[CS61C FA20] Lecture 14.1 - Intro to Synchronous Digital Systems: Switches — Transcript

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1. 0:05oh
2. 0:06so sorry i didn't see you there welcome
3. 0:08to cs61c's lecture
4. 0:10on synchronous digital systems woo
5. 0:14great to have you back let's jump right
6. 0:16in we're talking about
7. 0:18switches so this is the picture you've
8. 0:22seen before
9. 0:22this is the layers of abstraction that
10. 0:25we talk about in old school machine
11. 0:27structures this course is called machine
12. 0:29structures and very as well
13. 0:30the great idea could be great ideas in
14. 0:32computer architecture so this talks
15. 0:34about
16. 0:34the action happens all around the middle
17. 0:36the isa the instruction set architecture
18. 0:39we kind of work our way down from the
19. 0:40top and we kind of work our way up from
20. 0:42the bottom
21. 0:43to to teach you how a complete computer
22. 0:46works and so we'll continue to do this
23. 0:48kind of going from the bottom up these
24. 0:49lectures are starting from the bottom
25. 0:50and working our way up
26. 0:52new school machine structures it's a
27. 0:53little more complicated
28. 0:55you've got a warehouse scale machine
29. 0:57which is breaking up broken up into
30. 0:59computers and that computer has multiple
31. 1:01cores in one of those cores you have
32. 1:03a processor that that's the kind of
33. 1:05piece of a processor of a core
34. 1:07execution units functional units memory
35. 1:10and then within that is
36. 1:11main within that is the logic gates
37. 1:14so when we talk about the parallelism on
38. 1:16the left we're mentioning there's a lot
39. 1:18we're going to eventually at the end by
40. 1:19the end of the year
41. 1:20teach you all five of these but for now
42. 1:22we're going to teach you the first one
43. 1:23which is
44. 1:24parallel hardware descriptions when you
45. 1:26say and
46. 1:28bitwise and of a and b 32
47. 1:31parallel and gates go and have the
48. 1:34output has another 32 bits so it's a 32
49. 1:37wide and gate bitwise and gate so how do
50. 1:40you even build that i don't even think
51. 1:41about that
52. 1:42probably you can imagine how to do that
53. 1:43just put 32 ands together but if you as
54. 1:45you get more complicated operations
55. 1:46we'll teach you how to do this in these
56. 1:47series of lectures
57. 1:48it's going to be kind of cool again here
58. 1:51is the
59. 1:51kind of new school way of thinking about
60. 1:53another way of looking at the layers of
61. 1:54abstraction from the languages to the
62. 1:56top
63. 1:56to the circuit levels at the bottom and
64. 1:58we're going to do everything below that
65. 1:59everything below the isa line we're
66. 2:01teaching in these series of lectures
67. 2:03this particular one is sts and then
68. 2:05we'll get there and we'll say okay now
69. 2:06we have blocks
70. 2:07i headed over to borah and borah's going
71. 2:08to take it over and talk about how to
72. 2:10then take those blocks and build
73. 2:12a running risk 5 computer that's amazing
74. 2:15so by the end of this you're going to
75. 2:16have a running risk drive computer to
76. 2:18run
77. 2:18the machine code you compiled assemble
78. 2:21and linked down to so this connection
79. 2:23day is going to be a really special day
80. 2:24and i can't wait till we get to that
81. 2:25stage 661c is a special course for that
82. 2:28reason
83. 2:29so we're talking about synchronous
84. 2:30digital systems let's let's kind of
85. 2:32decompact that and decompress that just
86. 2:34understand what those words mean
87. 2:35synchronous means you've got a heartbeat
88. 2:37you've got a heartbeat to the system
89. 2:39that heartbeat is your clock and that
90. 2:41clock operates probably nowadays in the
91. 2:43three or four gigahertz
92. 2:44range back when i was coming up uh it
93. 2:47was
94. 2:47100 megahertz and then 200 megahertz and
95. 2:49everyone kept saying oh my gosh three
96. 2:51can't wait till it's 400 and 500 then
97. 2:53when we hit a gig oh my gosh a gigahertz
98. 2:54what can you imagine
99. 2:56so four gigahertz means four billion
100. 2:58times a second that clock is going one
101. 3:00zero one zero as a square wave pretty
102. 3:02incredible pretty incredibly fast
103. 3:04um digital means you saw digital we
104. 3:06talked about analog to digital
105. 3:08conversions um digital means we're going
106. 3:10to take the
107. 3:11beautifully wonderful real world analog
108. 3:13values of voltage and current
109. 3:15and quantize them to be a zero and a one
110. 3:18and that's the idea that's what a bit
111. 3:19comes from
112. 3:20so when current is flowing we've got a
113. 3:22one current is not flowing
114. 3:24it's a zero pretty simple so we'll think
115. 3:26about that and talk about that
116. 3:27actually by going to the lowest level so
117. 3:28let's actually talk about
118. 3:30first logic designer then switches and
119. 3:32kind of the basics of that if you were
120. 3:33to do this at home you can by the way do
121. 3:35this at home with a
122. 3:36a bulb and a light the next slide or two
123. 3:38so in the next series of
124. 3:39several weeks we're gonna be talking
