Exception and Interrupt Handling - Revision history

Michael: Interrupt handler moved to Exception and Interrupt Handling

2008-05-27T18:51:57Z

Interrupt handler moved to Exception and Interrupt Handling

Michael: Whoops, the code corrected me

2007-09-18T18:30:33Z

Whoops, the code corrected me

Michael: Brief description of the interrupt handler

2007-09-18T17:48:29Z

Brief description of the interrupt handler

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Embedded XINU utilizes a interrupt handling system which allows components to register custom interrupt handlers to the system at runtime or use the default trap handler.

Since interrupt handling code can occupy at most 0x20 bytes of memory in the reserved system area, the interrupt handler must be efficient and robust. When an exception occurs the handler checks the cause register for the number of the exception, loads the known offset to the interrupt vector table (0x8000 0200) and adds the exception number to that offset. After the address of the exception handler is known, it is loaded into a register, checks if it is the NULL pointer (not set) and jumps to the handler code. If the handler is set to NULL, the code uses the default trap handler instead.

Interrupt handling occurs in a similar fashion, but relies on saving the state of the system which cannot occur in the simple interrupt handler.

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-Embedded XINU utilizes a interrupt handling system which allows components to register custom interrupt handlers to the system at runtime or use the default trap handler.
+[[Embedded XINU]] utilizes a interrupt handling system which allows components to register custom interrupt handlers to the system at runtime or fall-back to the default trap handler.
-Since interrupt handling code can occupy at most 0x20 bytes of memory in the reserved system area, the interrupt handler must be efficient and robust.  When an exception occurs the handler checks the cause register for the number of the exception, loads the known offset to the interrupt vector table (0x8000 0200) and adds the exception number to that offset.  After the address of the exception handler is known, it is loaded into a register, checks if it is the NULL pointer (not set) and jumps to the handler code.  If the handler is set to NULL, the code uses the default trap handler instead.
+MIPS processors will jump to and execute code beginning at <tt>0x8000 0180</tt> when an exception or interrupt occurs.  Code for handling traps must occupy no more than 0x20 bytes at this location (eight instructions), therefore Embedded XINU uses three instructions to jump to different code which will handle traps more robustly.
-Interrupt handling occurs in a similar fashion, but relies on saving the state of the system which cannot occur in the simple interrupt handler.
+In order to handle exceptions (such as TLB misses) efficiently, Embedded XINU uses an interrupt vector system to quickly read the exception code, load the registered exception handler, and jump to the handler.  If any of these steps do not exist, the handler will fall-back to the default trap handler.

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