[Info-vax] BASIC and AST routines

[VAXman- at SendSpamHere.ORG]

In article <sn8nrg$g7b$1 at dont-email.me>, Dave Froble <davef at tsoft-inc.com> writes:
>On 11/19/2021 6:43 AM, Bob Gezelter wrote:
>> On Friday, November 19, 2021 at 12:35:24 AM UTC-5, Dave Froble wrote:
>>> On 11/18/2021 10:49 PM, Bob Gezelter wrote:
>>>> On Thursday, November 18, 2021 at 8:08:47 PM UTC-5, Chris Townley wrote:
>>>>> On 18/11/2021 23:31, Bob Gezelter wrote:
>>>>>> On Wednesday, November 17, 2021 at 6:14:30 PM UTC-5, John Doppke wrote:
>>>>>>> So I've been playing with writing AST routines (stubbornly) in BASIC. They work ok, but I've found I have to declare the routine as having 5 'standard' parameters - "function long AST long (p1, p2, p3, p4, p5)". I'm not sure what the 5 parameters 
>>>>>>>
>>>>>>> Now I need an AST for a call that requires a parameter - SMG$ENABLE_UNSOLICITED_INPUT. I've tried adding a parameter in my usual list in different ways but I can't get it to work. Every time it's called I get a reserved opcode exception. (A DCLAST
>>>>>>>
>>>>>>> Can anyone shed some light on what the parameters are that BASIC is getting? I'll probably end up writing this one in MACRO, but I want to understand what is happening.
>>>>>>>
>>>>>>> -John
>>>>>> John,
>>>>>>
>>>>>> Been there, done that (for a client whose entire codebase was written in BASIC).
>>>>>>
>>>>>> As VAXman and Dave Froble noted, the five parameters are passed are, and I quote from David's posting:
>>>>>>
>>>>>> "From the 7.3 docs:
>>>>>>
>>>>>> Table 8–3 AST Arguments for VAX Systems and Alpha Systems
>>>>>> VAX System Arguments Alpha System Arguments
>>>>>> AST parameter AST parameter
>>>>>> R0 R0
>>>>>> R1 R1
>>>>>> PC PC
>>>>>> PSL PS "
>>>>>>
>>>>>> One will notice that the correct number of parameters restriction does not appear in all languages. C , FORTRAN, and others have looser restrictions on parameter lists, as well as variable-sized parameter lists. BASIC does not. BASIC requires that 
>>>>>>
>>>>>> Many library routines can be called from both normal thread and AST contexts, but since many of the library routines are not- re-entrant, one cannot generally call library routines from both AST and process threads. However, most OpenVMS general li
>>>>>>
>>>>>> As to what is the AST parameter, my general practice is to use a data structure for each file, and pass a pointer to that file as the AST parameter. That allows storage of useful information beyond the file number/handle.
>>>>>>
>>>>>> - Bob Gezelter, http://wwww.rlgsc.com
>>>>>>
>>>>> IIRC Basic can handle variable number of parameters when calling a
>>>>> sub/function, but you cannot write them in Basic
>>>>>
>>>>>
>>>>> --
>>>>> Chris
>>>> Chris,
>>>>
>>>> Not relevant. I the case referenced, the AST, written in BASIC, is the CALLED routine. As to what can be called from BASIC, I suggest reading the reference manual. As I recall, the original header files had no parameter definitions, so it was possibl
>>>>
>>>> Of course, more than a few people did not pick up the change and continued the earlier approach, which leads to problems.
>>>>
>>>> - Bob Gezelter, http://www.rlgsc.com
>>>>
>>> I'm going to confess to curiosity. Why are R0, R1, SP, and PC passed to an AST
>>> routine?
>>> --
>>> David Froble Tel: 724-529-0450
>>> Dave Froble Enterprises, Inc. E-Mail: da... at tsoft-inc.com
>>> DFE Ultralights, Inc.
>>> 170 Grimplin Road
>>> Vanderbilt, PA 15486
>> David,
>>
>> Am rather busy this morning, but the IDSM has a full description of the dispatching process for an AST.
>>
>> - Bob Gezelter, http://www.rlgsc.com
>>
>
>Oh, you mean that big book on the bookshelf gathering dust?
>
>Got to now consider how curious I really am.

RTFM!

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