🚀 go-pugleaf

>Sorry if this is a silly question, but is there a good source for system
>calls on an IBM370?  We've been using the ASSIST macros, but I am also
>interested in knowing what the actual methods are (ie: how do I *really*
>output to the screen or get a character :)

  If your operation system is VM/CMS it is very convenient to study how
  do virtual machine  *realy* makes input and output. VM emulates all
  I/O operations as it described in S-370 principles of operation.

  CMS has a few levels to organize I/O for users program, but as it
  runs in (virtual) supervisor mode all privilege operations including
  SIO are available to programmer. So you can write your own CCW and
  run it. If you only interesting what CMS does, you can trace SIOs and
  SVCs.

  CMS also helps user to handle interrupts from various (virtual)
  devices in case I/O operation have finished normally or with errors.
  If you do not wish any interference (such as interrupt handler) you
  can run your program in standalone mode (use 3CARD LOADER file with
  object deck of your program for ipl-ing from virtual card reader).

  Now a few words about entering characters from terminal. There are
  two cases. First is when CP emulates a typewriter device as x'009'
  or x'01f' virtual console. In this case CMS performs more or less
  ordinary I/O operations using SIOs.

  The second way to run I/O at the terminal is so called fullscreen
  method which use DIAGNOSE calls of CP. It is impossible for CMS to
  use it's console in fullscreen mode directly by using SIOs, because
  x'009' or x'01f' is emulated typewriter. In this case CMS or any
  other program running at virtual machine needs an assistance of CP.
  It can use DIAGNOSE to "attract attention" and to "ask" CP to perform
  various functions, to start CCWs on discs, tapes and terminals and so
  on.

  But in both cases (typewriter and fullscreen) S-370 do not support
  character-by-character way of input/output (for any devices). All
  I/O activity starts after pressing "ENTER" which produces an interrupt
  Then the whole line, screen or only modified fields of the screen
  will be entered.

  If you *realy* need to realize character-by-character method, I think
  it is possible to do using CCWs with PCI flag. But I think it is
  better not to do without severe necessity.

Best regards, Andrew Ananjev, Head of software support group.
Space Research Institute (IKI), Moscow. Phone: +7-095-333-24-02