Xilinx EDK 8.2i manual Interrupt and Exception Handling

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Chapter 3: MicroBlaze Application Binary Interface

Interrupt and Exception Handling

MicroBlaze assumes certain address locations for handling interrupts and exceptions as indicated in Table 3-3. At these locations, code is written to jump to the appropriate handlers.

Table 3-3:Interrupt and Exception Handling

On	Hardware jumps to	Software Labels
Start / Reset	0x0	_start
User exception	0x8	_exception_handler
Interrupt	0x10	_interrupt_handler
Break (HW/SW)	0x18	-
Hardware exception	0x20	_hw_exception_handler
Reserved by Xilinx for	0x28 - 0x4F	-
future use

The code expected at these locations is as shown in Figure 3-3. For programs compiled without the -xl-mode-xmdstubcompiler option, the crt0.o initialization file is passed by the mb-gcc compiler to the mb-ldlinker for linking. This file sets the appropriate addresses of the exception handlers.

For programs compiled with the -xl-mode-xmdstubcompiler option, the crt1.o initialization file is linked to the output program. This program has to be run with the xmdstub already loaded in the memory at address location 0x0. Hence at run-time, the initialization code in crt1.o writes the appropriate instructions to location 0x8 through 0x14 depending on the address of the exception and interrupt handlers.

Figure 3-3:Code for passing control to exception and interrupt handlers

0x00:	bri	_start1
0x04:	nop
0x08:	imm	high bits of address (user exception handler)
0x0c:	bri	_exception_handler
0x10:	imm	high bits of address (interrupt handler)
0x14:	bri	_interrupt_handler
0x20:	imm	high bits of address (HW exception handler)
0x24:	bri	_hw_exception_handler

MicroBlaze allows exception and interrupt handler routines to be located at any address location addressable using 32 bits. The user exception handler code starts with the label _exception_handler, the hardware exception handler starts with _hw_exception_handler, while the interrupt handler code starts with the label _interrupt_handler.

In the current MicroBlaze system, there are dummy routines for interrupt and exception handling, which you can change. In order to override these routines and link your interrupt and exception handlers, you must define the interrupt handler code with an attribute interrupt_handler. For more details about the use and syntax of the interrupt handler attribute, please refer to the GNU Compiler Tools chapter in the document: UG111 Embedded System Tools Reference Manual.

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