125. 3:41about how to build a processor we're
126. 3:42gonna
127. 3:43we talked about how to compile and link
128. 3:44assemble and link down to machine code
129. 3:46how do we even begin to think about
130. 3:48building a processor that can
131. 3:50run that code and actually execute it
132. 3:52flawlessly i mean flawlessly remarkable
133. 3:54never makes a mistake if
134. 3:56all the pieces work i have a working
135. 3:57risk five machine that should work
136. 3:59forever
137. 3:59amazing how do we do that well we're
138. 4:01going to start at the lowest level
139. 4:03hardware design it's great to understand
140. 4:06what this is it's i mean it's nice to be
141. 4:07able to for the same reason the 621a is
142. 4:09great you don't have to worry about how
143. 4:10memory management works or how
144. 4:12anything is you know what the run time
145. 4:14really is below the line maybe you do a
146. 4:15little bit
147. 4:16and then 6 to 1b we unpacked it a little
148. 4:18bit we teach you how still memory
149. 4:19management is covered for you
150. 4:21but you need to know what the size of
151. 4:22the you know this is a float this is a
152. 4:24double you need to know that you didn't
153. 4:25need to know that
154. 4:26certainly you need to know it at python
155. 4:28you could note about that you didn't
156. 4:29need to
157. 4:29as we get lower as we continue to reveal
158. 4:31the layers of the onion
159. 4:33it's great to not just stop at the isa
160. 4:35and say well somehow hardware does this
161. 4:37thing i don't know how it does it
162. 4:38it's great to actually understand what's
163. 4:40beneath the hood to be able to optimize
164. 4:42to be able to say oh wow that's how i
165. 4:44can optimize
166. 4:44the cache or use parallelism in
167. 4:46different ways or be able to know what
168. 4:48the limitations of a bid are this is why
169. 4:49this
170. 4:50course is so wonderful revealing all the
171. 4:51layers behind that were all abstracted
172. 4:53away from you in other courses so what
173. 4:56what are processors good at what are
174. 4:57processors bad at what can they do fast
175. 4:59what can't they so
176. 5:00avoid the slowed things and optimize for
177. 5:02the fast things they can do
178. 5:03um there are more courses beyond this
179. 5:05150 152 where courses you can take
180. 5:07beyond that i encourage you strongly to
181. 5:09think about that
182. 5:10um and there there are other things you
183. 5:12can do with other than just
184. 5:13take a processor from the store and use
185. 5:16it you could design your own processor
186. 5:17you can
187. 5:18design custom hardware for some task you
188. 5:20need to understand basics of hardware
189. 5:22and logic design
190. 5:23helps you give those tools to be able to
191. 5:24build that build that hardware pretty
192. 5:26cool
193. 5:26you walk you walk and you walk a little
194. 5:28taller once you learn this material like
195. 5:30wow i could actually build
196. 5:31any machine yeah you actually can after
197. 5:33these courses it's pretty pretty cool
198. 5:35so very basic let's we're going to walk
199. 5:38really slowly before we start to run
200. 5:40later
201. 5:41implement a simple circuit i think i did
202. 5:42this in third grade
203. 5:44where i had i folded up some aluminum
204. 5:46foil and i had this and i had a light
205. 5:48bulb from my i had a i had a flashlight
206. 5:49i took the light bulb out
207. 5:50and i had a i had a battery and then i
208. 5:53literally
209. 5:54taped the battery to this side and i
210. 5:55made a connection and so
211. 5:57we're going to actually start to use
212. 5:58some language that will help connect
213. 6:00this to the material a little later on
214. 6:02so we're going to see i have this
215. 6:05circuit
216. 6:06this is about let me actually use this
217. 6:07and give you a little bit of a thing
218. 6:09here
219. 6:10so this is the symbol for a battery
220. 6:13that's pretty cool um this is a symbol
221. 6:16for a light
222. 6:17and this is the symbol for a switch okay
223. 6:19so i've got my simple circuit i did
224. 6:21before i was in fourth grade
225. 6:22and the idea is we're going to consider
226. 6:25that switch
227. 6:26open to start with and we're going to
228. 6:28close it then
229. 6:29when i close it it forms a full circuit
230. 6:31and you probably remember this from
231. 6:33early you know experiments in in science
232. 6:35class
233. 6:36you have to have a closed circuit for
234. 6:37current to flow you can't have an open
235. 6:39circuit
236. 6:40so a closed circuit that means there's a
237. 6:42there's a way for a current to flow
238. 6:43around that and
239. 6:44current you can think of these electrons
240. 6:46are flowing from the battery they go
241. 6:48through the light they get the light
242. 6:49excited and they flow back and they go
243. 6:50back to the inside once
244. 6:52only when you have that that circuit
245. 6:53closed can you have any current flowing
246. 6:56and have that light go on
247. 6:58so when a that switch goes to set to one
248. 7:02we're going to say it's closed i now
249. 7:03have a closed circuit and now i have the
250. 7:05light goes going on
