VMBLOK VCHBLOK VCUBLOK The address of the VMBLOK is in general register 11.
Examine the following VMBLOK fields:
1. The virtual machine running status is contained in VMRSTAT (displacement
X'5S'). The value of this field indicates the running status.
2. The virtual machine dispatching status is contained in VMDSTAT (displace­
ment X'59'). The value of this field indicates the dispatching status.
3. Examine the virtual PSW and the last virtual machine privileged instruction.
The virtual machine PSW is saved in VMPSW (displacement X'AS') and the
virtual machine privileged or tracing instruction is saved in VMINST (dis­
placement X'9S').
4. Find the name of the last CP command that executed in VMCOMND (dis­
placement X'14S').
5. Check the status of I/O activity. The following fields contain pertinent infor­
mation.
a. VMPEND (displacement X'63') contains the interrupt pending summary
flag. The value of VMPEND identifies the type of interrupt.
b. VMFSTAT (displacement X'6S') contains the virtual machine features.
c. VMIOINT (displacement X'6A') contains the I/O interrupt pending flag.
Each bit represents a channel (0 through 15). An interrupt pending is indi­
cated by a 1 in the corresponding bit position.
d. VMIOACTV (displacement X'36') is the active channel mask. An active
channel is indicated by a 1 in the corresponding bit position.
The address of the VCHBLOK table is found in the VMCHSTRT field (displace­
ment X'IS') of the VMBLOK. General register 6 contains the address of the
active VCHBLOK. Examine the following fields:
1. The virtual channel address is contained in VCHADD (displacement X'OO'). 2. The status of the virtual channel is found in the VCHSTAT field (displacement X'06'). The value of this field indicates the virtual channel status.
3. The value of the VCHTYPE field (displacement X'07') indicates the virtual
channel type.
The address of the VCUBLOK table is found in the VCUSTRT field (displacement
X' 1 C') of the VMBLOK. General register 7 contains the address of the active VCUBLOK. Useful information is contained in the following fields:
1. The virtual control unit address is found in the VCUADD field (displacement X'OO'). Introduction to Debugging 513

VDEVBLOK RCHBLOK
2. The value of the VCUSTAT field (displacement X'06') indicates the status of
the virtual control unit.
3. The value of the VCUTYPE field (displacement X'OT) indicates the type of
the virtual control unit.
The address of the VDEVBLOK table is found in the VMDVSTRT field (dis­
placement X'20') of the VMBLOK. General register 8 contains the address of the
active VDEVBLOK. Useful information is contained in the following fields:
1. The virtual device address is found in the VD EV ADD field (displacement X'OO'). 2. The value of the VDEVSTAT field (displacement X'06') describes the status
of the virtual device.
3. The value of the VDEVFLAG field (displacement X'07') indicates the
device-dependent information.
4. The VDEVCSW field (displacement X'08') contains the virtual channel status
word for the last interrupt.
5. The VDEVREAL field (displacement X'24') contains the pointer to the real
device block, RDEVBLOK.
6. The VDEVIOB field (displacement X'34') contains the pointer to the active IOBLOK. 7. For console devices, the value of the VDEVCFLG field (displacement X'26')
describes the virtual console flags.
8. For spooling devices, the value of the VDEVSFLG field (displacement X'2T)
describes the virtual spooling flags.
9. For output spooling devices, the VDEVEXTN field (displacement X'10') con­
tains the pointer to the virtual spool extension block, VSPXBLOK. 10. The value of the VDEVFLG2 field (displacement X'38') describes the
Reserve/Release flags and other miscellaneous conditions.
11. For Reserve/Release minidisks, VDEVRRB (displacement X'3C') contains
the address of the VRRBLOK.
The address of the first RCHBLOK is found in the ARIOCH field (displacement
X'3B4') of the PSA (Prefix Storage Area). General register 6 contains the address
of the active RCHBLOK. Examine the following fields:
1. The real channel address is found in the RCHADD field (displacement X'OO'). 2. The value of the RCHSTAT field (displacement X'04') describes the status of
the real channel.
514 VM/SP System Programmer's Guide