1 /* This file is part of the program psim. 2 3 Copyright (C) 1994-1997, Andrew Cagney <cagney@highland.com.au> 4 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 2 of the License, or 8 (at your option) any later version. 9 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. 14 15 You should have received a copy of the GNU General Public License 16 along with this program; if not, write to the Free Software 17 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 18 19 */ 20 21 22 #ifndef _EMUL_CHIRP_H_ 23 #define _EMUL_CHIRP_H_ 24 25 /* EMUL_CHIRP: 26 27 The emulation of the OpenBoot client interface (as defined in 1275) 28 illustrates how it is possible for PSIM to implement an interface 29 that is both running in virtual memory and is called using a 30 standard function call interface. 31 32 The OpenBoot client interface is implemented by using two 33 instructions: 34 35 client_interface: 36 <emul_call> 37 blr 38 39 A client program makes a function call to `client_interface' using 40 the `bl' instruction. The simulator will then execute the 41 <emul_call> instruction (which calls emul_chirp) and then the `blr' 42 which will return to the caller. 43 44 In addition to providing the `client_interface' entry point, while 45 a client request is being handled, emul_chirp patches (well it will 46 one day) the data access exception vector with a <emul_call> 47 instruction. By doing this, emul_chirp is able to catch and handle 48 any invalid data accesses it makes while emulating a client call. 49 50 When such an exception occures, emul_chirp is able to recover by 51 restoring the processor and then calling the clients callback 52 interface so that the client can recover from the data exception. 53 54 Handling this are the emul_chirp states: 55 56 serving---. 57 / | 58 Emulation compleated ^ v Client makes call to 59 - restore int vectors | | emulated interface 60 ^ v - patch exception vectors 61 | / 62 `-emulating-. emulating the request 63 / | 64 | v Emulation encounters 65 Client callback recovers ^ | data access exception 66 from data exception and | v - re-enable vm 67 returns. ^ | - call client callback 68 - restart request | / 69 `--faulting 70 */ 71 72 73 extern const os_emul emul_chirp; 74 75 #endif 76