git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@549 35acf78f-673a-0410-8e92-d51de3d6d3f4

1 files changed, 26 insertions, 3 deletions

diff --git a/docs/ch.txt b/docs/ch.txt
index 4db76915a..46fd52004 100644
--- a/docs/ch.txt
+++ b/docs/ch.txt
@@ -159,11 +159,34 @@
  *     architecture.</li>

  * <li>FIQ sources can preempt the kernel (by design) so it is not possible to

  *     invoke the kernel APIs from inside a FIQ handler.</li>

+ * <li>Interrupt handlers do not save function-saved registers so you need to

+ *     make sure your code saves them or does not use them (this happens

+ *     because in the ARM7 port all the OS interrupt handlers are declared

+ *     naked).<br>

+ *     Function-trashed registers (R0-R3,R12,LR,SR) are saved/restored by the

+ *     system macros \p chSysIRQEnterI() and \p chSysIRQExitI().<br>

+ *     The easiest way to ensure this is to just invoke a function from within

+ *     the interrupt handler, the function code will save all the required

+ *     registers.<br>

+ *     Example:

+ * @code

+ * __attribute__((naked, weak))

+ * void irq_handler(void) {

+ *   chSysIRQEnterI();

+ *

+ *   serve_interrupt();

+ *

+ *   VICVectAddr = 0; // This is LPC214x-specific.

+ *   chSysIRQExitI();

+ * }

+ * @endcode

+ *     This is not a bug but an implementation choice, this solution allows to

+ *     have interrupt handlers compiled in thumb mode without have to use an

+ *     interworking mode (the mode switch is hidden in the macros), this

+ *     greatly improves code efficiency and size. You can look at the serial

+ *     driver for real examples of interrupt handlers.</li>

  * </ul>

  * </p>

- * <p>

- * The ARM7 port is shared by multiple demos targeted to various implementations:

- * </p>

  * @ingroup Ports

  */

 /** @} */