Host Control-2 (HC-2) DLP

The Intersystem connect (ISC) is a high-speed, data link processor-based interface for connecting Unisys computers in a local-area network. Interfaces are provided through BNA, BPL and COBOL.

Using ISC, any combination of B 2900, B 3800, B 3900, B 4800, B 4900, B 5900, B 6900, B 7900, V Series, A Series and CP9500 hosts can be configured in a local-area network. The center of the network is the B9320-4 (4 port) or B9320-5 (16-port) HUB, which can support a network from two to 16 hosts. The connection between the hub and each host is made through an HC-2 data link processor (DLP) which resides in a DLP base within the host.

Hub Characteristics

The hub is a polling and message routing device which connects from two to 16 host controls (HC's).

The hub continuously polls the HCs connected to it, awaiting Write requests. When a Write request is detected, the hub coordinates the connection and data transfer between the sending HC and the receiving HC. Only a single data transfer can be in progress through the hub at any time. The polling scheme grants equal priority to all of the HCs connected to the hub; after one HC's request has been serviced, the hub polls the next HC.

The Hub Index

The hub contains connectors for 16 host control; the positions of the connectors are numbered from 0 to 15. The position into which an HC is cabled determines its hub index. The hub index is a 1-relative number from 1 to 16, which i used by the software and the hub as a key to direct messages to particular HCs. Position 0 is hub index 1; position 8 is index 9 and so forth.

The Hub Identification Number

The hub contains a set of 16 toggle switches. The setting of these switches determines a 16-bit hub identification number. The hub identification number is stored internally in the hub and can be interrogated programmatically to determine the identity of the hub to whic ha program, through its host's HC, is connected.

Host Control Characteristics

The host control (HC) is the I/O interface bewteen the hub and a host. The host control used for V-Series hosts as well as all A-Series and Medium and Large systems, is the HC-2 data link processor (DLP).

The HC-2 is a bi-directional device (read and write) occupying a single position (3 cards) in the host's DLP base, and one slot in the hub. The HC-2 is a half-duplex device; that is data is only transferred one direction at a time. However you can configure a system with two uni-directional HC-2s, one to read and one to write. This can reduce I/O and processor overhead and can improve total I/O throughput.

Single and Dual HC-2 Configurations

A configuration containing a single HC-2, performing both reads and writes is typically slower than a configuration containing two HC-2 devices, one dedicated to reads and one dedicated to writes. This is due to the fact that the MCP maintains a default read operation at all times.

In a single HC-2 configuration, every non-read operation requires two I/O operations; one to cancel the default read and one to perform the requested function. In a dual HC-2 configuration the primary HC-2 is dedicated to reads and the secondary HC-2 is dedicated to writes; therefore any operation can be accomplished immediately. In other words, a dual HC-2 system runs as full-duplex, while a single HC-2 configuration runs as half-duplex.

HC-2 Strapping Requirements

For host controls used on Medium systems or V-Series, a connection referred to as the non-standard strap must be installed. The non-standard strap enables the output of the host control to be understood by the V-series hardware (certain lines are disabled) and causes the data transfer size to be interpreted as a decimal number.

The maximum data transfer size of a single I/O through an HC on a B 2900, B 3900, B 4900 or V-Series host is 9999 bytes.

ISC-HC Data Transfer Rate

The maximum data transfer rate of the host control is one million bytes (1000 KB) per second. The transfer rate actually achieved will be less than this amount because individual data transfer sizes are relatively small and there is some overhead associated with issuing each request.

Access Mask Register

Each Host Control contains an access mask register (AMR) which indicates the power-on status of the HC, specifies the current file status of the HC and which can contain other programmer specified information.

The AMR consists of three 16-bit words for a total length of 48 bits. The format of an access mask register is:

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Word 1 HC
Power
Unused Open
Mode
Word 2 User Defined
Word 3 BNA Host ID
or User Defined

Two operations are available to operate on AMR(s). Write AMR writes a value into an HCs AMR, while Read AMR returns the contents of the AMRs of all HCs on the hub.

The HC Power bit is set when power is applied to the HC and is reset when power is not applied. Interrogation of this bit for any hub index position enables an ISC program to determine which positions have active HC's.

