See (p2,gtt) for Tymnet access via VM's Tymnet base. See (p2,tymnet) for a description of the only program that we now expect to use the TLBA key.

This key provides access to a read device and a write device connected to a "Lemcom" Tymnet base.

Each device is either (_working) or not. {It is an exercise for the student to determine the relationship of this definition to IBM subchannel terminology.} The device becomes working when an I/O operation for that device begins. The device becomes not working when the device signals the completion of the operation.

A flag called "wait end" is initially off. It is turned on by an "interesting event" and by the "abort wait" operation. It is turned off when a wait completes with return code 0 or 2.

A flag called "polling" is initially off. It is turned on by the "start poll" operation and is turned off by the "abort poll" operation and by an "interesting event".

An "interesting event" is one of the following:

An "interesting termination" of the write device;

An "interesting termination" of the read device;

An "abort poll" operation is done while both devices are not working {i.e., during the 0.2 second delay of the polling cycle}.

An "interesting termination" of a device is one of the following:

The device produces a condition code 1 or 3 on a SIOF.

The device becomes not working {i.e., interrupts} and there is an error. There is an error on the write device if any status bits are on besides channel end and device end. There is an error on the read device if any status bits are on except channel end, device end, and the datacount.

The device becomes not working {i.e., interrupts} and the other device is also not working and:

polling is off, or

the read data is not the six bytes 0, 255, seq, 2, seq, 2.

For each operation below, if rtod is not equal to restart-tod, c=1 and the string (8, restart-tod), (8, cpuid) is returned. Restart-tod is the time-of-day {in STCK format} when Gnosis was restarted. {Actually, it would be the time after which nothing that was done has been undone.}

TLBA(0, (8, rtod); ==> c, string;) "Start read"

If the read device is already working, c=2. If polling is on, c=3. Otherwise, a SIOF for a read CCW for up to 406 bytes is done to the read device and c=0.

If the write device is already working, c=2. If polling is on, c=3. If ldata > 2044, c=4. Otherwise, a SIOF for a write CCW to write the data is done to the write device and c=0.

If the read device is already working, c=2. If polling is on, c=3. Otherwise, a SIOF for a sense CCW for up to 406 bytes is done to the read device and c=0.

If the write device is already working, c=2. If polling is on, c=3. Otherwise, a SIOF for a sense CCW for one byte is done to the write device and c=0.

If the read device is not working, c=2. Otherwise, a HDV is done to the read device and c=0.

If the write device is not working, c=2. Otherwise, a HDV is done to the write device and c=0.

If there is already a wait operation in progress, c=3. Otherwise, this operation waits until the endwait flag is on {which may be immediately} and then turns it off and returns string = (1, seq), (write-status), (1, byte from the last write sense operation), (read-status). C = 0 if polling is off, 2 if it is on.

Seq is described under polling, below. It is significant only if polling was on.

Write-status is:

If the write device is working: (5, 0)

If the write device is not working because the 0.2 second delay of a polling cycle is in progress: (1, 4) (4, not applicable)

If the write device is not working because the last SIOF returned condition code 3:

.(1, 3)

.(4, 0)

Otherwise:
.(1, 2-bit condition code from SIOF (0 or 1))

.(1, unit status) (will have channel end and device end bits on)

.(1, channel status)

.(2, residual count)

Read-status is:
If the read device is working: (5, 0)

If the read device is not working because the last SIOF returned condition code 3:

.(1, 3)

.(4, 0)

Otherwise:
.(1, 2-bit condition code from SIOF (0 or 1))

.(1, unit status) (will have channel end and device end bits on)

.(1, channel status)

.(2, datacount)

.(datacount, data from last read or read sense operation)

If either device is working, c=2. If polling is already on, c=3. Otherwise, the polling flag is set on, a variable called seq is set to startseq, and a polling cycle is begun.

A polling cycle is:

A 0.2 second delay.

A start read.

A start write, sending the six bytes 0, 255, seq, 3, seq, 3.

When both devices are no longer working, if there was no error and the read data is the six bytes 0, 255, seq, 2, seq, 2, and the polling flag is still on, then seq is incremented mod 256 and another polling cycle is begun {else the endwait flag is set}.

c=0 and the polling flag is cleared. If the 0.2 second delay of a polling cycle is in progress, the polling cycle is aborted {and the endwait flag is set}.

This operation does what "abort poll" does, and in addition the endwait flag is set.

0 ok

1 rtod incorrect

2 device already working

3 operation already in progress

4 too much data

5 base not configured