1 00:00:01,280 --> 00:00:01,680 Hello. 2 00:00:01,700 --> 00:00:02,410 Welcome back. 3 00:00:02,420 --> 00:00:06,980 In this lesson we shall give a brief overview of interrupt programming. 4 00:00:06,980 --> 00:00:11,420 A single microprocessor can save several devices. 5 00:00:11,420 --> 00:00:13,850 There are two ways to do this. 6 00:00:13,880 --> 00:00:21,540 We can either use interrupt or pull in method in the interrupt method whenever any device needs servers. 7 00:00:21,590 --> 00:00:26,640 The device notifies DCP by sending it an interrupt signal. 8 00:00:26,780 --> 00:00:28,810 Receive an uninterrupted signal. 9 00:00:28,850 --> 00:00:33,970 The CPD you interrupt whatever it is doing and serves the device. 10 00:00:34,040 --> 00:00:41,750 The program associated with the interrupt is called the interrupt service routine or the ISI or the 11 00:00:41,750 --> 00:00:45,390 interrupt handler in pulling the seat. 12 00:00:45,390 --> 00:00:51,590 You continuously monitors the status of a given device when the status condition is met. 13 00:00:51,590 --> 00:00:53,690 The CPSU performs the service. 14 00:00:53,690 --> 00:01:00,000 After that the CPM moves to monitor the next device until each one is serviced. 15 00:01:00,000 --> 00:01:08,270 Poland is often characterized by things like if conditions or do polling can monitor the status of several 16 00:01:08,270 --> 00:01:13,790 devices and serve each of them assets and conditions are met. 17 00:01:13,790 --> 00:01:17,390 It is not an efficient use of the time. 18 00:01:17,510 --> 00:01:25,190 The pooling method wastes much of the CPE use time by pooling devices that do not need service. 19 00:01:25,280 --> 00:01:32,940 So in order to avoid tying down to sleep you interrupt are used for instance in a timer. 20 00:01:32,960 --> 00:01:39,850 We might wait until a determined amount of time elapses and while waiting. 21 00:01:39,890 --> 00:01:42,430 We cannot do anything else. 22 00:01:42,470 --> 00:01:49,160 This is a waste of the CPS time that could have been used to perform some useful tasks. 23 00:01:49,160 --> 00:01:56,330 On the other hand if we use the interrupt method the CPR you can go about doing other tasks and when 24 00:01:56,330 --> 00:02:04,250 the count flag is raised the timer will interrupt the CPE you to let him know that the time is elapsed. 25 00:02:04,370 --> 00:02:10,650 Like I mentioned earlier for every interrupt there must be a program associated with it. 26 00:02:10,820 --> 00:02:17,900 When an interrupt occurs this program is executed to perform a certain service for the interrupt this 27 00:02:17,900 --> 00:02:25,370 program is commonly referred to as the interrupt service routine or the IRS are or the interrupt handler 28 00:02:26,030 --> 00:02:28,290 as we can see in this arrangement. 29 00:02:28,430 --> 00:02:35,870 In the process or there are pieces that are associated with the hardware interrupt I are cute over here 30 00:02:36,350 --> 00:02:37,850 stands for interrupt. 31 00:02:37,850 --> 00:02:50,320 So we have IQ zero IQ so we have IQ zero IQ one all the way through IQ and these are input signals into 32 00:02:50,320 --> 00:02:59,140 the CPI you when the signals are triggered the CPI pushes the program counter register or the P.C. onto 33 00:02:59,140 --> 00:03:04,960 the stock and loads the program counter register with the address of the interrupt service routine. 34 00:03:04,960 --> 00:03:12,320 This causes the interrupt service routine to be executed this table over here shows what is known as 35 00:03:12,320 --> 00:03:18,980 the interrupt effect or on the left we've got the one for cortex M0 plus and on the right we've got 36 00:03:18,980 --> 00:03:27,770 the ones for the one for cortex and for an M M7 this image is taken from the generic user guide and 37 00:03:27,770 --> 00:03:33,880 we can find a similar table in or cortex and microcontroller data sheet. 38 00:03:33,980 --> 00:03:36,870 The first column here says exception no. 39 00:03:36,890 --> 00:03:39,080 The next column says the interrupt. 40 00:03:39,090 --> 00:03:39,690 No. 41 00:03:39,740 --> 00:03:46,380 The third column says the offset and the fourth column sees the effect all you can think of the effect 42 00:03:46,380 --> 00:03:53,050 or us the name of the interrupt as we can tell from the offset for every interrupt. 43 00:03:53,060 --> 00:03:58,160 There are four byte of memory allocated in the interrupt vector table. 44 00:03:58,160 --> 00:04:04,910 These four memory locations provide the addresses of the interrupt service routine for which the interrupt 45 00:04:04,910 --> 00:04:12,160 was invoked the end Vic is known as the nested effect or interrupt controller. 46 00:04:12,300 --> 00:04:19,110 The end Vic of the cortex M has room for a total of two hundred and fifty five interrupt and exceptions 47 00:04:19,450 --> 00:04:26,200 the end of the can and cortex and assigns the first fifteen interrupt for internal use. 48 00:04:26,220 --> 00:04:34,820 Now let's take a look at interrupt prioritise in the cortex in the Reset. 49 00:04:34,940 --> 00:04:37,520 And then my in hard fought exceptions. 50 00:04:37,520 --> 00:04:47,370 How fixed priority levels are set by itself and cannot be changed among the reset and in my end hard 51 00:04:47,370 --> 00:04:52,400 fought the reset has the highest priority which is minus 3. 52 00:04:52,590 --> 00:04:56,370 The lower the number the higher the priority. 53 00:04:56,370 --> 00:05:05,340 For instance if Booth and my and a different interrupt which is not reset are activated at the same 54 00:05:05,340 --> 00:05:14,170 time the enemy is responded to first since the enemy has a higher priority than other interrupt requests. 55 00:05:14,290 --> 00:05:21,840 Apart from the reset interrupts request the rest of the exceptions and interrupts request help lower 56 00:05:21,840 --> 00:05:31,880 priorities and configurable meaning priority levels can be set by We The program is programmable priority 57 00:05:31,880 --> 00:05:40,910 levels are values between 0 and 7 with 7 as the lowest priority that we can set and 0 as the highest 58 00:05:40,910 --> 00:05:43,650 priority that we can set. 59 00:05:43,890 --> 00:05:45,770 So this order is for this very short. 60 00:05:45,780 --> 00:05:53,040 Both of you on interrupt you have any questions just let me know and I shall see you in the next lesson.