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<html><head><title>Gavare's eXperimental Emulator: Experimenting with GXemul</title> |
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<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6"> |
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<b>Gavare's eXperimental Emulator:</b></font><br> |
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<font color="#000000" size="6"><b>Experimenting with GXemul</b> |
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</font></td></tr></table></td></tr></table><p> |
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|
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$Id: experiments.html,v 1.96 2006/02/18 13:15:20 debug Exp $ |
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Copyright (C) 2003-2006 Anders Gavare. All rights reserved. |
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Redistribution and use in source and binary forms, with or without |
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--> |
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<a href="./">Back to the index</a> |
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|
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<p><br> |
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<h2>Experimenting with GXemul</h2> |
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|
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<p> |
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<ul> |
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<li><a href="#hello">Hello world</a> |
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<li><a href="#expdevices">Experimental devices</a> |
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</ul> |
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|
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|
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|
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|
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|
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|
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<p><br> |
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<a name="hello"></a> |
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<h3>Hello world:</h3> |
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|
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You might want to use the emulator to develop programs on your own, |
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not just run precompiled kernels such as NetBSD. To get started, I recommend |
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that you do two things: |
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|
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<p> |
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<ul> |
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<li>Build and install a cross-compiler for MIPS. |
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<li>Compile this hello world program, and run it in the emulator. |
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</ul> |
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|
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<p> |
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<table border="0"><tr><td width="40"> </td><td> |
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<pre> |
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<font color=#f00000>/* Hello world for GXemul */ |
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|
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/* Note: The cast to a signed int causes the address to be sign-extended |
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correctly to 0xffffffffb00000xx when compiled in 64-bit mode */ |
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</font><font color=#a0a0a0>#define PUTCHAR_ADDRESS ((signed int)0xb0000000) |
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#define HALT_ADDRESS ((signed int)0xb0000010) |
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|
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</font><font color=#c000c0>void </font><font color=#000000><a name="printchar">printchar</a>(</font><font color=#c000c0>char </font><font color=#000000>ch) |
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{ |
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*((</font><font color=#c000c0>volatile unsigned char </font><font color=#000000>*) PUTCHAR_ADDRESS) = ch; |
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} |
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|
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</font><font color=#c000c0>void </font><font color=#000000><a name="halt">halt</a>(</font><font color=#c000c0>void</font><font color=#000000>) |
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{ |
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*((</font><font color=#c000c0>volatile unsigned char </font><font color=#000000>*) HALT_ADDRESS) = 0; |
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} |
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|
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</font><font color=#c000c0>void </font><font color=#000000><a name="printstr">printstr</a>(</font><font color=#c000c0>char </font><font color=#000000>*s) |
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{ |
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</font><font color=#c000c0>while </font><font color=#000000>(*s) |
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printchar(*s++); |
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} |
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|
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</font><font color=#c000c0>void </font><font color=#000000>f(</font><font color=#c000c0>void</font><font color=#000000>) |
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{ |
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printstr(</font><font color=#00c000>"Hello world\n"</font><font color=#000000>); |
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halt(); |
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} |
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</font></pre> |
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</td></tr></table> |
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|
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<p>(This hello world program is available here as well: |
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<a href="hello_mips.c"><tt>hello_mips.c</tt></a>) |
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|
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<p>I recommend that you build a GCC cross compiler for the |
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<b>mips64-unknown-elf</b> target, and install it. Other compilers could |
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work too, but GCC is good because of its portability. Then try to compile |
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and link the hello world program: |
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<pre> |
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$ <b>mips64-unknown-elf-gcc -O2 hello_mips.c -mips4 -mabi=64 -c</b> |
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$ <b>mips64-unknown-elf-ld -Ttext 0xa800000000030000 -e f hello_mips.o -o hello_mips --oformat=elf64-bigmips</b> |
