the array indices
        Tmin and Tmax are the values. So this way the unidimensional array
        temperatures can be viewed as multidimensional by having it defined like
        the array Temp.

Procedures
	Procedures are equivalent to C functions.

	Example : 
		proc sum2 {a b} {
			expr $a + $b
		}

        If the procedure doesn't contain a return statement, the value computed
        in the last statement is itself the return value. Hence the above
        procedure is same as the one below.

		proc sum2 {a b} {
			return [expr $a + $b]
		}
	

Eval Command
	- Concatenate all its arguments in one string 
	- splits this string using spaces as separators 
	- evaluate the command sentence formed by all the substrings 

	Example : 
		proc sum {args} {
			set result 0
			foreach n $args {
				set result [expr $result+$n]
			}
			return $result
		}

		proc average {args} {
			return [expr [eval sum $args] / [llength $args]] 
		} 

        If you had omitted the 'eval' command in the previous example, the 'sum'
        procedure would have returned an error because 'sum' should be called
        with only one string argument (in the previous example, this argument
        would have been '45.0 65.0 78.0 55.0') while 'sum' is expecting
        numerical arguments.

More in the next part.
                          --- END of Part 2 ---


IV. Editor fundas
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How to display line numbers in VI/VIM/GVIM ?

 :set number    <- Displays the line numbers
 :set nonumber  <- Doesn't display the line numbers

A short form also exists for this command

 :set nu       <- Displays the line numbers
 :set nonu     <- Doesn't display the line numbers


V. Humour
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What is a Telescope ?

The telescope is in fact, an image transference device left to us by ancient
astronauts millions of years ago (MYA). When you look into the telescope, the
telescope uses an advanced aura-detection algorithm (ADA) which has cataloged
every possible genetic makeup of every human that has ever lived, been born or
is yet to be born and automatically attempts to adjust focus and lighting.
Unfortunately, the database was created MYA before the Gutenberg Press was
invented. The Gutenberg Press is solely responsible for humans requiring optical
support devices (OSD). So, that is why we must manually focus the telescope
every time we step up to it -- the aliens forgot to account for the printed 
word screwing our eyesight up.

Once the ADA has acquired your DNA coding and attempted to adjust for your
personal visual discrepancy (PVD), it sends a request out to the base station
in question via warped time/space (VWTS). The base station in turn, sends you
back it's favorite postcard-quality image through the warped time/space (WTS not
to be confused with VWTS) and you get an image. All celestial bodies including
nebula and black holes have base stations left by the aliens a gazillion years
ago (GYA).

Black holes, unfortunately, never developed an imaging device strong enough to
break through its gravitational pull so that is why you never see anything cool
when looking at a black hole.
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the focus of HDLPlanet on knowledge sharing, the information here could be just
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publishing of the newsletter. We don't guarantee the existence of the contents 
in the links all time.
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HDLPlanet Newsletter                                              Oct 2003