1 00:00:01,100 --> 00:00:02,340 Hello, welcome back. 2 00:00:02,810 --> 00:00:09,440 In this lesson, we shall see how to work with binary semaphores, I have gone ahead to create a new 3 00:00:09,440 --> 00:00:12,320 project here at number 18, binary semaphores. 4 00:00:12,710 --> 00:00:18,140 And this NMT project is Jesco, our Ewart's in our system clock. 5 00:00:18,140 --> 00:00:21,830 In it, there is no ARTUS code here. 6 00:00:22,010 --> 00:00:23,450 We're going to add that together. 7 00:00:23,720 --> 00:00:25,580 This Jesco our Ewart's. 8 00:00:26,540 --> 00:00:32,720 And our system look like I said, OK, so what are we going to do is we going to start off by having 9 00:00:32,720 --> 00:00:41,150 three tasks and we're going to let them all access the, um, the the support at the same time and we'll 10 00:00:41,150 --> 00:00:42,040 see what happens. 11 00:00:42,560 --> 00:00:48,010 But before we use semaphores, we have to include the semaphores header file in our project. 12 00:00:48,500 --> 00:00:54,080 So I'm going to come to our Simms's, always start over here, highlight's this and then. 13 00:00:54,470 --> 00:00:56,720 Right, click select open declaration. 14 00:00:58,910 --> 00:01:05,000 And down here where I have all of the artists component, I'm going to include one for semaphores, 15 00:01:05,450 --> 00:01:14,210 I'll include I can just copy this and then paste it over here and rename this word to semaphores s m 16 00:01:14,450 --> 00:01:20,000 p h are such that we have semaphores that each like this. 17 00:01:22,930 --> 00:01:30,880 Once that is done, I'm going to come over here to may not see and then I'm going to start off by creating 18 00:01:30,880 --> 00:01:31,870 three tasks. 19 00:01:32,380 --> 00:01:34,810 Let's say these are the controller tasks. 20 00:01:35,230 --> 00:01:40,570 We're going to have one for blue, one for yellow and one for red. 21 00:01:41,590 --> 00:01:44,260 So I'll create those tasks. 22 00:01:45,100 --> 00:01:48,690 Each task would have a stack size of one hundred and two. 23 00:01:48,700 --> 00:01:51,500 All have the same priority. 24 00:01:51,550 --> 00:01:55,300 So this what we have, we have three tasks created. 25 00:01:56,310 --> 00:02:02,250 We have read a little controller task yellowbelly the controller task and then the controller task is 26 00:02:02,250 --> 00:02:05,800 the name were given the task function that we should implement later. 27 00:02:06,450 --> 00:02:09,270 We also going to create a binary semaphore. 28 00:02:10,320 --> 00:02:16,260 Before we do that, we're going to declare a Hando to hold the binary SEMAFO, I'm going to copy this 29 00:02:17,100 --> 00:02:17,640 and. 30 00:02:19,330 --> 00:02:25,630 Paste over here, we have X binary SEMAFO, that's the name of the SEMAFO Hondo, I'm also going to 31 00:02:25,630 --> 00:02:30,820 declare task profiler's that we shall use to profile our tasks. 32 00:02:31,770 --> 00:02:39,450 So we're going to have one for each we first use TYPEDEF to rename it to task profiler's such that whenever 33 00:02:39,450 --> 00:02:42,840 we want to see it, we can simply type this word. 34 00:02:42,840 --> 00:02:49,800 Task profiler, I'm going to declare red profile, yellow ality profile and blue ality profiler, and 35 00:02:49,800 --> 00:02:54,120 we shall drop each profiler in each of the task functions. 36 00:02:55,640 --> 00:03:03,740 So once we've created our tasks and our semaphores, we go ahead and start the scheduler and we do this, 37 00:03:03,740 --> 00:03:05,330 of course, using our V task. 38 00:03:07,250 --> 00:03:09,350 Start such a function like this. 39 00:03:09,590 --> 00:03:17,000 OK, so now we have to implement the task functions, we start off with the first one, we're going 40 00:03:17,000 --> 00:03:19,220 to have the red alert controller task. 41 00:03:21,030 --> 00:03:25,740 And then it's going to have the wah wah loop in here, the infinite loop. 42 00:03:27,720 --> 00:03:38,310 OK, and then we going to copy this and then I'll change the word read here to Blue Sajdah, we create 43 00:03:38,310 --> 00:03:41,430 the task function for blue ality controller. 