1 /* This file is part of the program psim.
3 Copyright (C) 1994-1997, Andrew Cagney <cagney@highland.com.au>
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, see <http://www.gnu.org/licenses/>.
21 #ifndef _EMUL_CHIRP_H_
22 #define _EMUL_CHIRP_H_
26 The emulation of the OpenBoot client interface (as defined in 1275)
27 illustrates how it is possible for PSIM to implement an interface
28 that is both running in virtual memory and is called using a
29 standard function call interface.
31 The OpenBoot client interface is implemented by using two
38 A client program makes a function call to `client_interface' using
39 the `bl' instruction. The simulator will then execute the
40 <emul_call> instruction (which calls emul_chirp) and then the `blr'
41 which will return to the caller.
43 In addition to providing the `client_interface' entry point, while
44 a client request is being handled, emul_chirp patches (well it will
45 one day) the data access exception vector with a <emul_call>
46 instruction. By doing this, emul_chirp is able to catch and handle
47 any invalid data accesses it makes while emulating a client call.
49 When such an exception occures, emul_chirp is able to recover by
50 restoring the processor and then calling the clients callback
51 interface so that the client can recover from the data exception.
53 Handling this are the emul_chirp states:
57 Emulation compleated ^ v Client makes call to
58 - restore int vectors | | emulated interface
59 ^ v - patch exception vectors
61 `-emulating-. emulating the request
63 | v Emulation encounters
64 Client callback recovers ^ | data access exception
65 from data exception and | v - re-enable vm
66 returns. ^ | - call client callback
72 extern const os_emul emul_chirp
;
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