April 1,1981
The following chart lists theDIAGNOSE Code X'24', the meaning
registers where data is returned• cond ition
of each
codesCP can return
condition code, and.-- I , This register
contains information, If the condition
codeequals Ry Ry+i2 Comments o x x
2 x x
3X INormal completion I Undefined IThe virtual device
lexists but is not
lassociated with aIreal device I Invalid device
laddress or theIvirtual device Idoes not exist
lTheEx register contains information only when DIAGNOSE Code X'24' specifies a virtual console whose address in unknown.
2If Ry is register 15,CP returns only virtual device infor
mation: no information is returned in register Ry+1.DIAGNOSE Code X'28' -- Channel Program
Modification
,
for
theDIAGNOSE Code X'28' allows a virtual machine to correctly execute some
channel proqrams modified after theStart I/O (SIO) instruction is
issued and before the input/output operation is completed. The channel
command word(CCW) modifications allowed are: • A Transfer in Channel (TIC) CCW modified to a No Operation (NOP) CCW • A TIC CCW modified to point to a new list of CCis • A NOP modified to a TIC CCW When a virtual machine modifies a TIC CCW, it is modifying a virtual
channel proqram.CP has already translated that channel program and is
waiting to execute the realCCws. The DIAGNOSE instruction, with Code X'28', must be issued to inform CP of the change in the virtual channel
program, so thatCP can make the corresponding change to the real CCW before it is executed. In addition, when a NOP CCW is modified to point
to a new list ofCCWs, CP translates the new CCWs. To be sure that the DIAGNOSE instruction is recognized in time to
update the realCCW chain, the virtual machine issuing the DIAGNOSE instruction should have a high favored execution value and a low
dispatching priority value. TheCP SET command should be issued: SET FAVORED xx SET PRIORITY nn
194IBM VM/370 SYstem Programmer's Guide
The following chart lists the
registers where data is returned
of each
codes
condition code, and
contains information
code
2 x x
3
lexists but is not
lassociated with a
laddress or the
lThe
2If Ry is register 15,
mation: no information is returned in register Ry+1.
Modification
,
for
the
channel proqrams modified after the
issued and before the input/output operation is completed. The channel
command word
channel proqram.
waiting to execute the real
program, so that
to a new list of
update the real
dispatching priority value. The
194