44 00:03:42,610 --> 00:03:49,660 And then I'm going to paste this over here and then change the word red to yellow. 45 00:03:53,040 --> 00:03:55,440 Such that we have yellow controller. 46 00:03:57,180 --> 00:04:01,110 I'm going to copy the function prototypes and put them on the topia. 47 00:04:02,410 --> 00:04:03,610 This is the one for red. 48 00:04:05,990 --> 00:04:07,220 This is the one for blue. 49 00:04:09,800 --> 00:04:11,900 And then we grabbed the one for yellow. 50 00:04:13,930 --> 00:04:18,580 Like this and also remember, all our tasks have the same priority. 51 00:04:19,790 --> 00:04:20,290 OK. 52 00:04:22,290 --> 00:04:27,150 So what are we going to do is we going to drop the profiler's in each of them? 53 00:04:29,250 --> 00:04:35,160 So I'm going to copy, read a little profiler, and then I'll come over here to read aloud and then 54 00:04:35,160 --> 00:04:40,010 I'll C++, then I'm going to grab yellowbelly the profiler. 55 00:04:40,890 --> 00:04:41,760 Now come here. 56 00:04:43,370 --> 00:04:47,660 And yellow led and then plus plus, you know, grup. 57 00:04:48,590 --> 00:04:52,010 Blue lady profiler will come here in blue. 58 00:04:53,510 --> 00:04:54,980 And then plus, plus. 59 00:04:56,620 --> 00:04:57,880 Put a semicolon here. 60 00:05:02,450 --> 00:05:03,020 OK. 61 00:05:05,200 --> 00:05:12,310 So currently, our tasks does just one thing, it's incremental, this global variable, each of them 62 00:05:12,310 --> 00:05:14,620 have their own global variables that the increment. 63 00:05:15,220 --> 00:05:20,200 But we what are we going to do is we're going to let each task take the SEMAFO we've created. 64 00:05:21,200 --> 00:05:27,380 They take the SEMAFO and then they go ahead to increment their respective global variable, if they've 65 00:05:27,380 --> 00:05:29,440 not taken a SEMAFO, they cannot do that. 66 00:05:30,020 --> 00:05:34,400 So I'm going to surround each increment with our. 67 00:05:37,420 --> 00:05:39,970 Which our semaphore code so red. 68 00:05:41,400 --> 00:05:47,640 Task would take the SEMAFO, the name of our SEMAFO is extraordinary SEMAFO, and then we say Portsmouth's 69 00:05:47,650 --> 00:05:49,890 delay give given the maximum delay here. 70 00:05:49,890 --> 00:05:55,530 So it would first have to take the SEMAFO before its increment once it's done incrementing. 71 00:05:57,100 --> 00:06:07,630 We can go ahead and give back to SEMAFO and then the next task will take the SEMAFO Blue and then it 72 00:06:07,630 --> 00:06:13,180 would after is taken to semaphores you go ahead and run its code, which is simply to increment its 73 00:06:13,180 --> 00:06:14,020 global variable. 74 00:06:14,170 --> 00:06:17,920 Once it's done, it will give back to semaphores so that the next one can take it. 75 00:06:18,310 --> 00:06:22,150 The next the final, which is the next is this one yellow. 76 00:06:22,180 --> 00:06:23,290 It will take the SEMAFO. 77 00:06:23,650 --> 00:06:26,070 Once it is done, it will give back to some awful. 78 00:06:27,910 --> 00:06:30,710 OK, let's run this and see what we have. 79 00:06:31,390 --> 00:06:33,250 I'm going to click over here to build. 80 00:06:40,540 --> 00:06:41,780 It's built successfully. 81 00:06:41,890 --> 00:06:49,660 I'm going to right click and see debuggers ASTM 32, Coatex M iSelect 18 over here. 82 00:06:51,510 --> 00:06:52,500 And then OK. 83 00:06:58,700 --> 00:07:00,440 Then I'll click switch over here. 84 00:07:03,580 --> 00:07:10,470 And what I'm going to do is come to our live expressions window over here are clear, OK? 85 00:07:12,100 --> 00:07:21,100 OK, everything about that, Cledus, and then let's add our profiler's again, red profiler, we are 86 00:07:21,370 --> 00:07:22,870 yellow profiler. 87 00:07:26,080 --> 00:07:27,850 We are blue profiler. 