Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!cs.utexas.edu!uunet!mcvax!unido!sbsvax!roeder
From: roeder@sbsvax.UUCP (Edgar Roeder)
Newsgroups: comp.sys.atari.st
Subject: Re: Critical error handler
Message-ID: <757@sbsvax.UUCP>
Date: 31 May 89 18:24:30 GMT
References: <26@meadow.UUCP>
Organization: Universitaet des Saarlandes, Saarbruecken, W-Germany
Lines: 35

In article <26@meadow.UUCP>, bill@meadow.UUCP (Bill Foster) writes:
> 
> Is this the critical error handler vector (etv_critic = 0x404)?  If I call

Yes it is.

>    What is the format and return values for the critical error handler
> routine?

The routine is called with 2 arguments:
	- the bios error number of the event causing the handler to be called
	- the drive which caused this error

The return value should be one of:
	      0L	- ignore the error
	0x10000L	- retry (possibly this gives the same error again)
	any other value	- return with this value as error (i.e. ABORT)
You can install a normal C-routine as the error handler. But you can only
call Bios-functions for terminal output, since the handler may be called
from a GEMDOS-function and since GEMDOS is not reentrant (*), you can't use
GEMDOS-functions like Cconout() (and most printf()'s in C-Compilers).
Also make sure that your C-compiler has a reentrant bios() binding - this
means that it uses a stack for the return-code from the bios()-function and
eventually saved registers and not a static storage location. Otherwise you
would have to use inline-assembler (like in MEGAMAX C, Laser C or GNU-C) or
a seperate assembler routine to call trap #13.

Hope this helps.

- Edgar

(*) GEMDOS is not reentrant when called by the Bios because it uses a static
(and undocumented (!)) storage location for the return address when it calls a
Bios-function like for example Rwabs() from inside Fwrite() which eventually
calls the critical error handler.