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$ <b>file hello_mips</b> |
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hello_mips: ELF 64-bit MSB mips-4 executable, MIPS R3000_BE, version 1 (SYSV), statically linked, not stripped |
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$ <b>gxemul -q -E testmips hello_mips</b> |
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Hello world |
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|
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$ <b>mips64-unknown-elf-gcc -O2 hello_mips.c -c</b> |
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$ <b>mips64-unknown-elf-ld -Ttext 0x80030000 -e f hello_mips.o -o hello_mips</b> |
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$ <b>file hello_mips</b> |
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hello_mips: ELF 32-bit MSB mips-3 executable, MIPS R3000_BE, version 1 (SYSV), statically linked, not stripped |
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$ <b>gxemul -q -E testmips hello_mips</b> |
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Hello world |
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</pre> |
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|
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<p> |
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As you can see above, a GCC configured for mips64-unknown-elf can produce |
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both 64-bit and 32-bit binaries. If you don't want to run the entire |
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Hello World program, but want to single-step through the execution to |
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learn more about how MIPS programs run, then add -V to the command line: |
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|
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<p> |
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<pre> |
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$ <b>gxemul -V -E testmips hello_mips</b> |
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.. |
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GXemul> <b>r</b> |
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cpu0: pc = a800000000030078 <f> |
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cpu0: hi = 0000000000000000 lo = 0000000000000000 |
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cpu0: zr = 0000000000000000 at = 0000000000000000 |
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cpu0: v0 = 0000000000000000 v1 = 0000000000000000 |
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.. |
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cpu0: gp = a8000000000780c0 sp = ffffffffa0007f00 |
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cpu0: fp = 0000000000000000 ra = 0000000000000000 |
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GXemul> <b>s 15</b> |
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<f> |
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a800000000030078: 67bdfff0 daddiu sp,sp,-16 |
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a80000000003007c: 3c04a800 lui a0,0xa800 |
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a800000000030080: 3c010003 lui at,0x3 |
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a800000000030084: 64840000 daddiu a0,a0,0 |
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a800000000030088: 642100b8 daddiu at,at,184 |
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a80000000003008c: 0004203c dsll32 a0,a0,0 |
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a800000000030090: 0081202d daddu a0,a0,at |
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a800000000030094: ffbf0000 sd ra,0(sp) [0xffffffffa0007ef0, data=0x0000000000000000] |
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a800000000030098: 0c00c00a jal 0xa800000000030028 <printstr> |
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a80000000003009c: 00000000 (d) nop |
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<printstr("Hello world\n",0,0,0,..)> |
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<printstr> |
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a800000000030028: 67bdfff0 daddiu sp,sp,-16 |
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a80000000003002c: ffb00000 sd s0,0(sp) [0xffffffffa0007ee0, data=0x0000000000000000] |
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a800000000030030: ffbf0008 sd ra,8(sp) [0xffffffffa0007ee8, data=0xa8000000000300a0] |
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a800000000030034: 90820000 lbu v0,0(a0) [0xa8000000000300b8 = $LC0, data=0x48] |
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a800000000030038: 00021600 sll v0,v0,24 |
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GXemul> <b>print v0</b> |
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v0 = 0x0000000048000000 |
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GXemul> <b>_</b> |
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</pre> |
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|
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<p>The syntax of the single-step debugger shouldn't be too hard to grasp. |
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Type "<tt>s</tt>" to single-step one instruction. For some commands (e.g. |
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the single-step command), just pressing enter on a blank line will cause |
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the last command to be repeated. Type "<tt>quit</tt>" to quit. |
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|
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<p> |
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Hopefully this is enough to get you inspired. :-) |
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|
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|
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|
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|
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|
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|
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<p><br> |
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<a name="expdevices"></a> |
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<h3>Experimental devices:</h3> |
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|
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The emulator has several modes where it doesn't emulate any real machine. |
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It can either run in "bare" mode, where no devices are included by default |
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(just the CPU), or in a "test" mode where some simple devices are |
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emulated. |
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|
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<p>The test machines (<tt>testmips</tt>, <tt>testppc</tt>, etc) have the |
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following experimental devices: |
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|
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<p> |
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<center><table border="0" width="80%"> |
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|
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<tr> |
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<td align="left" valign="top" width="200"> |
