{"id":788,"date":"2019-09-27T08:25:21","date_gmt":"2019-09-27T08:25:21","guid":{"rendered":"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/?page_id=788"},"modified":"2019-10-10T09:05:46","modified_gmt":"2019-10-10T09:05:46","slug":"performing-real-time-tasks-with-interrupts","status":"publish","type":"page","link":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/microcontrollers\/mbed-os-2\/courses\/level-5-embedded-and-real-time-systems\/performing-real-time-tasks-with-interrupts\/","title":{"rendered":"Performing Real-Time Tasks with Interrupts"},"content":{"rendered":"

Table of Contents<\/a><\/p>\n

\n

Interrupts – a first look<\/h1>\n

Although simple, polling has some major disadvantages:<\/p>\n

    \n
  1. It uses a lot of CPU resource even when there are no changes in the inputs. This is unlike most modern computer systems which are event driven and can idle.<\/li>\n
  2. The loop cycle time is variable (e.g. due to conditional statements). Therefore the \u201csampling interval\u201d of the inputs is not constant and is said to \u201cjitter\u201d. This can be a problem for certain types of input signal such as audio.<\/li>\n
  3. If the loop cycle is ever too long, input changes could be missed and data lost. The delay gets longer as more code is added.<\/li>\n
  4. Any blocking in the loop would result in inputs being ignored. For example, we cannot easily read the terminal in the polling loop and the C-Standard fgets<\/code> and scanf<\/code> are blocking functions.<\/li>\n<\/ol>\n

    \"\"<\/p>\n

     <\/p>\n

    \"\"<\/p>\n

    Note how the main loop simply puts the MCU in a low power sleep state. This means when there is nothing to do, the CPU does not waste cycles (and hence power). When the interrupt occurs, it wakes. This is the basis of event driven computing.<\/p>\n

    \"\"<\/p>\n

    This solution is an improvement, but still does not work perfectly.<\/p>\n

    Key Points:<\/strong><\/p><\/blockquote>\n

    This solution used two types of interrupt. One is driven from the GPIO and switch, the other from an internal hardware timer.<\/p>\n