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[/] [openrisc/] [trunk/] [gnu-old/] [gdb-6.8/] [sim/] [ppc/] [emul_chirp.h] - Blame information for rev 840

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1 24 jeremybenn
/*  This file is part of the program psim.
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    Copyright (C) 1994-1997, Andrew Cagney <cagney@highland.com.au>
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    This program is free software; you can redistribute it and/or modify
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    it under the terms of the GNU General Public License as published by
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    the Free Software Foundation; either version 2 of the License, or
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    (at your option) any later version.
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    This program is distributed in the hope that it will be useful,
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    but WITHOUT ANY WARRANTY; without even the implied warranty of
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    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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    GNU General Public License for more details.
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    You should have received a copy of the GNU General Public License
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    along with this program; if not, write to the Free Software
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    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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    */
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#ifndef _EMUL_CHIRP_H_
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#define _EMUL_CHIRP_H_
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/* EMUL_CHIRP:
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   The emulation of the OpenBoot client interface (as defined in 1275)
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   illustrates how it is possible for PSIM to implement an interface
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   that is both running in virtual memory and is called using a
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   standard function call interface.
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   The OpenBoot client interface is implemented by using two
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   instructions:
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        client_interface:
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                <emul_call>
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                blr
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   A client program makes a function call to `client_interface' using
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   the `bl' instruction.  The simulator will then execute the
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   <emul_call> instruction (which calls emul_chirp) and then the `blr'
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   which will return to the caller.
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   In addition to providing the `client_interface' entry point, while
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   a client request is being handled, emul_chirp patches (well it will
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   one day) the data access exception vector with a <emul_call>
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   instruction.  By doing this, emul_chirp is able to catch and handle
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   any invalid data accesses it makes while emulating a client call.
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   When such an exception occures, emul_chirp is able to recover by
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   restoring the processor and then calling the clients callback
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   interface so that the client can recover from the data exception.
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   Handling this are the emul_chirp states:
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                              serving---.
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                             /          |
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   Emulation compleated     ^           v Client makes call to
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     - restore int vectors  |           | emulated interface
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                            ^           v   - patch exception vectors
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                            |          /
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                            `-emulating-. emulating the request
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                             /          |
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                            |           v Emulation encounters
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   Client callback recovers ^           | data access exception
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   from data exception and  |           v   - re-enable vm
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   returns.                 ^           |   - call client callback
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     - restart request      |          /
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                            `--faulting
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   */
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extern const os_emul emul_chirp;
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#endif

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