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Reference
SVC Routine
Code
Types
5
3,4
6
2,3,4
7
2,3,4
8
4
Reference Notes
• Register 5 contains the address of the super-
visor request tlock (SVRB), if a type
2,
3,
or
4 SVC routine is in control.
If a type 1
SVC routine is in control,
register
5
con-
tains
the address of the last active request
tlock.
• Register 6 through 12
contain
unpredictable
information.
•
Register
13 contains the same information as
when the SVC routine was called.
•
Register 14 contains the return address.
•
Register 15 contains the same information
as
when the SVC routine was called.
You
must
use registers 0, 1, and 15 if you want
to pass inforrr.ation to the calling program.
The
contents
of
registers 2 through 14 are restored
when control is returned to the calling
prograrr.
Because
relocatatle
address
constants
are not
relocated when a type
3
or
4
SVC
routine
is
loaded
into main storage, you cannot use them in
coding these routines; nor
can
you
use
macro-
instructions whose expansions contain relocatable
address
constants.
Types
1
ana
2
are
not
affected
by this restriction since they are part
of the resident control program.
You can extend the SVRB,
in
8-byte
increments,
from 96 bytes up to 144 bytes.
The extended area
is
available
as a work area during execution of
your routine only if you
specify
the
extension
during
the system generation process.
When your
SVC routine receives control, register 5 contains
the address of the SVRB
to
which
the
extended
save area is appended.
You
cannot
issue
the
WAIT
macro-instruction
unless
you have changed the system mask to allow
I/O and
external
interruptions.
If
you
have
allowed
these
interruptions, you can issue WAIT
macro-instructions that await
either
single
or
multiple
events.
The event control block (ECB)
for single-event waits or the ECB list
and
ECBs
for
mUltiple-event waits must be in dynamic main
storage.
When you issue an
XCTL
macro-instruction
in
a
routine
under
control of a type 4 SVRB, the new
load module is brought into a transient area.
The
contents
of
registers
2
through
13
are
unchanged
when
control
is
passed
to the load
module; register 15 contains the entry
point
of
the called load module.
Adding SVC Routines to the control Progran:
35
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