88 00:07:29,920 --> 00:07:31,960 OK, I'm going to click to run Elkwood. 89 00:07:33,330 --> 00:07:34,440 I'm running out code. 90 00:07:36,640 --> 00:07:37,670 But nothing is happening. 91 00:07:37,690 --> 00:07:41,200 I'm going to click to pause to see what the issue may be. 92 00:07:42,730 --> 00:07:46,180 Well, OK, we're running around, could it? 93 00:07:46,350 --> 00:07:53,950 Yes, because we are brought to the kudos for being in a separate program is being executed here. 94 00:07:56,920 --> 00:07:57,850 Oh, stop this. 95 00:07:59,630 --> 00:08:01,940 We do not have an AQ code here. 96 00:08:08,510 --> 00:08:13,970 So I'm going to right, click on binary semaphore projects and then build again. 97 00:08:15,020 --> 00:08:15,920 They would project. 98 00:08:17,380 --> 00:08:22,660 It's built successfully, right, click, debug us, select this. 99 00:08:23,640 --> 00:08:26,760 And then a select number 18, see? 100 00:08:32,420 --> 00:08:33,730 Then switch. 101 00:08:39,260 --> 00:08:41,090 And then I'm going to click to run. 102 00:08:43,080 --> 00:08:45,420 We still stuck our collective paws. 103 00:08:47,830 --> 00:08:49,700 And we are brought to the queue again. 104 00:08:50,330 --> 00:08:51,400 OK, let's find out. 105 00:08:53,910 --> 00:08:54,840 We're going to stop this. 106 00:08:56,880 --> 00:09:03,040 OK, so it's an anomaly which we've committed before or I have committed before. 107 00:09:03,420 --> 00:09:08,000 So when we came here, I mentioned we've created a SEMAFO, but we actually haven't. 108 00:09:08,820 --> 00:09:10,710 I failed to create the SEMAFO. 109 00:09:10,710 --> 00:09:14,380 So that is why we are being sent to that location whenever we post. 110 00:09:14,760 --> 00:09:22,830 So over here, reinitialize we print system in it and we create our SEMAFO X creates binary. 111 00:09:22,830 --> 00:09:28,020 And then we started Hando in our semaphore Hondo before we go ahead to create our tasks. 112 00:09:28,770 --> 00:09:30,960 So I'll click here to build. 113 00:09:33,000 --> 00:09:34,230 It's argued successfully. 114 00:09:35,900 --> 00:09:37,640 I'll click to go to debark. 115 00:09:43,700 --> 00:09:45,140 And then switch. 116 00:09:49,340 --> 00:09:51,290 OK, now a click to run. 117 00:09:56,920 --> 00:09:58,240 OK, let's pause and see. 118 00:10:00,650 --> 00:10:01,630 I said no. 119 00:10:01,700 --> 00:10:02,530 Over here. 120 00:10:04,430 --> 00:10:05,660 Exhumed pended. 121 00:10:05,920 --> 00:10:07,130 OK, I'm going to stop. 122 00:10:09,850 --> 00:10:17,380 No, what we've just experienced is a very common issue in real time operating systems when dealing 123 00:10:17,380 --> 00:10:25,720 with semaphores and other things like mutex, which are a form of SEMAFO, what we are experiencing 124 00:10:25,720 --> 00:10:30,170 now is known as a deadlock or a deadly embrace. 125 00:10:30,640 --> 00:10:31,460 Let me explain. 126 00:10:32,530 --> 00:10:38,600 So you see, we start over here by creating the Red Alyda controller task. 127 00:10:39,400 --> 00:10:43,180 So this is going to be the first task to run since they all have equal priority. 128 00:10:43,780 --> 00:10:50,260 When this task tries to run, it would come over here expecting to receive a SEMAFO because we have 129 00:10:50,260 --> 00:10:51,490 the Zema for take. 130 00:10:53,890 --> 00:10:55,960 But no one is given the SEMAFO. 131 00:10:57,100 --> 00:11:04,810 So this function wants to take a SEMAFO and then run its code and then give back to SEMAFO, but before 132 00:11:04,810 --> 00:11:07,980 it takes the SEMAFO, the SEMAFO has to be given. 133 00:11:08,680 --> 00:11:12,580 So essentially all our tasks are waiting for a SEMAFO. 134 00:11:13,240 --> 00:11:15,220 Each of them can give us a map for once. 135 00:11:15,220 --> 00:11:16,420 They've taken it by. 136 00:11:16,420 --> 00:11:23,230 They are waiting for each of them to give the SEMAFO because if our function started from give the next 137 00:11:23,230 --> 00:11:28,810 function, if our task gave the SEMAFO, then this blue could take it. 138 00:11:29,440 --> 00:11:34,340 Essentially each of them are waiting for a resource that they all have access of providing. 