|OP||AF||BF||A Syllable||B Syllable|
OP = 85
AF Unused and reserved. Can be specified as an indirect field length. A literal flag causes an invalid instruction fault (IEX=21).
BF Variant, which can be specified as an indirect field length. The following variant can be specified:
The use of other BF values causes an Invalid Instruction fault (IEX=26).
The A Syllable which represents the initial descriptor can be indexed, indirect, or extended. The final address controller must specify UN or cause an Invalid Instruction fault (IEX=03). When checking the initial descriptor, the B-address can be equal to or greater than the A-address.
The B Syllable which represents resultant descriptor can be indexed, indirect or extended. The final address controller must specify UN or cause an Invalid Instruction fault (IEX=03).
|Note||This instruction can only be executed with the Privileged Enable toggle set, or an Invalid Instruction fault (IEX=02) occurs.|
CIO converts the relative type of information provided in the initial descriptor to the format required by the resultant descriptor, which is a subset of a full IOCB.
The format of the initial descriptor is:
|Memory Area Number||10-11|
The format of the resultant descriptor is:
|Buffer Begin Address||00-09|
|Buffer MAST Number||30-35|
|I/O Result Descriptor||76-113|
CIO examines the A- and B-addresses in the initial descriptor and checks that:
If CIO does not detect any faults, the overflow flag is reset, and the difference between the A- and B-addresses in the initial descriptor is placed in the “buffer size” field of the resultant descriptor.
CIO locates and resolves the destination entry by:
In addition to the checks within the procedures, CIO checks that:
If CIO detects no faults, the “buffer begin address” and the MAST number are written into their respective fields in the resultant descriptor.
If CIO detects that BF=01, the instruction is terminated.
If CIO detects that BF=00, the MAST entry associated with the I/O buffer memory area must be examined. The MAST number is an array subscript into the MAST that locates the MAST entry. CIO obtains exclusive access to the MAST entry and performs the following checks on the status digit field of the MAST entry:
The comparison flags are set if one of the following fault conditions is detected in the A or B addresses of the initial descriptor.
Also the comparison flags are set if the MAST entry associated with the I/O buffer is examined:
The overflow flag is set if one of the following fault conditions is detected in the A- or B-addresses:
Otherwise the overflow flag is reset.