Columbia Kermit/kermit.zip/c/ucmicro.doc

Text File | 2020-01-01 | 5KB | 110 lines

     KERMIT UCMICRO is a modification  of  KERMIT  UCSD  (UCTERAK  version)
written  by  Kate  MacGregor of Cornell University.  UCMICRO was created by
Tim Shimeall of the University of California, Irvine, to run on  a  Western
Digital  Pascal  Microengine.   Rather widespread, but superficial, changes
were made in the translation from UCTERAK to UCMICRO KERMIT.  This  version
of KERMIT is written entirely in UCSD Pascal, version III.0, under the Vol-
ition Systems operating system.  It should work on any Pascal  Microengine,
since no version-dependent features were used.

     The following files make up KERMIT UCMICRO:
kermit.text - Main program (declarations, show, set  and  connect  commands
              with  file  inclusion  commands  to  bring in the rest of the
              files)
wdforw.text - "forward" declarations for routins in wdprocs.text
help.text - segment procedure to provide on-line assistance
sendsw.text - segment procedure to send files
recsw.text - segment procedure to receive files
parse.text - segment procedure to parse user commands
wdprocs.text - Pascal Microengine specific device drivers
utils.text - general utitility functions
rsutils.text - utitility functions shared by recsw and sendsw segments
help.doc - this file.

In the Kermit distribution, the .TEXT files are concatenated together
into a single file, UCMICRO.PAS.  In this file, each file begins with
a line like {>>>> name}, as follows:

{>>>> KERMIT.TEXT}
{>>>>WDFORW.TEXT}
{>>>> HELP.TEXT}
{>>>> SENDSW.TEXT}
{>>>> RECSW.TEXT}
{>>>> PARSE.TEXT}
{>>>>WDPROCS.TEXT}
{>>>>UTILS.TEXT}
{>>>>RSUTILS.TEXT}

The Pascal Microengine has the UCSD  P-System  interpreter  implemented  in
microcode.   It  therefore has no accessible assembly language, so routines
that were done in assembler under the UCTERAK version had to be  redone  in
Pascal  for  the  UCMICRO  version.  These routines were adapted from a set
written  by  Tim  Shimeall  for  PCNET,  and  are  contained  in  the  file
"wdprocs.text".   Further,  the Microengine is not interrupt-driven, so the
"input queue" approach taken in the UCTERAK version had to be  replaced  by
polling  in  the UCMICRO version.  Once operating, the program had two per-
sistant problems: a) it would run out of memory,  causing  a  program  halt
after each file send and receive, and b) it wouldn't wait long enough for a
packet to arrive.  To free up more memory during file transfers,  the  com-
mand  parser  was  converted  from  a  "unit"  (seperately compiled library
module) to a "segment procedure" (overlay  segment).   The  UCTERAK  KERMIT
version  used a retry counter for packet timing.  The retry limit specified
only allowed for a 1 second tolerance on the Pascal Microengine (a Microen-
gine  is  about  4  times  faster  than  a  Terak).  UCMICRO has a machine-
dependent package timeout feature, using a retry counter in a loop of known
duration as a clock.

     UCMICRO has the following limitations:
   a) No wild card designations of file names
   b) No eight-bit file quoting
   c) No character repeat counts
   d) No '?' and <esc> at the end of a command line.
   e) No server communications
   f) Sending and receiving cannot be done on anything but .TEXT files  (which
      contain  a  two  block  header  and  space compression codes, and are
      divided into two-block "pages" which are padded with nulls to  ensure
      an integral number of lines in each "page").
   g) Only one file is sent at a time (a  break  packet  is  sent  after  each
      file).

     KERMIT UCMICRO has been thoroughly tested in  connections   with  UNIX
KERMIT,  but errors may persist.  In particular, since polling has replaced
interrupts in this version, characters may occasionally be lost.   However,
character loss has NOT been observed during testing of the final version of
KERMIT UCMICRO.

     The commands recognized by KERMIT UCMICRO are the same  as  those  for
KERMIT UCTERAK.

Another limitation on UCSD-KERMIT (shared between UCTERAK and the UCMICRO
version): Each line in the file received can be no longer than 80 characters.
There's a "quick fix" for this, but since I hope to make the file transfer
capacity more general later on, I'll just list the fix here:

To make the maximum length 255 chars instead of 80:

  1) delete the first two statements and the declarations of
     the variables 'ls:integer' and 's:string' from the
     procedure "bufemp" in the file RSUTILS.TEXT
  2) Add the following two statements to the procedure
     "initialize" in the file KERMIT.TEXT:
       s:=''; (* note: two single quotes with nothing between *)
      ls:=0;
  3) change the declaration of "s:string" near line 129 of the
    file KERMIT.TEXT to
      s:string[255];
  4) add the following line immediately after the declaration of
     "s:string[255]" (line 129 of KERMIT.TEXT):
      ls:integer;

What this does is to move "s" and "ls" (length of s) out to become
global declarations ("s" is otherwise unused), and to expand "s"'s
maximum length to 255 (maximum allowed by UCSD).

As I said, I hope to make a more general file transfer mechanism soon
(which will permit data and code files to be transferred as well as
text), but "soon" can be a relatively long period of time.

Maybe this fix can also be made to the other UC versions of kermit.
                Tim