139 00:11:34,900 --> 00:11:42,790 So someone has to give the SEMAFO first to to get the ball rolling without starting by giving the SEMAFO, 140 00:11:42,790 --> 00:11:49,090 we would be kept in this deadlock where each task has the ability to give and take the SEMAFO, but 141 00:11:49,090 --> 00:11:50,020 no one is given. 142 00:11:50,710 --> 00:11:53,130 And because no one is given, no one can take. 143 00:11:53,860 --> 00:11:55,300 So what are we going to do is. 144 00:11:56,770 --> 00:11:59,410 We're going to start off when our program starts. 145 00:12:01,500 --> 00:12:07,380 In a red ality, not in our well-worn loop, but in the Red Élodie task, we're going to start off by 146 00:12:07,380 --> 00:12:13,020 giving the SEMAFO so read the function would first give the SEMAFO and then the wall one loop. 147 00:12:13,170 --> 00:12:15,320 We take the SEMAFO and then we proceed. 148 00:12:15,690 --> 00:12:18,290 Let's see if this will solve our Dedlock problem. 149 00:12:18,690 --> 00:12:19,830 I'll click here to build. 150 00:12:27,500 --> 00:12:30,710 It's built successfully, click here to go to the few. 151 00:12:34,500 --> 00:12:35,310 Click to switch. 152 00:12:39,540 --> 00:12:46,800 OK, I'll click here to run, and now as you can see, we have all of our tasks running and we know 153 00:12:46,800 --> 00:12:51,840 it's running because they are all incrementing profiles and you see that they are run in almost equal 154 00:12:51,840 --> 00:12:56,400 amount of time, not entirely equal because one has to. 155 00:12:57,670 --> 00:13:03,340 Perform its computation and then give the SEMAFO for the other one to perform its computation, but 156 00:13:03,370 --> 00:13:05,500 we see that they are all running right. 157 00:13:06,240 --> 00:13:06,700 OK. 158 00:13:07,960 --> 00:13:14,130 They are running what we are going to do is now we've verified that they are all running with a semaphore. 159 00:13:14,140 --> 00:13:19,150 We're going to say when Red takes the SEMAFO red ones, give it back. 160 00:13:19,180 --> 00:13:21,220 So we're going to comment on this line. 161 00:13:21,700 --> 00:13:23,200 Going to click here to build. 162 00:13:27,190 --> 00:13:30,490 It's built successfully, we click here to go to the debug view. 163 00:13:37,190 --> 00:13:38,870 And then we click here to switch. 164 00:13:42,400 --> 00:13:44,500 And then we click here to run. 165 00:13:46,700 --> 00:13:55,490 Now you see that red round was red, just executed once, but it's executed once and got stuck. 166 00:13:55,520 --> 00:13:56,040 Why? 167 00:13:56,210 --> 00:14:00,890 Because when we take a look at our code red took the SEMAFO. 168 00:14:01,880 --> 00:14:03,710 And then it's executed. 169 00:14:05,010 --> 00:14:11,280 And now no one is given the semaphore, Red was supposed to give the semaphore to the next task to run 170 00:14:11,730 --> 00:14:17,820 and then also give the SEMAFO, but because Red didn't give the SEMAFO after its execution, nothing 171 00:14:17,820 --> 00:14:18,870 else is executed. 172 00:14:19,590 --> 00:14:19,980 Right. 173 00:14:20,580 --> 00:14:22,530 So this is another observation. 174 00:14:23,630 --> 00:14:25,800 OK, so we're going to bring this back. 175 00:14:26,090 --> 00:14:31,540 Now, what are we going to do is we go into print zero data. 176 00:14:31,550 --> 00:14:38,150 We're going to let each of the task access the support and print a piece of information read is going 177 00:14:38,150 --> 00:14:48,110 to print this red task and then yellow will print this yellow task and then blue print its own piece 178 00:14:48,110 --> 00:14:49,500 of information. 