Group Coded Recording (GCR) 6250 BPI Magnetic Tape DLP

The GCR Mag Tape DLP supports various magnetic tape Control units (TCU) and transport units (MTU).

Style Description
B9494-21/22/23/24 GCR TCU
B9495-24 MTU 200IPS
B9495-32/33 5G PE/GCR MTU
B9495-32M PE/GCR TCU
B9495-32 5G PE/GCR MTU
B9495-33M PE/GCR TCU
B9495-33 5G PE/GCR MTU

I/O Descriptors

Operation SYS OP MLI OP S L1 L2 L3 Addresses Used?
READ 40 8
Forward * 2 U 0 A-B Yes
Backward 41 * 3 U 0 A-B Yes
Extended Status * D U 0 A-B Yes
Unit Status * E U 0 A-B Yes
Buffer * F U 0 A-B
WRITE 42 4
Data * 0 U d A-B Yes
Buffer * E U 0 A-B
TEST 44 2
Unit * 0 U 0 Yes
Wait for Ready * 1 U 0
Wait for Not Ready * 2 U 0
Rewind * 4 U 0 Yes
Rewind/Unload * 5 U 0 Yes
Cancel * 8 U 0
ID * C 0 0 ?
Write Tape Mark * D U d Yes
TEST 54 2
Space Forward * 6 U x A-B*, C Yes
Space Backward * 7 U x A-B*, C Yes
Erase * E U x A-B*, C Yes
Data Security Erase * F U d A-B*, C ?

U designates unit number.

The C Address designates space count for Space operations only.

d designates the density bit. Bit-1 set to 1 indicates operation to be performed in GCR mode, Bit-1 set to 0 indicates operation to be performed in PE mode.

x designates density and space count. Bit-1 is density (see d). Bit-2 set to 1 indicates space count is in decimal, set to 0 indicates space count is binary.

* These Test commands do not transfer data, however A-B addresses are required to have a C address field that contains the space count information. Typically the buffers will be set to small addresses such as 0/4, or will simply be the same buffer addresses as used for some preceeding Write or Read operation.

Command Formats

4X series system opcodes have two addresses. The A and B addresses are the start and end of the memory transfer buffer. Some operations do not transfer any data other than the command and result descriptors. The A and B addresses are typically set to 0 in this case.

5X series system opcodes have three addresses. The A and B addresses are the start and end of the memory transfer buffer. The C address contains 8 digits of extra parameters for the command. In this case the space/skip count is in the C address.

Test/Wait Ready - Test/Wait Not Ready

The Test/Wait operators are not used on tape devices, even though they are functional. The design of the V Series I/O subsystem will mark a channel as busy one a Test/Wait operator is issued to some drive on the channel. The channel will remain busy until the Test/Wait operation completes. While the channel is busy no operations can be issued to other tape drives connected to the channel. To allow operations to be issued to all drives on the channel, periodic Test Unit operations are issued to idle tape drives to detect a status change, rather than issuing Test/Wait operators.

With advent of the IOCB mechanism in MCPVS 3.0 and successors, the I/O subsystem would allow multiple I/O operations to be initiated to a channel, but the operating system was never enhanced to use the TEST/Wait I/O descriptors. The TEST/Wait operations are supported by the simulator GCR dlp.

Space

The first 4 digits of the C Address contains the space count in either binary or decimal encoding. The space count is the number of tape blocks to space, forward or reverse. The MCP Space/Skip BCT allows a space count of +-9999 blocks.

Older tape controls/drives only had a 2-digit decimal space count, and the MCP would loop multiple Space operations until the space count was reached. This method was retained for the GCR Tape DLP as Space operations are very slow, and breaking the spacing up into multiple operations allowed the channel to be used to talk to other tape drives more often.

The Space operation will space the number of blocks requested, unless a tapemark or BOT/EOT is sensed. If the Space operation stops for one of these reasons the R/D will show the reason. A Space operation may also stop for Timeout. This can occur when attempting to space on unrecorded tape. SOme tape controls will attempt to reposition to just after the last valid block in this case. Others simply stop wherever they are. Tape position cannot be relied on when a Timeout result occurs.

The space count will be in decimal unless a particular tape control only supports binary encoding.

Erase

The Erase operator uses a flag or count in some field inthe C address. «I no longer remember what this flag did»

Read Unit Status

The buffer is 8 digits in length.

A B C D E F G H
8 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN DENSITY
0 = 1600
1 = 6250
UNKNOWN UNKNOWN
4 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN
2 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN
1 UNKNOWN UNKNOWN UNKNOWN UNKNOWN SHARED
UNIT
UNKNOWN UNKNOWN UNKNOWN

The SHARED bit is set if the magnetic tape controller is shared by multiple hosts. In this case, MCPIV, MCPIX and MCP/VS will automatically mark the drive as SAVED as if it had been declared with the SHARED attribute at coldstart and halt/load time. The operator must explicitly ready RY the tape unit prior to use.

The density bit informs the operating system the density of the currently mounted media.

The above information was determined empirically.

