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<H2><A NAME="s3">3. Interrupts (IRQs) and DMA access</A></H2>

<P>You cannot use IRQs or DMA directly from a user-mode process. You need
to write a kernel driver; see 
<A HREF="http://www.redhat.com:8080/HyperNews/get/khg.html">The Linux Kernel Hacker's Guide</A> for details and the kernel source code
for examples.
<P>You can disable interrupts from within a user-mode program, though it can
be dangerous (even kernel drivers do it for as short a time as possible).
After calling <CODE>iopl(3)</CODE>, you can disable interrupts simply by calling
<CODE>asm("cli");</CODE>, and re-enable them with <CODE>asm("sti");</CODE>.
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