-
Notifications
You must be signed in to change notification settings - Fork 0
/
rk11-3.html
218 lines (176 loc) · 9.12 KB
/
rk11-3.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>fritzm.github.io - PDP-11/45: RK11 III</title>
<meta name="description" content="">
<meta name="author" content="Fritz Mueller">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- Le HTML5 shim, for IE6-8 support of HTML elements -->
<!--[if lt IE 9]>
<script src="https://fritzm.github.io/theme/html5.js"></script>
<![endif]-->
<!-- Le styles -->
<link href="https://fritzm.github.io/theme/bootstrap.min.css" rel="stylesheet">
<link href="https://fritzm.github.io/theme/bootstrap.min.responsive.css" rel="stylesheet">
<link href="https://fritzm.github.io/theme/local.css" rel="stylesheet">
<link href="https://fritzm.github.io/theme/pygments.css" rel="stylesheet">
<!-- Photoswipe -->
<link rel="stylesheet" href="https://fritzm.github.io/theme/photoswipe.css">
<link rel="stylesheet" href="https://fritzm.github.io/theme/default-skin/default-skin.css">
<script src="https://fritzm.github.io/theme/photoswipe.min.js"></script>
<script src="https://fritzm.github.io/theme/photoswipe-ui-default.min.js"></script>
<script src="https://fritzm.github.io/galleries.js"></script>
<script type="text/javascript">
var pswipe = function(gname, index) {
var pswpElement = document.querySelectorAll('.pswp')[0];
var items = galleries[gname];
var options = { index: index };
var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, options);
gallery.init();
};
</script>
<!-- So Firefox can bookmark->"abo this site" -->
<link href="https://fritzm.github.io/feeds/all.rss.xml" rel="alternate" title="fritzm.github.io" type="application/rss+xml">
</head>
<body>
<div class="navbar">
<div class="navbar-inner">
<div class="container">
<a class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</a>
<a class="brand" href="https://fritzm.github.io">fritzm.github.io</a>
<div class="nav-collapse">
<ul class="nav">
</ul>
</div>
</div>
</div>
</div>
<div class="container">
<div class="content">
<div class="row">
<div class="span9">
<div class='article'>
<div class="content-title">
<h1>PDP-11/45: RK11 III</h1>
Sun 26 February 2017
by <a class="url fn" href="https://fritzm.github.io/author/fritz-mueller.html">Fritz Mueller</a>
</div>
<div><p>Okay, the M9202 bus jumper arrived, and like the 2-foot BC11 cable, the occasional timeouts go away when this
is installed. Hantek digital scope also arrived, so I decided to throw it on the backplane for a closer
look at the SSYN and timeout signals. The results were pretty interesting. Here's a capture of an RKCS
access triggering a timeout glitch with the M902. The yellow trace is BUS A SSYN L (taken from C12J1 on the
11/45 backplane), and the blue trace is UBCB TIMEOUT (1) H (taken from D12U1):</p>
<p><img src='/images/pdp11/rkcs-timeout.jpg'/></p>
<p>What's interesting is that with the M9202 in place, the SSYN waveform shape on RCKS accesses is <strong>not</strong>
significantly different -- and the timeout glitch still ocurrs from time to time, but at a reduced amplitude:</p>
<p><img src='/images/pdp11/rkcs-glitch.jpg'/></p>
<p>If the problem had been one solely of lumped loads on the bus, I would have expected the fix to manifest
as a waveform difference, and for the glitches to have disappeared. These observations steered me back
toward my original (less plausible?) supposition -- the the 74123 one-shot in the Unibus timeout logic in the
CPU was flaky, and particularly sensitive for some reason to SSYN pulses of 568ns. Adding some extra bus
length via a BC11 or the M9202 moves the timing by a nano or two off the troublesome period, and reduces the
magnitude of the glitches.</p>
<p>So I went ahead and clipped out the suspect 74123, and put in a socket and a fresh part. Bingo! Timeout
