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From: cdash@boulder.Colorado.EDU (Charles Shub)
Newsgroups: comp.unix.questions,comp.edu,comp.lang.misc
Subject: Student friendly assemblers
Message-ID: <663@boulder.Colorado.EDU>
Date: Sun, 17-May-87 23:38:07 EDT
Article-I.D.: boulder.663
Posted: Sun May 17 23:38:07 1987
Date-Received: Mon, 18-May-87 03:51:59 EDT
References: <351@aucs.UUCP> <588@maccs.UUCP> <234@brandx.rutgers.edu> <593@maccs.UUCP> <6725@mimsy.UUCP>
Reply-To: cdash@boulder.Colorado.EDU (Charles Shub)
Organization: University of Colorado at Colorado Springs
Lines: 59
Xref: mnetor comp.unix.questions:2375 comp.edu:388 comp.lang.misc:399

In article <6725@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
>In article <593@maccs.UUCP> ns@maccs.UUCP (Nicholas Solntseff) writes:
>> [ discussion of assembly options in a unix environment portions deleted ]
>
>>and did not really address the problem of sophomore students learning
>>a very user-unfriendly assembler.
>
>Okay, here is the *real* question:
>What makes an assembler friendly or unfriendly?
>I have used:
>	[ list deleted ]
>Of all of these, I like the 4BSD and Sun `as' best, for two reasons:
>the 4BSD assembler is fast, and the Sun assembler is reasonably fast
>except for extremely large (compiler generated) inputs; and both of
>them support a form of temporary labels (4BSD has number labels, Sun
>has both number labels and short-scope labels).
>
>So what is /bin/as missing, or what does it do wrong, that makes it
>user-unfriendly?

The biggest problem students, especially sophmores, face is that they
need simplicity!!!! That means either some simple system calls like
INCHWL on TOPS-20 assembler (input character, wait for line feed before
returning) or macros (see almost any assembly text book) like read_w to
read in word length integers. Students need to be able to write 20 to 30
line programs that do something reasonably useful. I have taught the 
machine organization and/or symbolic language programming course at several
universities for almost 20 years using GE Macro Assembly Processor, Xerox Macro
Assembly Program, TOPS-20 Macro, Vax Macro-11 under VMS, and IBM 360 BAL. I
have also used a home grown processor for MIXAL [knuth, 1969] and several
others. User friendly items include at least:
1. same mnemonic for adding (et. al.) irrespective of whether the operands 
   are registers or memory cells
2. being able to give symbolic names (other than Rn) to registers.
3. identical syntax for accessing an address in either a memory cell or a
   register.
4. reasonable vehicles for parameters in macro definitions (an avid hater of
   ampersands here) for both positional and keyword parameters.
5. a reasonable selection of conditional assembly pseudos
6. EXCELLENT error diagnostics because students WILL make errors
7. good literal or remote assembly features so data can be written near the
   code using it (tops 20 was excellent about this) so students can invoke a
   print system call or macro and have what is being printed at the print
   statement rather than in a data block.
8. reasonably free form input (this was a problem way back when)
9. a good selection of pseudos for data generation and storage allocation
   that match the machine architecture. (I seem to recall one from the distant
   past that had an ARRAY pseudo that defined the symbol as 1 word less than
   the next free location so that if you put a 1 in a register and used indexing
   you got to the first reserved space. This was back before PASCAL so it was
   what the fortran programmers wanted to do)
10. A user friendly listing so students can see what is happening.

I could go on a while, but this is getting long enough already.
-- 


cdash   aka cdash@boulder.colorado.edu    aka ...hao!boulder!cdash
	aka ...nbires!boulder!cdash