pc-tools/ldc2/doc/intro.tex

   1 \section{Introduction}
   2 \subsection{Motivation}
   3 Software for the Honeywell Series 16 minicomputers is very rare today,
   4 most of the software ever written for them seems to be lost. But some
   5 of it still exists --- spread over the world in dusty boxes on attics or in
   6 cellars, on software preservation websites and on collectors' harddisks.\\
   7 The software is stored on punched paper tapes or in disk files containing images
   8 of paper tapes.\\
   9 Often enough the tape labels (resp. file names) are way too vague to exactly
  10 identify and understand the contents of a tape.\\
  11 Back in the
  12 times when the Series 16 machines were still in use, everybody knew
  13 \emph{his} paper tapes' contents and \emph{his} programs' library dependencies.
  14 Everybody had an I/O library for \emph{his} computer's configuration.\\
  15 Nowadays we have only the remains of all that: many object and library tapes
  16 with sometimes obscure names written on it.\\
  17 We can neither verify the correctness of the data on the tapes nor
  18 get any information about a tape's exact contents, exported symbols,
  19 and dependencies.\\
  20 So there is a need for the collector to verify, analyze, sort, split, and
  21 recombine his paper tape software.\\
  22 The \pname program provides a handy approach to
  23 help doing this using a newer computer with an UNIX style operating system,
  24 disk drives, and some kind of paper tape reading facility.
  25
  26 \subsection{The Technical Background}
  27 The Honeywell Series 16 assembly program DAP-16 \cite{ser16:dap16:manual}
  28 and the FOTRAN IV compiler program \cite{ser16:frtn:manual}
  29 read source code from punched paper tape and translate it into relocatable
  30 object code which is then punched out on paper tape again.
  31 See \cite{ser16:progref} for operation details.\\
  32 The object data is organized in blocks of variable layout and length consisting
  33 of 16 bit wide native machine words. The block format is described
  34 in \cite{ser16:progref}, pages 5-21ff. \\
  35 To store the object blocks on punched paper tapes, each word in the block is
  36 divided into three parts: the first one is 4 bits wide, the second and
  37 third one are 6 bits wide.\\
  38 Each frame is now translated so that the resulting paper tape frames don't
  39 contain any printable or control characters. Then the block is enclosed by
  40 control characters and sent out to the paper tape punch device.\\
  41 The resulting ''silent 4/6/6 code'' can be easily processed by the ASR 33
  42 printing terminal. It is even possible to mix listing and object code
  43 on one tape because the text between the silent data blocks is
  44 ignored by the loader.\\
  45 See \cite{ddp516:users_guide}, page 10-1ff for more information about this
  46 concept, but be aware that the translation table in the document contains
  47 \emph{severe} errors.\\
  48
  49 \subsection{Functional Overview}
  50 \pname is a program which is capable of analyzing object tapes.\\
  51 It reads in the data from a file or a serial line, retranslates
  52 the mangled characters, and reassembles the data blocks into an internal
  53 representation.\\
  54 The block checksum is checked immediately after a
  55 block has been read in. This provides for immediate error reporting and
  56 handling. One input data error handling possibility is to immediately
  57 stop a tape reader connected to a serial port so that the user has a clue
  58 where to look for faulty regions on the paper tape. This is very useful
  59 when reading in last existing copies of old software.\\
  60 After the error-free blocks are present in the program's memory, it is
  61 possible to do various operations on it. Examples are extracting and
  62 listing of symbol names, split up the data of a library into several files
  63 or even reverse assembly and relocating into a virtual Series 16 main memory
  64 (not in the base variant of the program).