SYSLESS

Adding or changing special system lessons in SYSLESS

The site system lesson list ¹⁾ sometimes needs to be modified to confer special abilities and authorize reserved commands to be used.

There are two ways to add or modify the characteristics of a system lesson.

1. Change the content of code file *sysless* (via *plmods* currently)
2. Use lesson *s0syslst*

The *sysless* method is to be used the add lessons considered to be core to the operation of the system - release lessons.

The *s0syslst* can be used for site specific lessons, personal work spaces, temporary testing, and the like.

Lessons may NOT be on both lists.

In *sysless*, lessons must be kept in alphabetical order. See the case study below for an example entry.

At system load time the files from s0syslst and sysless are merged into a single list. This happens early on in lesson s0init with this line

do      sysless         $$ system lesson table

Unit sysless is used from lesson s0syslst.

Up until 11/16/2023 the procedures described below were necessary the “effectuate” lessons added in syslees. This was due to an oversight in s0syslst unit sysless. That problem has now been corrected and discussed below in the next section.

Prior to this date the code in unit sysless of lesson s0syslst did these basic things

1. Read the table of release system lessons from sysless in EM
2. Copy the lessons from s0syslst to the top of a new copy of what will become the final system lesson table
3. Copy the release system lessons from a “cache” common
4. Resort the entire merged list
5. Write the new merged / sorted list to the EM system lesson table

Unfortunately new or changed lessons from sysless were not put into the cache common and were ineffective. But a fix was possible. The new basic action of unit sysless is:

1. Read the table of release system lessons from sysless in EM
2. Copy the sysless entries to the “cache” common
3. Copy the lessons from s0syslst to the top of a new copy of what will become the final system lesson table
4. Copy the release system lessons from a “cache” common
5. Resort the entire merged list
6. Write the new merged / sorted list to the EM system lesson table

The following lines 5-8 were added to unit sysless

 1  do      loadov          $$ and load into EM
 2  *
 3  calc    lslots := int(nlsnwds/2)  $$ slots
 4  *
 5  if      not(editor)     $$ need to update common with EM
 6  .       calc    nless := int((sltlen - 202) / 2)
 7  .       transfr rlesbuf(1);rsyslsn(1);sltlen-202
 8  endif
 9  *
10  *
11  branch  (nless+nlocal) > lslots,2many,x
12  *
13  ***     zero sysless buffer
14  zero    lesbuff(1),nlsnwds
15  *
16  * move lessons from local list to sysless buffer

In order to give system lesson notesys WRT (read/write CM/ECS permission) the line in COMPASS deck SYSLESS that reads:

 LTYPE  NOTESYS,(BIN,SYS,D2,SYSNV) 

must be changed to

 LTYPE  NOTESYS,(BIN,SYS,WRT,D2,SYSNV)

What is expected is that the macro LTYPE fills out a table in the SYSLESS overlay that is referenced to check system lesson permissions.

Assembling changes into the SYSLESS overlay is insufficient to create the desired effect. This is due to the common s0syslist in tutor file sysfile overriding the parameters specified in the SYSLESS overlay. This common is (effectively) an operational cache that not only contains a copy of the previous SYSLIST overlay values, but also the local site system list cache. During initialization, the contents of the common replace the values in EM ²⁾ this special overlay via a callout from s0init (using code from s0syslst).

In addition to making the required edits to the SYSLESS overlay, there are two ways to fix the sysfile caching problem.

ALWAYS edit deck SYSLESS and do a new build for released system lesson list changes.

If SYSLESS is not properly modified, the “REFRESH” method will not work. The “Temporary Method” will only work if no new system lessons were added to SYSLIST.

It is possible to modify the common directly using the knowledge provided in the overview. This is risky but if the system lesson already exists you can find it in the proper portion of the common.

The layout of the common as of this writing is:

 Common layout:
 
      buffer address  buffer description
      --------------  ------------------
      0001 - 0100     header information
      0101 - 0220     local system lessons
      0221 - 1280     release system lessons

In the example, we located the released system lessons (containing test case NOTESYS) starting at word 321. The format of the common is (essentially) a collection of lesson names followed by a word with bits set for the lesson permissions.

Once a proper backup has been taken:

1. Back out all active users before editing the common
2. Using maintenance credentials in group p
   1. Enter file sysfile and access common s0syslst
   2. Abort the common (this prevents the system's resident portion of the common in EM ³⁾ from overwriting the changes.
   3. Edit the commmon
3. Shut Down PLATO
4. Restart PLATO and check the lesson permissions using lesson s0syslist option 1.

In system lesson s0syslst, the built in common validation utility may be used to refresh the cached common ⁴⁾. This option is recommended method for lessons added to the SYSLESS deck and will re-write the released lesson portion of the common file.

As a group s records user:

1. Invoke lesson s0syslst
2. Press SHIFT-DATA for special options.
3. Select option 1 to disable local modifications.
4. Press SHIFT-HELP to disable local modifications..
5. Press BACK twice to return to the SYSTEM MODE page.
6. Press SHIFT-STOP to sign off.
7. Shutdown PLATO and NOS in the normal manner.

At this point, the system should be re-started with the modified deadstart tape containing the modified SYSLESS PLATO overlay.

1. During initialization of control point PLA1, you will not see the usual LOCAL SYSTEM LESSONS INSTALLED message on the console.
2. Log in to CYBIS using group s records.
3. Invoke Lesson s0syslst
4. Press SHIFT-DATA for special options.
5. Select option 3 Run common verification utility.
6. Press SHIFT-HELP to update common information.
   This step updates the common from the SYSLESS version of the system lessons. Local lessons lists will be preserved.
7. Press BACK to return to the main System Lesson List Management Utility page.
8. Select option 1 Check options assigned to a lesson, and verify that the desired system lesson is recognized and has the expected permissions.
   

In our example - we were seeking the wrt attribute on lesson NOTESYS.

1. Press BACK to return to the main System Lesson List Management Utility page.
2. Press SHIFT-DATA to get to Special Options.
3. Select option 1 Enable local modifications.
4. Press SHIFT-HELP to re-enable local system lessons.
5. Restart CYBIS.

The system should come up with all the local system lessons + the new SYSLESS settings from deck SYSLESS.