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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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