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<h1 id="firstHeading" class="firstHeading">How to handle an interrupt</h1>
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<h3 id="siteSub">From Milkymist Wiki</h3>
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<div id="jump-to-nav">Jump to: <a href="index.php%3Ftitle=How_to_handle_an_interrupt.html#column-one">navigation</a>, <a href="index.php%3Ftitle=How_to_handle_an_interrupt.html#searchInput">search</a></div> <!-- start content -->
<p>WIP some snipets from [slides| <a href="http://lekernel.net/presentations/masteri2l/conf/mm_i2l.pdf" class="external free" title="http://lekernel.net/presentations/masteri2l/conf/mm_i2l.pdf" rel="nofollow">http://lekernel.net/presentations/masteri2l/conf/mm_i2l.pdf</a>]
</p><p>Interruptions.
</p><p>Example&nbsp;: serial port
</p>
<ul><li> Register at 0xe0000000.
</li></ul>
<ul><li> Interruption 0 after a character is received
</li><li> Interruption 1 after a character is received sent
</li></ul>
<pre>void transmit(char c)
{
/* write a character */
*((volatile unsigned int *)0xe0000000) = c;
/* after a character is received */
while(!(lm32_interrupts_pending() &amp; (1 &lt;&lt; 0)));
/* acknowledge interrupt */
lm32_interrupt_ack(1 &lt;&lt; 0);
}
</pre>
<pre>char receive()
{
/* reception loop */
while(!(lm32_interrupts_pending() &amp; (1 &lt;&lt; 1)));
/* acknowledge interruption */
lm32_interrupt_ack(1 &lt;&lt; 1);
/* read character */
return *((volatile unsigned int *)0xe0000000);
}
</pre>
<p><br />
You need some asm at startup <a href="https://github.com/milkymist/milkymist/blob/master/software/bios/crt0.S#L63" class="external free" title="https://github.com/milkymist/milkymist/blob/master/software/bios/crt0.S#L63" rel="nofollow">https://github.com/milkymist/milkymist/blob/master/software/bios/crt0.S#L63</a>
</p><p>Then a interrupt service routine, a software routine that is executed in response to an interrupt <a href="https://github.com/milkymist/milkymist/blob/master/software/bios/isr.c#L32" class="external free" title="https://github.com/milkymist/milkymist/blob/master/software/bios/isr.c#L32" rel="nofollow">https://github.com/milkymist/milkymist/blob/master/software/bios/isr.c#L32</a>
</p><p>And the lib for uart for this example in this case <a href="https://github.com/milkymist/milkymist/blob/master/software/libbase/uart.c#L48" class="external free" title="https://github.com/milkymist/milkymist/blob/master/software/libbase/uart.c#L48" rel="nofollow">https://github.com/milkymist/milkymist/blob/master/software/libbase/uart.c#L48</a>
</p>
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