3.10

Testing and Debugging SMM Code

An SMI routine can be debugged with standard debugging tools (such as DOS DEBUG) if the

following requirements are met:

1. The debugger will only be able to set a code break point using INT 3 outside of the SMI han-

dler. The debug control register DR7 is set to the reset value upon entry to the SMI handler.

Therefore, any break conditions in DR0-3 will be disabled after entry to SMM. Debug regis-

ters can be used if set after entry to the SMI handler and DR0-3 are saved.

2. The debugger needs to be running in real mode and the SMM routine can not enter protected

mode. This insures that normal system interrupts, BIOS calls and the debugger will work

correctly from SMM mode.

3. Before an INT 3 break point is executed, all segment registers should have their limits modi-

fied to 64K, or larger, within the SMM routine.

ST486DX - SMM SOFTWARE CONSIDERATIONS

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