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An error handling routine may be set up by using the system OS_Erh whose specification is:
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| Code Block | ||||
|---|---|---|---|---|
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In:
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IN: A = 0, other values reserved for system use |
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B = 0 |
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HL = address of new error handler |
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HL = 0, use default system error handler (in lower 8K of segment 0) |
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OUT: |
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Fc = 0 |
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A = old call level |
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HL = address of old error handler |
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Registers changed after return: |
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...CDE../IXIY same |
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AFB...HL/.... different |
We can now consider the code the error handler should include. Fatal errors may be ignored (include a RET Z at the start), because there is no reasonable action to take anyway except termination of this instantiation of the application. An RC_SUSP error code will generally be completely ignored by the error handler whereas RC_ESC may want to be acknowledged using OS_Esc, or left pending for the main part of the application to acknowledge. RC_DRAW could be responded to by calling a routine to regenerate the screen and then quitting the error handler with A = RC_SUSP and Fc = 0 as though nothing had ever happended. Other errors may want to be reported, by outputting an error message.
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