semi合集-English.pdf - 第1228页

SEMI E5-1104 © SEMI 1982, 2004 170 10.17.2. 9.3 The size of the secondary message may be less because of l imited reso urces in the sendi ng system. 10.17.2. 9.4 For data sets with Discrete records, the for- mat of each …

SEMI E5-1104 © SEMI 1982, 2004 169

2. The beginning of the data set has Checkpoint value

with all bits reset.

3. A Checkpoint with all bits set is illegal.

4. A Checkpoint supplied by the sending system

which does not have all bits set is usable in an

OPEN transaction to restart a data transfer without

any lost data or duplicated data.

10.17.2.5.2 The receiving system defines the initial

Checkpoint in the primary message of the OPEN trans-

action. The sending system returns the next Checkpoint

in the response to each READ.

10.17.2.6 Read Length — The Read Length must be

supplied by the receiving system with each READ

transaction. It specifies the maximum number of data

bytes which that system is prepared to process at one

time. The sending system may supply less if it has lim-

ited resources. The sending system may supply more if

ReadLength is zero, or is smaller than RecordLength.

10.17.2.7 Reading a Data Set — The basic data

transfer is initiated with the OPEN transaction and

completed with the CLOSE transaction. Information is

sent from the sending to the receiving systems by a

series of READ transactions.

10.17.2.8 OPEN Transaction — The receiving system

sends a primary message containing the DataSet Name

of the desired data set, the Handle to be used, and the

Checkpoint of the initial READ transaction. The

response from the sending system is a secondary mes-

sage with a return code and the RecordType and

RecordLength of the data set. If the return code is one

of the error codes, then no data set was opened and the

values of RecordType and RecordLength are undefined.

If the RecordType is Stream, then the value of

RecordLength is undefined. Notice that the undefined

items will still appear in the secondary message.

10.17.2.8.1 The return code in the secondary message

is one of the following:

OK.

ERROR: Unknown Data Set ID.

ERROR: Try later (i.e., the data set is in use).

ERROR: Too many open data sets.

ERROR: Data set open too many times.

ERROR: Handle in use.

ERROR: Pending Transaction.

10.17.2.9 The READ Transaction — The receiving

system sends a primary message which contains the

Handle, and the ReadLength. The sending system

responds with a secondary message which has a return

code, the next Checkpoint, and zero or more items with

data. At least one data item must be supplied unless

there is an error. The return codes are:

OK.

ERROR: End of Data.

ERROR: No open Data Set (i.e., incorrect Handle).

ERROR: Cannot continue (i.e., a disk read error on the

sending system).

ERROR: Pending Transaction.

10.17.2.9.1 Any READ transaction which follows a

READ which returned an error, except “Pending

Transaction,” will generate the same error. The value

of Checkpoint must be illegal (i.e., all bits must be set)

when the “End of Data,” “No open Data Set,” or

“Pending Transaction” error is returned. The value of

Checkpoint error must be a value from which recovery

may be attempted without duplicating data when the

“Cannot continue” error is returned. Recovery may be

attempted by issuing a CLOSE, followed by an OPEN

with the last value of Checkpoint, and then another

READ.

10.17.2.9.2 Each secondary message for the READ

transaction must contain a whole number of Discrete

records. A record may be sent as an ASCII or a binary

item. Stream data sets are broken into pieces by the

READ transaction without regard to internal structure.

Each piece would be sent as a single binary item. The

number of items which contain data depends on the

RecordType, Record Length, and Read Length. The

algorithm is designed so that the maximum length of

the secondary message is deterministic. It gives the

receiving system the ability to control the amount of

resources (such as SECS-I buffers) which it must allo-

cate. The sending system may send less data than the

maximum if it has limited resources. The performance

(i.e., the packing of records into a message of some

maximum size) should be very good for the case where

records are all nearly the maximum length. This is

assumed to be the usual case. The efficiency in patho-

logical cases (e.g., many short records) will not be

good, but the algorithm is robust enough to accommo-

date this without exceeding the maximum message size.

NOTE 13: If the RecordType is Stream, then there is exactly

one item with a binary format whose length is not more than

ReadLength. If the RecordType is Discrete, then the

maximum number of items, MaxItems, is calculated by the

formula:



























thRecordLeng

ReadLength

int,1maxMaxItems

SEMI E5-1104 © SEMI 1982, 2004 170

10.17.2.9.3 The size of the secondary message may be

less because of limited resources in the sending system.