glitching was eliminated entirely. Here's a trace after the 74123 was replaced. This trace looks different
because with the timeout glitch fixed, I could no longer use it to trigger the scope -- instead I had to
trigger on the trailing edge of SSYN, so we see both RKCS and non-RKCS bus cycles. In any case, the timeout
glitching is now gone:</p>
<p><img src='/images/pdp11/rkcs-fixed.jpg'/></p>
<p>So that's a nice result -- I think the new scope is going to be pretty useful. The rather extreme sawtooth
on the falling edge of SSYN on RKCS accesses still looks pretty bad to me, even though it is no longer
triggering timeouts. I might try swapping out the M105 address decoder on the RK11, which generates this
signal, and see if the integrity here is improved. All for now!</p></div>
<hr>
</div>
</div>
<div class="span3">
<div class="well" style="padding: 8px 0; background-color: #FBFBFB;">
<ul class="nav nav-list">
<li class="nav-header">
Site
</li>
<li><a href="https://fritzm.github.io/archives.html">Archives</a>
<li><a href="https://fritzm.github.io/tags.html">Tags</a>
<li><a href="https://fritzm.github.io/feeds/all.rss.xml" rel="alternate">RSS feed</a></li>
</ul>
</div>
<div class="well" style="padding: 8px 0; background-color: #FBFBFB;">
<ul class="nav nav-list">
<li class="nav-header">
Categories
</li>
<li><a href="https://fritzm.github.io/category/arcade-games.html">Arcade Games</a></li>
<li><a href="https://fritzm.github.io/category/math.html">Math</a></li>
<li><a href="https://fritzm.github.io/category/micros.html">Micros</a></li>
<li><a href="https://fritzm.github.io/category/pdp-11.html">PDP-11</a></li>
<li><a href="https://fritzm.github.io/category/programming.html">Programming</a></li>
<li><a href="https://fritzm.github.io/category/radios.html">Radios</a></li>
</ul>
</div>
<div class="social">
<div class="well" style="padding: 8px 0; background-color: #FBFBFB;">
<ul class="nav nav-list">
<li class="nav-header">
Social
</li>
<li><a href="http://facebook.com/fritzmueller">facebook</a></li>
<li><a href="http://instagram.com/infrafritz">Instagram</a></li>
<li><a href="http://www.linkedin.com/pub/fritz-mueller/a/679/62/">LinkedIn</a></li>
<li><a href="http://jsfiddle.net/user/fritzm/fiddles/">JSFiddle</a></li>
<li><a href="https://github.com/fritzm">GitHub</a></li>
</ul>
</div>
</div>
</div>
</div> </div>
<footer>
<br />
<p><a href="https://fritzm.github.io">fritzm.github.io</a> © Fritz Mueller 2023</p>
</footer>
</div> <!-- /container -->
<!-- Photoswipe -->
<div class="pswp" tabindex="-1" role="dialog" aria-hidden="true">
<div class="pswp__bg"></div>
<div class="pswp__scroll-wrap">
<div class="pswp__container">
<div class="pswp__item"></div>
<div class="pswp__item"></div>
<div class="pswp__item"></div>
</div>
<div class="pswp__ui pswp__ui--hidden">
<div class="pswp__top-bar">
<div class="pswp__counter"></div>
<button class="pswp__button pswp__button--close" title="Close (Esc)"></button>
<button class="pswp__button pswp__button--share" title="Share"></button>
<button class="pswp__button pswp__button--fs" title="Toggle fullscreen"></button>
<button class="pswp__button pswp__button--zoom" title="Zoom in/out"></button>
<div class="pswp__preloader">
<div class="pswp__preloader__icn">
<div class="pswp__preloader__cut">
<div class="pswp__preloader__donut"></div>
</div>
</div>
</div>
</div>
<div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
<div class="pswp__share-tooltip"></div>
</div>
<button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
</button>
<button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
</button>
<div class="pswp__caption">
<div class="pswp__caption__center"></div>
</div>
</div>
</div>
</div>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script src="https://fritzm.github.io/theme/bootstrap-collapse.js"></script>
</body>
</html>