The Open Mode bits indicate the current I/O mode of the HC and can be used to determine the valid I/O requests (Read, Write, both or neither) which can be made to the this HC from another HC. The values of this field and their meanings are:

Value Meaning
00 Closed
01 Read-Only (may only be written to)
10 Write-Only (may only be read from)
11 Read/Write (can be written to or read from)

MCP Requirements

To declare an ISC Host Control DLP to the MCP, the DLP record is used:

DLP 35 ISC

To declare an ISC device, the UNIT record is used:

UNIT 35/0 ISCA ISC

This shows a dual HC configuration:

DLP 26 ISC
DLP 27 ISC
EXCHANGE 26 + 27
UNIT 26/0 ISCB ISC RETRY 12

Simulator Implementation Notes

An instance of the DLP is specified to the simulator with the channel command as follows:

vsim> channel 55 isc

The following commands may be used to configure the HC-2 DLP:

control CC/0 hub **hostname** **port** **hub-index**
control CC/0 status

The hub command is used to establish a connection to the ISC HUB process by specifying the hostname (or IP address) and TCP port number to use to connect to the hub. The Hub-index will be transmitted to the hub to specify which hub-index on the HUB this DLP is attached to. Note there is no checking for duplicate hub-index assignments by the hub.

vsim> control 55/0 hub localhost 3555 2
vsim> control 55/0 status
0055/00  Connection pending to hubindex 2 at localhost:3555
vsim> !utilities/ischub/ischub -i 1331 -p 3555
0055/00  Connected to the HUB at localhost:3555
vsim> control 55/0 status
0055/00  is connected to localhost:3555 on hubindex 2
Access Mask Register: [8000/0000/0000]
Pend WR? N      Pend WNR? N   Default Read? N
Pend Write? N   Pend WAMR? N  Pend RAMR? N
Next Packet Sequence: 1
Transmit Frame Counts:
   Info:  0   RR: 0   LR: 0  Disc: 0  Test: 0
Recieve Frame Counts:
   Info:  0   RR: 0   LR: 0  Disc: 0  Test: 0
Unknown Transmit Frames: 0
Unknown Recieve Frames: 0

I/O Descriptors

Operation SYS OP MLI OP S L1 L2 L3 Addresses Used?
READ 50 8
AMR * 1 0 0 A-B Yes
Wait for Request * 2 0 0 A-B Yes
Hub Index * 3 0 0 A-B Yes
Unit Status * E 0 0 A-B Yes
Buffer * F 0 0 A-B
WRITE 52 4
Data * 0 U V A-B,C Yes
AMR * 1 0 0 A-B Yes
Through Hub * E U 0 A-B Yes
Buffer * F U 0 A-B
TEST 54 2
Unit * 0 U 0 Yes
Wait for Hub Avail * 1 0 0 A-B
Wait for Not Hub Avail * 2 0 0 A-B
Cancel * 8 0 0
Discontinue * A 0 0
ID * C 0 0 ?

U designates hub index.

The C Address of the Write Data operation indicates the length of the operation.

V Purpose
0 Write Immediate
1 Write with 30 second timeout
2 Write Immediate with Read Pending
3 Write with 30 secodn timeout, with read pending

HC-2 DLP Result Descriptor Word 1

A B C D
8 HUB
NOT READY
EARLY
TERMINATION
INCORRECT
STATE
ZERO
4 DESCRIPTOR
ERROR
ZERO DIS-
CONTINUED/
CANCELLED
ZERO
2 VERTICAL
PARITY ERROR
(MLI)
ZERO DATA
ERROR
DLP MAL-
FUNCTION
1 LONGITUDINAL
PARITY
ERROR
(MLI)
INVALID
INFORMATION
HOST
ACCESS
ERROR
EXCEPTION

Hub Not Ready: The Hub is offline.

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

Early Termination: A command ended before it was expected?

Invalid Information: ?

Incorrect State: The Hub didn't like something?

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

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

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

Transmission Error: ?

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

HC-2 DLP Result Descriptor Word 2

A B C D
8 WRITE
DENIED
HUB
UPW
ERRROR
PARTNER
EXCEPTION
PARTNER
SYSTEM
HUB INDEX
4 CONTROL
TRANSFER
TIMEOUT
HUB
LPW
ERROR
AMR
CLEARED
PARTNER
SYSTEM
HUB INDEX
2 DATA
TRANSFER
TIMEOUT
MLI
LENGTH
ERROR
READ
SYSTEM UN-
AVAILABLE
PARTNER
SYSTEM
HUB INDEX
1 LENGTH
ERROR
AMR
ERROR
READ
PENDING
PARTNER
SYSTEM
HUB INDEX

HC-2 DLP TEST/ID Result Descriptor Word 2

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

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

Each HC-2 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.)

dlps/host_control_2.txt · Last modified: 2012/02/04 15:10 by scott
 
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