251. 7:07if a goes to zero by the way we're going
252. 7:08to call that also asserted when i assert
253. 7:11a so our cert means turn it to one or
254. 7:13close it in this particular case okay
255. 7:15so when i assert a light goes on when i
256. 7:18uninsert
257. 7:19a blink i open that that circuit that i
258. 7:21open that
259. 7:22switch it's now an open circuit now
260. 7:24there's no way for current to kind of
261. 7:26have a loop anymore
262. 7:27and because of that the light goes off
263. 7:29okay so we're going to say
264. 7:31that the brightness of z is connected to
265. 7:33a
266. 7:34one to one so now
267. 7:37can you actually wire some circuits to
268. 7:39do some logic you can and you could have
269. 7:40done this in fourth grade too
270. 7:42what if i had two switches and i lined
271. 7:44them up in serial
272. 7:46this is the first picture is in serial
273. 7:48well
274. 7:49i've got two switches here you might
275. 7:52think to yourself
276. 7:53when is there a closed circuit when can
277. 7:55when can there if there's a light in a
278. 7:57you know
279. 7:57a battery and a light as part of that
280. 7:59loop when is there a connection
281. 8:01there's again this is just replacing
282. 8:02that switch with this two here this is
283. 8:03showing the battery in the light anymore
284. 8:06well you can see that i only have
285. 8:08current to be able to flow when both
286. 8:10a and b i could have said this to a
287. 8:13fourth grader they say yeah when a
288. 8:14and b so they're already thinking about
289. 8:16kind of the logical sense of it they
290. 8:18probably don't even know what a truth
291. 8:19table is
292. 8:19but you realize they're only a closed
293. 8:21circuit when a and
294. 8:23b are both asserted closed so
295. 8:26here z is a and b all of a sudden just
296. 8:28thinking about switches connected to our
297. 8:30boolean logic it's pretty cool not still
298. 8:31a single bit
299. 8:32but it's pretty cool and this is wiring
300. 8:35them
301. 8:36in parallel so i don't care whether
302. 8:39current by the way current doesn't
303. 8:40either
304. 8:40current doesn't care whether it goes
305. 8:42through one or down the other one
306. 8:44through a or through b or through both
307. 8:46kermit's just happy to get from from
308. 8:47left side to the right side but from
309. 8:48right side to the left side
310. 8:50so this is a connection wiring them in
311. 8:52parallel gives me the
312. 8:53or gate the boolean one bit boolean or
313. 8:56gate
314. 8:57it's closed there's a path if a
315. 9:00or b are closed that's pretty cool so
316. 9:02already we're seeing a connection
317. 9:04between our switches our very basic
318. 9:06switches that again you could wire at
319. 9:08home with
320. 9:09some aluminum foil and a battery and a
321. 9:11light bulb from your flashlight
322. 9:13although they're now leds and so i don't
323. 9:15know if that still works but you know
324. 9:16maybe you can
325. 9:16connect it connect it to the leads of
326. 9:18your flashlight and say flashlight's
327. 9:19still going but you're connecting out
328. 9:21here and making some switches out here
329. 9:22you could do that it'd be really fun to
330. 9:23do and i'd love to see
331. 9:24please feel free to post on piazza with
332. 9:26pictures of yourself doing that that'd
333. 9:27be really fun
334. 9:28so anyway here's switches to boolean
335. 9:30logic pretty cool
336. 9:33let me just give a historical note
337. 9:34before we close this this set of lecture
338. 9:35this lecture off
339. 9:37um in the early days folks just build ad
340. 9:39hoc circuits and they were like oh
341. 9:40look what this does i look what this
342. 9:41does and then they say wait there's kind
343. 9:43of an andy thing going on and there's
344. 9:44kind of an ori thing going on this is
345. 9:46the early early days
346. 9:48it really wasn't until claude shannon uh
347. 9:51people consider claude shannon the
348. 9:53father of information systems
349. 9:55his master's thesis he was a brilliant
350. 9:57you know brilliant scholar and his
351. 9:58master's thesis made a connection
352. 10:00between transistors the thing he was
353. 10:01working on
354. 10:02and this mathematician back from the
355. 10:0519th century named george bull is a
356. 10:06picture of him on the bottom right
357. 10:08and he decided to call it boolean in his
358. 10:11honor
359. 10:12he made that connection says you know
360. 10:13what there's really some boolean natures
361. 10:15to it so
362. 10:15the word bullying came from that
363. 10:17connection between george bull
364. 10:19and the work that he was doing in
365. 10:20transistors is pretty cool and we
366. 10:22arrived and
367. 10:22we realized through that connection we
368. 10:24realized now we can use mathematics
369. 10:25to do amazing things like hardware
370. 10:27design minimization
371. 10:28um boolean boolean algebra
372. 10:32models of circuits all these things
373. 10:33we'll teach you in these series of
374. 10:35lectures
375. 10:35and that connection was again made by
376. 10:36claude shannon pretty cool we'll see the
377. 10:38next lecture we're talking about
378. 10:39transistors see you then