179 00:14:50,090 --> 00:14:56,360 So this is yellow task from yellow and then blue over here would say. 180 00:14:58,940 --> 00:15:03,010 This is blue Tosk, so this what we have, OK? 181 00:15:06,090 --> 00:15:08,970 So we click over here to build. 182 00:15:11,910 --> 00:15:12,540 And then. 183 00:15:13,530 --> 00:15:14,790 We click here to run. 184 00:15:18,850 --> 00:15:20,950 OK, I'm going to open real term. 185 00:15:24,190 --> 00:15:30,250 This is from our old project, I'm going to Claire and then click to open the port. 186 00:15:32,530 --> 00:15:38,090 Let's see what we have, we have this is red TASC, this is red task, this is red. 187 00:15:38,470 --> 00:15:39,840 How about the rest? 188 00:15:39,850 --> 00:15:40,510 Let's see. 189 00:15:42,670 --> 00:15:43,270 Let's see. 190 00:15:45,370 --> 00:15:49,450 So let's see, so we have this we have just the. 191 00:15:52,330 --> 00:15:55,510 The Red Cross printed its information over here. 192 00:15:55,660 --> 00:16:05,350 OK, so let's see if only the red thread or task is the one executed by observing the profiler's. 193 00:16:05,860 --> 00:16:09,710 That's the way you try to diagnose problems in the real time system. 194 00:16:10,210 --> 00:16:15,520 So I'm going to click here to go to the box you and we're going to see if our profiles are not changing. 195 00:16:19,800 --> 00:16:25,690 So I'm going to come over here, click here to run, and we have just read a little profiler running. 196 00:16:26,430 --> 00:16:28,470 OK, let's see what we have. 197 00:16:34,900 --> 00:16:41,950 So Red takes the the SEMAFO and Red gives the semaphore. 198 00:16:43,280 --> 00:16:50,180 Lou takes the SEMAFO, the blue gives it, however, only red is running, let's comment at our printf 199 00:16:50,180 --> 00:16:52,900 and see if that would solve the issue. 200 00:16:52,910 --> 00:16:56,840 I'm going to comment on the premise that we just added. 201 00:16:57,770 --> 00:16:59,450 Then I'm going to click here to build. 202 00:17:02,670 --> 00:17:03,750 Secured successfully. 203 00:17:05,200 --> 00:17:07,540 Then we click here to go to debark few. 204 00:17:15,490 --> 00:17:16,420 Click here to switch. 205 00:17:21,670 --> 00:17:23,810 Then I'm going to click here to run. 206 00:17:24,290 --> 00:17:26,240 OK, so now it's running. 207 00:17:28,670 --> 00:17:37,400 OK, so with the with a printer to use the printer with stability, I'm going to add the task delay 208 00:17:37,400 --> 00:17:39,530 of one to each function. 209 00:17:40,250 --> 00:17:44,390 OK, so I'm simply going to advertise this one here. 210 00:17:50,130 --> 00:17:53,250 OK, so read LDV Task DeLay. 211 00:17:54,700 --> 00:17:57,610 I'm going to do the same for Lou. 212 00:17:58,650 --> 00:18:01,290 Then I'm going to do the same for yellow. 213 00:18:03,370 --> 00:18:05,620 Like this, and then I'm going to click here to run. 214 00:18:16,690 --> 00:18:19,240 People suggesting that I'm going to. 215 00:18:20,280 --> 00:18:23,060 Yeah, that's straight by running Facebook, click here to read. 216 00:18:26,450 --> 00:18:29,390 It's a 20 to percent year like computer running low. 217 00:18:31,470 --> 00:18:32,860 OK, it's finished running. 218 00:18:32,880 --> 00:18:34,080 Let's see real tim. 219 00:18:35,540 --> 00:18:42,200 OK, I'm going to open the port and now you can see we have each and every one of them type in their 220 00:18:42,200 --> 00:18:49,910 respective message, we have over here Red TASC, Blue TASC, Yellow TASC, Red Task, blue tasc, yellow 221 00:18:49,910 --> 00:18:52,600 tasc, red, blue, yellow, red, blue. 222 00:18:52,610 --> 00:18:55,160 It's all that one after the other. 223 00:18:55,610 --> 00:19:00,010 OK, so let's see what happens when we see no more semaphores. 224 00:19:00,020 --> 00:19:02,000 We don't need semaphores in our system. 225 00:19:04,560 --> 00:19:12,330 We're going to comment out the SEMAFO take and SEMAFO give functions in our code, in all of the tasks 226 00:19:12,870 --> 00:19:18,960 read, and now we comment it out of blue and then we comment it out of yellow as well. 227 00:19:19,200 --> 00:19:19,800 Like this. 228 00:19:21,300 --> 00:19:23,820 Once that is done, I'm going to click here to build. 