10.17.2.9.4 For data sets with Discrete records, the for-

mat of each item is either ASCII (format 20) or binary

(format 10). There is no requirement that all records be

in the same format, but mixed record formats are not

encouraged. Items with ASCII format should have only

data characters. Characters which the sending system

uses for control information (e.g., newline for a record

terminator) should not appear. If an application finds it

necessary to include these characters, then format 10, or

Stream should be used.

10.17.2.10 CLOSE Transaction — This transaction ter-

minates a data transfer and frees the Handle for future

use. The primary message is sent by the receiving sys-

tem and contains only the Handle. The sending system

responds with a secondary message which has a return

code.

10.17.2.10.1 The return code is one of the following:

OK.

ERROR: No open Data Set (i.e., incorrect Handle).

ERROR: Pending Transaction.

10.17.2.11 Sending a Data Set — Writing a data set is

performed by requesting that the receiving system read

it. The sending system initiates the SEND transaction

to request that a data set be read. The receiving system

is expected to perform the OPEN, READ, and CLOSE

transactions to transfer the data set if it accepts the

request. The time between the secondary message of

the SEND and the primary message of the OPEN

depends on the application.

10.17.2.12 The SEND Transaction — The primary

message sent from the sending system to the receiving

system contains the Data Set Name.

10.17.2.12.1 The secondary message contains the Data

Set Name and a return code which is one of the follow-

ing:

OK.

ERROR: Unknown Data Set Name.

ERROR: Try later (i.e., the system is busy).

10.17.2.13 Error Recovery — The receiving system

may crash while a data set is open but no READ trans-

action is pending. The sending system will not be able

to tell that this has happened because there is no time-

out value defined between READ transactions. When

the receiving system is restarted it may have forgotten

which data sets were open. States in the two systems

are now inconsistent.

10.17.2.14 RESET Transaction — The RESET transac-

tion offers a way to resynchronize the two systems.

When one system issues the primary message of the

RESET transaction, it is informing the other system that

any data sets which may have been open are to be

closed. This applies to all data sets open between both

systems. It is not necessary to issue CLOSE transac-

tions for each individual data set because the RESET

transaction is a global close.

10.17.2.15 Any equipment which uses Stream 13 must

issue the RESET transaction as part of its initialization

or bootstrap procedure. A host system must issue a

RESET to equipment which uses Stream 13 during the

initialization for that equipment.

10.17.2.16 SECS-II Protocol Definition —

Figure 11

shows the state diagram for the sending system while a

data set is being transferred. Each circle shows a possi-

ble state of the sending system. The names of these

states are for reference only. They are not meant to

suggest an implementation. The arrows show transi-

tions due to SECS-II messages received or sent by the

sending system.

10.17.2.16.1 In the initial state (Idle) handle X is not

open. The states marked with an asterisk are those in

which a transaction is outstanding. If the sending sys-

tem receives any primary message from the receiving

system with handle X during the time it is in these

states, then the secondary message for that transaction

will contain the “Pending Transaction” error code, but

the original transaction for handle X will not be

affected. Some states, especially the error states, may

take zero time in some implementations. In these cases,

the “Pending Transaction” error code would not be

returned from those states.

10.17.3 Formatted Data Sets — Formatted data sets

are data sets transferred in a standard format. Stream

13 provides a method for transferring data sets in a

table format. A table has both attributes and content.

The attributes of the table provide information about the

data set as a whole, such as the date and time that it was

last modified, its size, etc. The content of the table

consists of column headers and rows. A row is an

ordered list of table elements. A column refers to all

table elements at a specific position within all rows,

where each column is identified by a corresponding text

string as a column header. The table elements in the 1st

column position are used as an identifier for the row.

Stream,Function Name (Mnemonic) Direction

S13,F0 Abort Transaction (S13F0) S,H<->E

Description

Same form as S1,F0.

Structure

Exception

Stream,Function Name (Mnemonic) Direction

S13,F1 Send Data Set Send (DSSS) S,H<->E,reply

Description

Sent by the sending system to request that the other system read a dataset.

Structure

L,1

1. <DSNAME>

Exception

None

Stream,Function Name (Mnemonic) Direction

S13,F2 Send Data Set Acknowledge (DSSA) S,H<->E

Description

Sent by the receiving system in response to Send Data Set Send.

1. <DSNAME>

2. <ACKC13>

Structure

Exception

The possible ACKC13 codes for this message are:

0 = O.K.

1 = ERROR:Try later.

2 = ERROR:Unknown Data Set Name.

Stream,Function Name (Mnemonic) Direction

S13,F3 Open Data Set Request (DSOR) S,H<->E,reply

Description

Sent by the receiving system to open a data set for reading.

Structure

L,3

1. <HANDLE>

2. <DSNAME>

3. <CKPNT>

Exception

None