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<a name="expdevices_cons"><b><tt>cons</tt>:</b></a> |
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<p>A simple console device, for writing |
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characters to the controlling terminal |
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and receiving keypresses. |
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<p>Source code: <font color="#0000f0"><tt>src/devices/dev_cons.c</tt></font> |
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<br>Default physical address:  <font color="#0000f0">0x10000000</font> |
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</td> |
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<td align="left" valign="top" width="25"> </td> |
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<td align="left" valign="top"> |
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<table border="0"> |
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<tr> |
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<td align="left" valign="top"><i><u>Offset:</u></i> </td> |
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<td align="left" valign="top"><i><u>Effect:</u></i></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x00</tt></td> |
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<td align="left" valign="top"> |
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Read: <b><tt>getchar()</tt></b> (non-blocking; returns |
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<tt>0</tt> if no char was available)<br> |
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Write: <b><tt>putchar(ch)</tt></b></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x10</tt></td> |
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<td align="left" valign="top">Read or write: <b><tt>halt()</tt></b><br> |
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(Useful for exiting the emulator.)</td> |
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</tr> |
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</table> |
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</td> |
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</tr> |
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|
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<tr height="15"> |
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<td height="15"> </td> |
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</tr> |
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|
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<tr> |
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<td align="left" valign="top"> |
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<a name="expdevices_mp"><b><tt>mp</tt>:</b></a> |
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<p>This device controls the behaviour of CPUs in an emulated |
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multi-processor system. |
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<p>Source code: <font color="#0000f0"><tt>src/devices/dev_mp.c</tt></font> |
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<br>Default physical address:  <font color="#0000f0">0x11000000</font> |
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</td> |
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<td></td> |
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<td align="left" valign="top"> |
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<table border="0"> |
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<tr> |
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<td align="left" valign="top"><i><u>Offset:</u></i> </td> |
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<td align="left" valign="top"><i><u>Effect:</u></i></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0000</tt></td> |
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<td align="left" valign="top">Read: <b><tt>whoami()</tt></b>. |
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Returns the id of the CPU doing the read.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0010</tt></td> |
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<td align="left" valign="top">Read: <b><tt>ncpus()</tt></b>. |
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Returns the number of CPUs in the system.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0020</tt></td> |
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<td align="left" valign="top">Write: <b><tt>startupcpu(i)</tt></b>. |
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Starts CPU i. It begins execution at the address |
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set by a write to startupaddr (see below).</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0030</tt></td> |
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<td align="left" valign="top">Write: <b><tt>startupaddr(addr)</tt></b>. |
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Sets the starting address for CPUs.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0040</tt></td> |
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<td align="left" valign="top">Write: <b><tt>pause_addr(addr)</tt></b>. |
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Sets the pause address. (TODO: This is not |
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used anymore?)</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0050</tt></td> |
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<td align="left" valign="top">Write: <b><tt>pause_cpu(i)</tt></b>. |
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Stops all CPUs <i>except</i> CPU i.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0060</tt></td> |
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<td align="left" valign="top">Write: <b><tt>unpause_cpu(i)</tt></b>. |
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Unpauses all CPUs <i>except</i> CPU i.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0070</tt></td> |
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<td align="left" valign="top">Write: <b><tt>startupstack(addr)</tt></b>. |
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Sets the startup stack address. (CPUs started with |
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startupcpu() above will have their stack pointer |
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set to this value.)</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0080</tt></td> |
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<td align="left" valign="top">Read: <b><tt>hardware_random()</tt></b>. |
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This produces a "random" number.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0090</tt></td> |
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<td align="left" valign="top">Read: <b><tt>memory()</tt></b>. |
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Returns the number of bytes of RAM in the system.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x00a0</tt></td> |
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<td align="left" valign="top">Write: <b><tt>ipi_one((nr << 16) + cpuid)</tt></b>. |
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Sends IPI <tt>nr</tt> to a specific CPU.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x00b0</tt></td> |
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<td align="left" valign="top">Write: <b><tt>ipi_many((nr << 16) + cpuid)</tt></b>. |