229 00:19:26,040 --> 00:19:33,450 It's built successfully and I'm going to click here to run and then I'm going to open to. 230 00:19:37,390 --> 00:19:39,190 It's still downloading onto the board. 231 00:19:40,610 --> 00:19:49,100 It's done downloading, going to open real time here, OK, real time is opened, but this is what we 232 00:19:49,100 --> 00:19:49,580 get now. 233 00:19:49,610 --> 00:19:56,810 It's jumbled up, right, because all of the threads are trying to access the serial port. 234 00:19:57,980 --> 00:20:04,730 Meanwhile, the support is a single resource one has to access at the time we were using the SEMAFO 235 00:20:05,180 --> 00:20:08,030 to enable, there is just a single access. 236 00:20:08,210 --> 00:20:11,600 You can think of the support or the you ought to be a bathroom. 237 00:20:11,900 --> 00:20:13,610 You can have just one occupant. 238 00:20:14,150 --> 00:20:19,910 The occupant has to take the key, opened the door, use the bathroom and then return to key. 239 00:20:20,660 --> 00:20:28,760 Taking the key is similar to our semaphore take function here and then printing this yellow task is 240 00:20:28,760 --> 00:20:30,220 like using the bathroom. 241 00:20:30,230 --> 00:20:33,350 And once you are done, you come out of the bathroom and you give back. 242 00:20:33,350 --> 00:20:38,750 The key is similar to our SEMAFO give back because now the door is open. 243 00:20:38,750 --> 00:20:40,370 There is no key associated. 244 00:20:41,060 --> 00:20:45,110 Everyone is trying to enter the bathroom and mess it up at the same time. 245 00:20:45,140 --> 00:20:48,190 So we have this type of display on our zero program. 246 00:20:48,650 --> 00:20:53,450 Okay, so obviously the best thing to do in this case is to use the SEMAFO. 247 00:20:53,750 --> 00:21:00,890 We would see rather than have semaphore take and SEMAFO Give would see a semaphore mutex that allows 248 00:21:00,890 --> 00:21:04,070 us to use a single API to. 249 00:21:05,380 --> 00:21:11,830 To do the same thing that we use in these two SEMAFO APIs, take and give to achieve, we use the mutex 250 00:21:11,830 --> 00:21:16,390 to to achieve the same thing, but this time we'll call a single function. 251 00:21:17,040 --> 00:21:24,520 OK, but we've seen the the benefits of semaphores over here in accessing shared resources and we've 252 00:21:24,520 --> 00:21:28,130 seen how semaphores can be used to block a part of code as well. 253 00:21:28,690 --> 00:21:31,360 So we've done a number of experiments with semaphores. 254 00:21:31,360 --> 00:21:38,710 I would just build our projects again and take it back to its SEMAFO nature before we conclude this 255 00:21:38,710 --> 00:21:42,820 particular lesson of with the project go into. 256 00:21:44,390 --> 00:21:45,380 Click here to run. 257 00:21:51,900 --> 00:21:53,280 It's downloading onto the board. 258 00:21:55,030 --> 00:21:55,930 I'll clear this. 259 00:21:59,910 --> 00:22:07,860 And it says waiting for the debugger and then we have 97 percent here to almost complete. 260 00:22:09,400 --> 00:22:12,730 OK, it's complete now I'm going to open our port. 261 00:22:14,560 --> 00:22:19,150 And I'm going to open again, and as you can see, we are back to normal operation. 262 00:22:23,420 --> 00:22:32,420 OK, this happens when you try to restart the port in the middle of a transfer, so we are back to red, 263 00:22:32,420 --> 00:22:34,760 yellow, blue, red, yellow, blue again. 264 00:22:35,000 --> 00:22:39,170 OK, so this order is we've explored binary semaphores. 265 00:22:39,890 --> 00:22:41,210 That's all there is for this lesson. 266 00:22:41,210 --> 00:22:44,210 If you have any questions, leave them in the questions and answers area. 267 00:22:44,270 --> 00:22:45,020 I'll see you later. 268 00:22:45,050 --> 00:22:45,770 Have a nice day.