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1 | @(#)README 3.6 %G% |
2 | ||
3 | /* | |
4 | * Copyright (c) 1983 Regents of the University of California, | |
5 | * All rights reserved. Redistribution permitted subject to | |
6 | * the terms of the Berkeley Software License Agreement. | |
7 | */ | |
84a5ea18 | 8 | |
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9 | Compilation notes: |
10 | ||
7c38ad4d | 11 | There is only one compiler option: |
84a5ea18 | 12 | |
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13 | mc68000 use 68000 byte ordering |
14 | It should already be defined in the preprocessor. | |
84a5ea18 | 15 | |
7c38ad4d | 16 | The file local.h contains locally tunable constants. |
84a5ea18 | 17 | |
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18 | The makefile should be updated with mkmf. The only library it needs |
19 | is termcap (and jobs for 4.1). | |
84a5ea18 | 20 | |
7c38ad4d | 21 | Window only runs on 4.2 machines. |
84a5ea18 | 22 | |
84a5ea18 | 23 | |
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24 | A few notes about the internals: |
25 | ||
26 | The window package. Windows are opened by calling wwopen(). | |
27 | Wwwrite() is the primitive for writing to windows. Wwputc(), wwputs(), | |
28 | and wwprintf() are also supported. Some of the outputs to windows are | |
29 | delayed. Wwupdate() updates the terminal to match the internal screen | |
30 | buffer. Wwspawn() spawns a child process on the other end of a window, | |
31 | with it's environment tailored to the window. Visible windows are | |
32 | doubly linked in the order of their overlap. Wwadd() inserts a window | |
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33 | into the list at a given place. Wwdelete() deletes it. Windows not in |
34 | the list are not visible, though wwwrite() still works. | |
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35 | |
36 | Most functions return -1 on error. Wwopen() returns the null | |
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37 | pointer. An error number is saved in wwerrno. Wwerror() returns an |
38 | error string based on wwerrno suitable for printing. | |
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39 | |
40 | The terminal drivers perform all output to the physical terminal, | |
41 | including special functions like character and line insertion and | |
42 | deletion. The window package keeps a list of known terminals. At | |
43 | initialization time, the terminal type is matched against the list to | |
44 | find the right terminal driver to use. The last driver, the generic | |
45 | driver, matches all terminals and uses the termcap database. The | |
46 | interface between the window package the terminal driver is the `tt' | |
47 | structure. It contains pointers to functions to perform special | |
48 | functions and terminal output, as well as flags about the | |
49 | characteristics of the terminal. | |
50 | ||
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51 | The IO system is semi-synchronous. Terminal input is signal |
52 | driven, and everything else is done synchronously with a single | |
53 | select(). | |
533eb3f8 | 54 | |
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55 | Normally, in both conversation mode and command mode, window |
56 | sleeps in a select() in wwiomux() waiting for data from the | |
57 | pseudo-terminals. At the same time, terminal input causes SIGIO which | |
58 | is caught by wwrint(). The select() returns when at least one of the | |
59 | pseudo-terminals becomes ready for reading. | |
533eb3f8 | 60 | |
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61 | Wwrint() is the interrupt handler for tty input. It reads input |
62 | into a linear buffer accessed through four pointers: | |
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63 | |
64 | +-------+--------------+----------------+ | |
65 | | empty | data | empty | | |
66 | +-------+--------------+----------------+ | |
67 | ^ ^ ^ ^ | |
68 | | | | | | |
69 | wwib wwibp wwibq wwibe | |
70 | ||
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71 | Wwrint() appends characters at the end and increments wwibq (*wwibq++ = |
72 | c), and characters are taken from the buffer at wwibp using the | |
73 | wwgetc() and wwpeekc() macros. As is the convention in C, wwibq and | |
74 | wwibe point to one position beyond the end. In addition, wwrint() will | |
75 | do a longjmp(wwjmpbuf) if wwsetjmp is true. This is used by wwiomux() | |
76 | to interrupt the select() which would otherwise resume after the | |
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77 | interrupt. The macro wwinterrupt() returns true if the input buffer is |
78 | non-empty. Wwupdate(), wwwrite(), and wwiomux() check this condition | |
79 | and will return at the first convenient opportunity when it becomes | |
80 | true. In the case of wwwrite(), the flag ww_nointr in the window | |
81 | structure overrides this. This feature allows the user to interrupt | |
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82 | lengthy outputs safely. The structure of the input buffer is designed |
83 | to avoid race conditions without blocking interrupts. | |
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84 | |
85 | Wwiomux() copies pseudo-terminal outputs into their corresponding | |
86 | windows. Without anything to do, it blocks in a select(), waiting for | |
87 | read ready on pseudo-terminals. Reads are done into per-window buffers | |
88 | in the window structures. When there is at least one buffer non-empty, | |
89 | wwiomux() finds the top most of these windows and writes it using | |
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90 | wwwrite(). Then the process is repeated. A non-blocking select() is |
91 | done after a wwwrite() to pick up any output that may have come in | |
92 | during the write, which may take a long time. Specifically, we use | |
93 | this to stop output or flush buffer when a pseudo-terminal tells us to | |
94 | (we use pty packet mode). The select() blocks only when all of the | |
95 | windows' buffers are empty. A wwupdate() is done prior to this, which | |
96 | is the only time the screen is guaranteed to be completely up to date. | |
97 | Wwiomux() loops until wwinterrupt() becomes true. | |
98 | ||
99 | The top level routine for all this is mloop(). In conversation | |
100 | mode, it simply calls wwiomux(), which only returns when input is | |
101 | available. The input buffer is then written to the pseudo-terminal of | |
102 | the current window. If the escape character is found in the input, | |
103 | command mode is entered. Otherwise, the process is repeated. In | |
104 | command mode, control is transferred to docmd() which returns only when | |
105 | conversation mode is reentered. Docmd() and other command processing | |
106 | routines typically wait for input in a loop: | |
107 | ||
108 | while (wwpeekc() < 0) | |
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109 | wwiomux(); |
110 | ||
115fa6f8 | 111 | When the loop terminates, wwgetc() is used to read the input buffer. |
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112 | |
113 | Output to the physical terminal is handled by the lowest level | |
114 | routines of the window package, in the files ttoutput.c and tt.h. The | |
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115 | standard IO package is not used, to get better control over buffering |
116 | and to use non-blocking reads in wwrint(). The buffer size is set to | |
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117 | approximately one second of output time, based on the baudrate. |
118 | ||
119 | The result of all this complexity is faster response time, | |
120 | especially in output stopping and flushing. Wwwrite() checks | |
121 | wwinterrupt() after every line. It also calls wwupdate() for each line | |
122 | it writes. The output buffer is limited to one second of output time. | |
123 | Thus, there is usually only a delay of one to two lines plus one second | |
124 | after a ^C or ^S. Also, commands that produce lengthy output can be | |
125 | aborted without actually showing all of it on the terminal. (Try the | |
115fa6f8 | 126 | '?' command followed by escape immediately.) |