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Sends IPI <tt>nr</tt> to all CPUs <i>except</i> |
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the specified one.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top">0x00c0</tt></td> |
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<td align="left" valign="top">Read: <b><tt>ipi_read()</tt></b>. |
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Returns the next pending IPI. 0 is returned if there is no |
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pending IPI (so 0 shouldn't be used for valid IPIs). |
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Hardware int 6 is deasserted when the IPI queue is empty. |
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<br>Write: <b><tt>ipi_flush()</tt></b>. |
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Clears the IPI queue, discarding any pending IPIs.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top">0x00d0</tt></td> |
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<td align="left" valign="top">Read: <b><tt>ncycles()</tt></b>. |
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Returns approximately the number of cycles executed. |
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Note: this value is not updated for every instruction, |
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so it cannot be used for small measurements.</td> |
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</tr> |
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</table> |
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</td> |
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</tr> |
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|
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<tr height="15"> |
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<td height="15"> </td> |
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</tr> |
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|
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<tr> |
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<td align="left" valign="top"> |
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<a name="expdevices_fb"><b><tt>fb</tt>:</b></a> |
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<p>A simple linear framebuffer, for graphics output. |
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640 x 480 pixels, 3 bytes per pixel (red, green, blue, 8 bits each). |
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<p>Source code: <font color="#0000f0"><tt>src/devices/dev_fb.c</tt></font> |
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<br>Default physical address:  <font color="#0000f0">0x12000000</font> |
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</td> |
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<td></td> |
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<td align="left" valign="top"> |
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<table border="0"> |
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<tr> |
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<td align="left" valign="top"><i><u>Offset:</u></i> </td> |
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<td align="left" valign="top"><i><u>Effect:</u></i></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x00000-</tt><br><tt>0xe0fff</tt></td> |
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<td align="left" valign="top">Read: read pixel values. |
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<br>Write: write pixel values.</td> |
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</tr> |
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</table> |
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</td> |
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</tr> |
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|
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<tr height="15"> |
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<td height="15"> </td> |
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</tr> |
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|
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<tr> |
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<td align="left" valign="top"> |
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<a name="expdevices_disk"><b><tt>disk</tt>:</b></a> |
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<p>Disk controller, which can read from and write |
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to disk images. It does not use interrupts; read and |
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write operations finish instantaneously. |
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<p>Source code: <font color="#0000f0"><tt>src/devices/dev_disk.c</tt></font> |
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<br>Default physical address:  <font color="#0000f0">0x13000000</font> |
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</td> |
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<td></td> |
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<td align="left" valign="top"> |
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<table border="0"> |
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<tr> |
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<td align="left" valign="top"><i><u>Offset:</u></i> </td> |
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<td align="left" valign="top"><i><u>Effect:</u></i></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0000</tt></td> |
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<td align="left" valign="top">Write: Set the offset (in bytes) from the beginning |
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of the disk image. This offset will be used for the next read/write operation.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0010</tt></td> |
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<td align="left" valign="top">Write: Select the SCSI ID to be used in the next |
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read/write operation.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0020</tt></td> |
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<td align="left" valign="top">Write: Start a read or write operation. |
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(Writing <tt>0</tt> means a Read operation, a <tt>1</tt> means a |
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Write operation.)</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0030</tt></td> |
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<td align="left" valign="top">Read: Get status of the last operation. |
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(Status 0 means failure, non-zero means success.)</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x4000-</tt><br><tt>0x41ff</tt> </td> |
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<td align="left" valign="top">Read/Write: 512 bytes data buffer.</td> |
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</tr> |
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</table> |
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</td> |
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</tr> |
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|
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<tr height="15"> |
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<td height="15"> </td> |
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</tr> |
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|
