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R b Kalin
MIT Lincoln Laboratory
February 24, 1971
Interrupt key
(RFC103-- Implementation of Interrupt Keys)
table of Contents
Problem Description 1
Solution 2
Note 3
The current protocol specification has a very serious logic error in the implementation of program interrupt functions. This document is for this
The problem is discussed and gives a relatively easy implementation solution.
Problem Description
Program interrupt key of most mutually shared systems (or Break Key ", help
Request button) has two functions. It hangs the current user process and converts the keyboard input stream to the background monitoring.
Process. An input that is not accepted before the interrupt request is saved in the buffer waiting to be pended. After
Enter is sent to the monitoring routine.
The current NCP protocol only implements a part of the above functions. It is used by INS and INR control information
The hang of the remote process is ready. But it does not provide a mechanism to notify the remote host to notify the data stream conversion time. INR and
The INS message is sent by the control chain. Due to the message on this chain and the user's keyboard input chain concurrently, receive the main
The machine cannot judge the synchronization source with relative arrival time. Lack of this information, remote NCP cannot judge input
The correspondence between characters and user processes and monitoring routines.
Some solutions to this problem in some systems are some of the code to map the interrupt signal to the character set, such as
ASCII code Control-C. But unfortunately, this method is not universal in the ARPA network. Some systems, such as
Multics, use all available ASCII codes as other purposes, no short leaves to this assignment. Even
A feature is now, as well as issues identified by the interrupt characters. If the buffer of the user chain is full,
The sender host cannot transmit messages containing the interrupt code. If the remote user process loops does not receive data,
Then, the buffer may never be idle, the message will never be incomed.
A limitative solution is to capture input in the server to provide a message scan process to capture input. Because of all
The input information is immediately destroyed, and the buffer can maintain the available state to enable the interrupt code. Unfortunately, this means
The time characteristics must be abandoned. Because after scanning, there may no space for them to be stored. Although this
It is not critical to the terminal interaction because the user can input only if the program requires input, but this
A defect makes the scanner unable to implement text-driven.
A solution
The solution of this problem is defined below the ASCII data stream.
1) Each character code of the character message should use an 8-bit digital domain.
2) For all defined ASCII character code, the left end of the 8-bit domain should be 0.
3) In the input sequence, an interrupt synchronization character should be placed at the appropriate point of the data stream (either to 8
Production code 200)
4) 8 The number of applications 201 to 377 are received by the host. They are reserved when they are necessary
Control information. Attempts to use it as additional character code will encounter from the intended character to be 7
Resistance of the PDP-10 system of the bit database. Note that the interrupt synchronous code should not be rejected, because they have
It is filtered by the system, never appears within the user input buffer. 5) Because there is a possibility that the user's information quota containing the interrupt synchronization character is allowed,
Existing INR / INS mechanism must be retained. When an interrupt synchronization character enters the text stream, it should
This sends an INS control information. When the external host receives the information, the additional process should
Stand up immediately and scan the relevant input stream. If possible, all to the interrupt synchronization character
The entry is called a buffer waiting for the suspend process. Once the sync character is found, the flow should be converted to
New activated monitoring process. If it is not possible to store the input of all user processes into the buffer,
Put it and send an error message to the user by the monitoring process. Any incident must be guaranteed
The input is destroyed and the message buffer is released to send unprocessed character messages.
6) When an interrupt synchronization character is received first matches INS, the user process should be suspended, NCP is
Further handle the waiting INS message.
7) Of course, the NCP function discussed above can be represented by a separate functional module, such as Telnet
process. If this is done, the NCP's message can be transparent.
Comment
Changes to the second level agreement here are not a general problem, but for the purpose of correcting key mistakes.
For a specific patch package currently with NCP design.
1) It only flows to the 7-bit code character. Do not allow words for EBCDIC, ASCII-8 or greater
The symbol is expanded. Although the author knows this concept means closing the connection, but there is no need to package
Processes containing character flows provide any explanation.
2) It requires the system to scan all the data from the interruptible connection. This means that when the connection is established
When it is, you must inform the receiving host scanning work has been completed. Implicit or explicit methods are available
use.
3) This technique is not processed on the situation where the character boundary is lost in a message body. At the same time, it allows it
The INS control message that does not contain the matching synchronization character, and vice versa.
4) Whether INS or text information sent to remote hosts to remote host characters may not be
can. Possible causes include user console errors, local host faults, network failures, control chains
Blocking, short quota, etc. In these cases, the remote process may enter the dead cycle.
Small changes to the current NCP protocol are not able to meet the only comprehensive all of the interrupt synchronization problem
The need for a difficult solution. If there is no more simple answer, their execution must be postponed to the next
The head large design revision work is completed.
[This RFC document is from Gert doering in April 1997]
[Component as a machine readable form to entered RFC online file]
RFC103 - Implementation of Interrupt Keys Interrupt button
1
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