title: What is the use of __IO & static keywords in C?
body: <p>I was checking out some code written for STM32F microcontroller and I found these keywords used before initializing a variable. I would like to know what is the significance of using this "<strong>__IO</strong>" &amp; "<strong>static</strong>" keywords? </p>
  
  <p>The line of code was given like that: </p>
  
  <pre><code>static   __IO   uint32_t   sysTickCounter; 
  </code></pre>