| 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 3 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, see <http://www.gnu.org/licenses/>. |
| 17 | |
| 18 | */ |
| 19 | |
| 20 | |
| 21 | #ifndef _EMUL_CHIRP_H_ |
| 22 | #define _EMUL_CHIRP_H_ |
| 23 | |
| 24 | /* EMUL_CHIRP: |
| 25 | |
| 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. |
| 30 | |
| 31 | The OpenBoot client interface is implemented by using two |
| 32 | instructions: |
| 33 | |
| 34 | client_interface: |
| 35 | <emul_call> |
| 36 | blr |
| 37 | |
| 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. |
| 42 | |
| 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. |
| 48 | |
| 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. |
| 52 | |
| 53 | Handling this are the emul_chirp states: |
| 54 | |
| 55 | serving---. |
| 56 | / | |
| 57 | Emulation compleated ^ v Client makes call to |
| 58 | - restore int vectors | | emulated interface |
| 59 | ^ v - patch exception vectors |
| 60 | | / |
| 61 | `-emulating-. emulating the request |
| 62 | / | |
| 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 |
| 67 | - restart request | / |
| 68 | `--faulting |
| 69 | */ |
| 70 | |
| 71 | |
| 72 | extern const os_emul emul_chirp; |
| 73 | |
| 74 | #endif |