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The Lights Keep on Blinken
cavac writes "At the 19th Chaos Communications Congress in Berlin/Germany developers showed their newest developments for the closed-down Blinkenlights-Project. One of the projects was the Blinkenlights Fileserver Project. Members of this team developed a protocol and some tools similar to ftp, which you can use to share Blinkenlights-Movies. Today, a first Beta-Version was released. You might want to check it out. (It also includes the famous Telnet-Blinkenlights-Player).
We are still searching people willing to help us developing this software even more or to work with us on "Phase II": Implementing Soft- and Hardware for a Hardware-Based Blinkenlights Player. This will most likely based on one of Zilog's new Development Kits - the "Z8 Encore!"."
What is Reverse Polish Notation?
When you are at school you learn that different arithmetic operators have different precedence, although that may not be the exact phrase the teacher uses. You are probably given a mnemonic such as "My Dear Aunt Sally" (meaning Multiplication, Division, Addition, Subtraction) to tell you the order in which to do sums. For example, if you are given:
1 + 2 x 3 = ?
you know to multiply 2 by 3 before adding the 1. Early pocket calculators were not acquainted with Aunt Sally, and would evaluate this expression as 9.
Another school-days mnemonic, BODMAS, tells us to attend to the bracketed expressions first, followed by the usual algebraic operator precedence. Brackets (or more properly parentheses) remove any ambiguity about the order of evaluation of expressions. Most complex expressions could not be expressed without brackets, and they are often used in computer programming even when they are not strictly required, simply to eliminate confusion. For example:
(1+2) x 3 = ?
is guaranteed to evaluate to 9, whatever precedence rules are applied (or if the programmer has forgotten them).
The BODMAS rule is applied recursively; brackets can contain other complex expressions which themselves contain brackets, and so on.
In the early days of electronic calculators these rules proved fiendishly difficult to implement in calculator hardware. But calculator designers at Hewlett-Packard realised that a radically different method of defining the arithmetic, invented in the 1920's by Polish mathematician Jan Lukasiewicz (1878-1956) for symbolic logic, could be used to simplify the electronics at the expense of a little learning by the user. In the 1960's that would be regarded as a reasonable trade-off. For most calculator users of the time, the alternative was the error prone practice of writing down intermediate results. The Hewlett-Packard engineers called their calculator logic Reverse Polish Notation (or RPN) in recognition of its inventor.
Using RPN, it is possible to express an arbitrarily complex calculation without using brackets at all. In RPN the simple example "(1+2) x 3" becomes:
3 2 1 + x
Like a sentence in German, all the verbs come at the end. This notation may look strange at first, and clearly if the numbers where entered as shown you would get the number three-hundred and twenty-one! To make a this work you need an extra key that tells the calculator when you have finished entering each number. On most RPN calculators this is called the "Enter" key and fulfills a similar function to an equals key on a conventional calculator but in reverse. So the example would actually be input as:
3 enter 2 enter 1 + x
This gives the correct answer, 9. If you wanted to work out "1 + 2x3" you would input this as:
1 enter 2 enter 3 x + (answer: 7)
You need to think of entering numbers as being like putting plates into one of those spring loaded plate stacking trolleys you get in canteens. Every time you enter a number, it is pushed onto the stack. When you eventually start using arithmetic operators, numbers start "popping" off the stack as needed. You can also push more numbers onto the stack. At the end of the calculation you will have "used up" all the numbers and the stack will be empty.
A calculator using conventional logic will internally convert the expression to the RPN form above. This may be achieved by parsing the bracketed expression before carrying out the calculation. But more likely the calculator logic will be pushing numbers down onto the stack every time a pair of brackets is opened or is implied by the operator precedence. So in effect an RPN calculator is offloading this work to the calculator user, resulting in simpler logic design in the calculator. Nowadays the design issues of using conventional bracket notation in an electronic calculator are trivial, and yet users of RPN calculators rarely seem to want to move over to the more conventional algebraic logic. Although RPN seems strange to the uninitiated, people who overcome the initial hurdle find it a powerful and elegant tool which is ultimately easier to use. Luckily for RPN devotees, Hewlett-Packard continues to develop RPN calculators, such as the HP32 and some of the latest models have the capability of both RPN and algebraic logic. And of course Calc98 also supports RPN as a user configurable option.
OMFG FIRST POST
Anyone who have ever used a few microcontrollers know that PIC Micro's reign supreme. Why, there have been several webservers built using tiny SM 8 pin chips!
Z8's are just a resharshed version of the X8 with onboard memory and a serial port. Their preformance sucks. 577.6 kHz in this day and age? C'mon.
To conclude:
Z8, x86, AVR, 8051 == crap
PIC == Good
PIC's are great!
PS: Michael "censorware.org" Sims, you should apoligise for mentioning Z8's. They are an embarrasment to us all.
Phase II: Implement Soft- and Hardware for a Hardware-Based Blinkenlights Player.
Phase III:
Phase IV: Profit.
U.S. Decision On Iraq - How Policy Was Set
By Glenn Kessler Washington Post Staff Writer (Sunday, January 12, 2003; Page A01)
On Sept. 17, 2001, six days after the attacks on the World Trade Center and the Pentagon, President Bush signed a 21/2-page document marked "TOP SECRET" that outlined the plan for going to war in Afghanistan as part of a global campaign against terrorism.
Almost as a footnote, the document also directed the Pentagon to begin planning military options for an invasion of Iraq, senior administration officials said.
The previously undisclosed Iraq directive is characteristic of an internal decision-making process that has been obscured from public view. Over the next nine months, the administration would make Iraq the central focus of its war on terrorism without producing a rich paper trail or record of key meetings and events leading to a formal decision to act against President Saddam Hussein, according to a review of administration decision-making based on interviews with more than 20 participants.
Instead, participants said, the decision to confront Hussein at this time emerged in an ad hoc fashion. Often, the process circumvented traditional policymaking channels as longtime advocates of ousting Hussein pushed Iraq to the top of the agenda by connecting their cause to the war on terrorism.
With the nation possibly on the brink of war, the result of this murky process continues to reverberate today: tepid support for military action at the State Department, muted concern in the military ranks of the Pentagon and general confusion among relatively senior officials -- and the public -- about how or even when the policy was decided.............
Read the full article here - How U.S. Policy On Iraq Was Set