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<tr> |
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<td align="left" valign="top"> |
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<a name="expdevices_ether"><b><tt>ether</tt>:</b></a> |
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<p>A simple ethernet controller, enough to send |
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and receive packets on a simulated network. |
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<p>Source code: <font color="#0000f0"><tt>src/devices/dev_ether.c</tt></font> |
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<br>Default physical address:  <font color="#0000f0">0x14000000</font> |
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</td> |
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<td></td> |
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<td align="left" valign="top"> |
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<table border="0"> |
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<tr> |
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<td align="left" valign="top"><i><u>Offset:</u></i> </td> |
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<td align="left" valign="top"><i><u>Effect:</u></i></td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x0000-</tt><br><tt>0x3fff</tt></td> |
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<td align="left" valign="top">Read/write buffer for the packet to be sent/received.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x4000</tt></td> |
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<td align="left" valign="top">Read: status word, one or more of these: |
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<br><tt>0x01</tt> = something was received (because of |
| 439 |
the last command) |
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<br><tt>0x02</tt> = more packets are available |
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<br><i>NOTE:</i> Whenever the status word is non-zero, |
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an interrupt is asserted. Reading the status word |
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clears it, and deasserts the interrupt.</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x4010</tt></td> |
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<td align="left" valign="top">Read: get the Length of the received packet |
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<br>Write: set the Length of the next packet to transmit</td> |
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</tr> |
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<tr> |
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<td align="left" valign="top"><tt>0x4020</tt></td> |
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<td align="left" valign="top">Write: command: |
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<br><tt>0x00:</tt> receive a packet |
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<br><tt>0x01:</tt> send a packet</td> |
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</tr> |
| 456 |
</table> |
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</td> |
| 458 |
</tr> |
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|
| 460 |
</table></center> |
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|
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<p> |
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While these devices may resemble real-world hardware, they are |
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intentionally made simpler to use. (An exception is the framebuffer; |
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some machines actually have simple linear framebuffers like this.) |
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|
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<p>If the physical address is <tt>0x10000000</tt>, then for MIPS that |
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means that it can be accessed at virtual address |
| 469 |
<tt>0xffffffffb0000000</tt>. (Actually it can be accessed at |
| 470 |
<tt>0xffffffff90000000</tt> too, but devices should usually be accessed in |
| 471 |
a non-cached manner.) |
| 472 |
|
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<p> (When using the PPC test machine (<tt>testppc</tt>), the addresses are |
| 474 |
<tt>0x10000000</tt>, <tt>0x11000000</tt> etc., so no need to add any |
| 475 |
virtual displacement.) |
| 476 |
|
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<p>The <b><tt>mp</tt></b>, <b><tt>disk</tt></b>, and <b><tt>ether</tt></b> |
| 478 |
devices are agnostic when it comes to word-length. For example, when |
| 479 |
reading offset <tt>0x0000</tt> of the <b><tt>mp</tt></b> |
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device, you may use any kind of read (an 8-bit read will work just as well |
| 481 |
as a 64-bit read, although the value will be truncated to 8 bits in the |
| 482 |
first case). You can <i>not</i>, however, read one byte from <tt>0x0000</tt> |
| 483 |
and one from <tt>0x0001</tt>, and combine the result. The read from |
| 484 |
<tt>0x0001</tt> will be invalid. |
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|
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<p>The <b><tt>cons</tt></b> device should be accessed using 8-bit reads |
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and writes. Doing a getchar() (ie reading from offset <tt>0x00</tt>) |
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returns <tt>0</tt> if no character was available. |
| 489 |
|
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<p>On MIPS, the <b><tt>cons</tt></b> device is hardwired to interrupt 2 |
| 491 |
(the lowest hardware interrupt). Whenever a character is available, the |
| 492 |
interrupt is asserted. When there are no more available characters, the |
| 493 |
interrupt is deasserted. (Remember that the interrupt has to be enabled in |
| 494 |
the status register of the system coprocessor.) |
| 495 |
|
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<p>The <b><tt>ether</tt></b> device is hardwired to interrupt 3. |
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|
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<p>The IPIs controlled by the <b><tt>mp</tt></b> device are hardwired to |
| 499 |
interrupt 6. Whenever an IPI is "sent", interrupt 6 is asserted on the |
| 500 |
target CPU(s), and the IPI number is added last in the IPI queue for that |
| 501 |
CPU. It is then up to that CPU to read from offset <tt>0x00c0</tt>, to |
| 502 |
figure out what kind of IPI it was. |
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|
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<p>A simple tutorial on how to use the <tt>disk</tt> device, if not clear |
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from the description above, can be found here: <a |
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href="test_disk.c"><tt>test_disk.c</tt></a> |
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|
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|
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|
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|
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</p> |
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|
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</body> |
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</html> |
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