GCR Magnetic Tape DLP Result Descriptor Word 1

A B C D
8 TCU
NOT READY
EARLY
TERMINATION
INCORRECT
STATE
UNIT
NOT
READY
4 DESCRIPTOR
ERROR
READ
EXTENDED
STATUS
DIS-
CONTINUED/
CANCELLED
ZERO
2 VERTICAL
PARITY ERROR
(MLI)
TCU
TIMEOUT
DATA
ERROR
TRANS-
MISSION
ERROR
1 LONGITUDINAL
PARITY
ERROR
(MLI)
INVALID
INFORMATION
HOST
ACCESS
ERROR
EXCEPTION

The GCR Tape Subsystem consisted of three units: the GCR Tape DLP, the Tape Control Unit (TCU), and one or more Magnetic Tape Units (MTUs). The first word of the DLP R/D was provided by conditions detected by the DLP.

TCU Not Ready: The TCU is offline.

Descriptor Error, and the MLI parity errors are standard for all DLPs.

Early Termination: A command ended before it was expected?

Read Extended Status: There is information in words 2-3 of the DLP result descriptor.

TCU Timeout: The TCU failed to complete a command. This typically indicated a microcode fault in the TCU.

Invalid Information: ?

Incorrect State: The TCU didn't like something, but I no longer recall what.

Discontinued/Cancelled: The command was discontinued or canceled. Typically occurs on a Test/Wait.

Data Error: Incorrect data to or from(?) the TCU to the DLP.

Host Access Error: The tape is moving faster than the host memory access bandwidth can support.

Unit Not Ready: The addressed MTU is not ready or offline.

Transmission Error: ?

Exception: Set if any other bits are set in words 1 or 2 of the R/D.

GCR Magnetic Tape DLP Result Descriptor Word 2

A B C D
8 INVALID
OP
RECEIVED
WRITE
LOCKOUT
BOT
(Beginning of Tape)
UNIT
CHECK
4 MTU
NOT READY
TAPE
MARK
EOT
(End of Tape)
DATA NOT
TRANS-
FERRED
2 TCU
TRANS-
MISSION
ERROR
DATA
SECURITY
ERASE/
REWIND NOT
INITIATED
REWINDING ERROR
CORRECTION
1 DATA
CHECK
(PARITY
ERROR)
DEVICE
TIMEOUT
MTU
BUSY
SHORT
BLOCK

The GCR Tape Subsystem consisted of three units: the GCR Tape DLP, the Tape Control Unit (TCU), and one or more Magnetic Tape Units (MTUs). The first word of the DLP R/D was provided by conditions detected by the DLP. The second word was primarily passed through from the TCU.

Invalid Op Received: The TCU received an invalid operation code from the DLP. This most likely indicated a parity error on the cable from the DLP to the TCU.

MTU Not Ready: The addressed tape drive is not ready.

TCU Transmission Error: A parity error on the cable from the TCU to the DLP, or from the TCU to the MTU.

Erase/Rewind Not Initialted: A device condition in the MTU prevented the requested Erase or Rewind from occurring.

Timeout: A command could not complete in a reasonable time or reasonable length of tape. This would most commonly occur when attempting a Read or Space operation on blank tape, or tape that was not recorded in GCR or PE format.

BOT: A backwards operation (Rewind or Space or Read Backwards) has reached the start mark on the tape. Also occurs when a tape is initially mounted before the MCP reads the beginning label.

EOT: A forwards operation (Read, Write, Space, or Erase) has reached the end mark on the tape. EOT will terminate a forward Space or Erase Multiple operation, but does not terminate a Read or Write. There is sufficient room on the tape after the EOT mark to flush the current file buffers and write an ending label. (If the user does not have an excessive number of buffers or buffers of excessive size.)

Rewinding: Typically returned on a Test Unit operation, it indicates that a Rewind has been issued (possibly locally at the tape drive) and the tape has not reached BOT.

MTU Busy: The tape unit is busy performing an operation. In most cases the DLP does not complete an operation while the tape is still in motion, so this R/D bit will generally not be reported. It would most likely show up if the TCU is connected to multiple tape controls and the MTU was interrogated through an alternate path. This most commonly occurs on shared tape systems, as the MCP that issued a command to a unit through one path knows better than to interrogate it through another path during the command.

Unit Check: The MTU has discovered a serious fault of some kind or other. It is necessary to do a Read Extended Status to detetermine the actual fault, and to clear the Unit CHeck indication if the fault is transient. (If I remember correctly!)

Data Not Transferred: An error occurred before any data was transferred to or from the tape in the current Read or Write request. This can be used to determine the severity of other error conditions. (However I believe the MCP ignores this bit.)

Error Correction: GCR tape has an ECC code that permits some tape errors to be corrected. This bit will be set if a block has been corrected. The MCP logs but otherwise ignores this bit.

Short Block: The physical tape block was not as long as the declared buffer between the A and B addresses. Normally this should only occur on a Read operation. This may be a fatal error or be ignored, depending on a setting inthe user's FIB.

GCR Magnetic Tape DLP TEST/ID Result Descriptor Word 2

A B C D
8 0 1 X X
4 0 1 X X
2 0 0 X X
1 0 1 X X

X - field installed jumpers (not used for medium systems)

Each GCR Tape DLP can be jumpered with a specific code. This code is not used by the V Series MCP and is typically left unjumpered, returning a value of 00. (This feature was implemeted for the Large Systems MCP.)

Fujitsu BT3200 Tape Drive

Model Transfer Rate Density Speed
(IPS)
BT3240 470 KB 1600/6250 75
BT3260 780 KB 1600/6250 125
BT3280 1250 KB 1600/6250 200

BT3200 Tape Drive

dlps/gcr_tape.txt · Last modified: 2013/01/23 16:12 by scott
 
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