OP = 94
AF is unused and reserved. May be specified as an indirect field length. A literal flag will cause an Invalid Instruction (IEX = 21) fault.
BF is unused and reserved, but may be specified as an indirect field length.
A is the address of an IOCB. The address may be indexed, indirect or extended. The final address controller must be equal to UN or an Invalid Instruction (IEX = 03) fault will occur. The final address must be modulo 100 or an Invalid Instruction (IEX = 07) fault will occur.
The Start Physical I/O instruction makes an attempt to initiate an I/O to the I/O subsystem (IOS). If the I/O may be initiated, the instruction provides the necessary parameters to the IOS in an IOCB. The COMS are used to report the fact that the I/O has been initiated or not.
This instruction may only be executed with Privileged Enable set or an Invalid Instruction (IEX = 02) fault is reported.
The following checks are performed before initiating the I/O operation:
If a fault is detected, the I/O is not fired and the instruction is terminated with no further action.
If no fault is detected, an overflow check is performed on the I/O completion Queue and if an overflow is detected, the I/O is not fired and the Comparison Flags are set to HIGH.
If no overflow is detected, the I/O is fired and the comparison flags are set to EQUAL.
Set the Comparison Flags to HIGH if the I/O complete queue overflows, otherwise set them to EQUAL.
The Overflow Flag is not affected by this instruction.
Field overlap is not applicable to this instruction.