Networking:
- -It is possible to let the guest OS running inside the emulator get access to -the Internet. If you are interested in the technical details, and the -reasons why networking is implemented in the emulator the way it currently -is implemented, you might want to read the -networking section in the technical documentation. --The guest OS running inside the emulator uses a private IPv4 address, such -as 10.0.0.1, and the emulator acts as a NAT-like gateway/firewall at IPv4 -address 10.0.0.254. To the outside world it will seem like it is the host's -OS that connects to other machines on the internet, not the guest OS. -
-NOTE: This is still experimental! -As of 2004-07-21, ARP + ICMP + UDP + TCP are emulated well enough to let -NetBSD and OpenBSD install via ftp, and use the network for many normal -activities, but not everything works yet. - - +
Writing operating system code, or developing firmware, using GXemul:
+Is this a good idea? The answer is yes and no, depending on the level of +detail you need in your simulations. If you are developing an operating +system or operating system kernel of your own, then the emulator can be a +complement to testing on real hardware. -Porting operating systems to MIPS using GXemul:
+Important things to keep in mind: -Is this a good idea? The answer is yes and no, depending on what you are -trying to port to. If you are developing an operating system or operating -system kernel of your own, and wish to target MIPS-like systems in general, -then the answer might be yes, for experimental purposes. - -
-However, if you think that you can port an operating system -to, say, the Silicon Graphics machine mode of GXemul and hope that your -operating system will run on a real SGI machine, then you will most -likely fail. GXemul simply does not emulate things well enough for that to work. -Another example would be specific CPU details; if your code depends on, -say, R10000 specifics, chances are that GXemul will not be sufficient. - -
-In many cases, hardware devices in GXemul are only implemented well -enough to fool eg. NetBSD that they are working correctly, while in -fact they don't work very much at all. Please keep this in mind, if you plan -to use GXemul when porting your code to MIPS. +
-
+
- Porting code to a specific machine mode, e.g. a Silicon Graphics
+ machine, using GXemul, will not "magically" cause the code to
+ work on a real machine. Sometimes code works in GXemul which doesn't
+ work on real hardware, sometimes it's the other way around.
+
+
+
- GXemul contains bugs, and many things are not yet implemented.
+
+
+
- Very important! I have only implemented devices in GXemul
+ to the degree that NetBSD, OpenBSD, Linux, etc don't complain too much.
+
+ If you are developing a driver for a device which is emulated by + GXemul, and your driver does not seem to be working, then the + probability of a bug in GXemul's implementation of the device is + very much higher than that of a bug in your driver. +
+ The device implementations in GXemul are based on the assumption + that the emulated OS is already developed and bug-free. They are + not primarily intended to be used for development of new device + driver code in operating systems, so if you do that, then be + prepared for bugs and inconsitencies. +
+
- CPU details in GXemul are usually wrong. If your code depends
+ on, say, R10000 or MIPS64 specifics, chances are that GXemul will
+ not be sufficient. One example is different revisions of ISAs;
+ some instructions which should trigger an exception on a
+ real MIPS processor usually execute anyway in GXemul. Another
+ example is if userland code tries to access kernel memory; in some
+ cases there is protection against this, but not in all cases (to get
+ higher performance).
+
+
- Caches. There is no cache emulation in GXemul right now. Caches + for R2000/R3000 are faked well enough to run NetBSD, Ultrix, etc + in the DECstation emulation mode, but other than that, cache + operations are treated as nops. +
The bottom line is that GXemul can be useful as yet another way to test +your code during development, but it should not be fully relied on. @@ -123,16 +128,16 @@
Using GXemul in compiler contruction courses:
If you are learning how to write a compiler, and wish to target a -realistic target platform, then MIPS (as emulated by GXemul) -might be a suitable choice. +realistic target platform, then MIPS or ARM (as emulated by GXemul) +might be suitable choices.- (+) Your compiler needs to output real assembly
- language code, which the assembler (eg gas, the GNU assembler) can
+ language code, which the assembler (e.g. gas, the GNU assembler) can
then compile into object format, and then you need to link this
into an executable image. This is much closer to how things work
in real life than running assembly language listings in a simulator
- (eg SPIM).
+ (e.g. SPIM).
- (-) GXemul does not simulate out-of-order
execution, penalties related to instruction scheduling, or
@@ -158,37 +163,37 @@
Here are some examples. If you want to run a NetBSD/pmax kernel on an
emulated DECstation machine, you would use a command line such as this:
- $ gxemul -E dec -e 3max -b -d pmax_diskimage.fs netbsd-pmax-INSTALL + $ gxemul -e 3max -d pmax_diskimage.fs netbsd-pmax-INSTALL
--NOTE: For some emulation modes, such as the DECstation mode, you do -not have to specify the name of the kernel, if the disk image is -bootable! -
-It is possible to have more than one disk. For each -d argument, a disk + +
NOTE: For some emulation modes, such as the DECstation mode, you do +not actually have to specify the name of the kernel, if the disk +image is bootable! + +
It is possible to have more than one disk. For each -d argument, a disk image is added; the first will be SCSI target 0, the second will be target 1, and so on, unless you specify explicitly which ID number the devices should have.
- $ gxemul -E dec -e 3max -b -d disk0.raw -d disk1.raw -d 5:disk2.raw netbsd-pmax-INSTALL + $ gxemul -e 3max -d disk0.raw -d disk1.raw -d 5:disk2.raw netbsd-pmax-INSTALL
Note: In the example above, disk2.raw will get scsi id 5. --If a filename has a 'c' prefix, or ends with ".iso", then it is assumed to be + +
If a filename has a 'c' prefix, or ends with ".iso", then it is assumed to be a CDROM device (this can be overridden with a 'd' prefix, to force a read/write disk). For example, the following command would start the emulator with two CDROM images, and one harddisk image:
- $ gxemul -E dec -e 3max -b -d image.iso -d disk0.img -d c:second_cdrom.img netbsd-pmax-INSTALL + $ gxemul -e 3max -d image.iso -d disk0.img -d c:second_cdrom.img netbsd-pmax-INSTALL
Usually, the device with the lowest id becomes the boot device. To override this, add a 'b' prefix to one of the devices:- $ gxemul -E dec -e 3max -b -d rootdisk.img -d bc:install-cd.iso name_of_kernel + $ gxemul -e 3max -d rootdisk.img -d bc:install-cd.iso name_of_kernel
If you have a physical CD-ROM drive on the host machine, say /dev/cd0c, you can use it as a CD-ROM directly accessible from within the emulator:- $ gxemul -E dec -e 3max -b -d rootdisk.img -d bc:/dev/cd0c name_of_kernel + $ gxemul -e 3max -d rootdisk.img -d bc:/dev/cd0c name_of_kernel
It is probably possible to use harddisks as well this way, but I would not recommend it. @@ -244,6 +249,53 @@ + + + +Transfering files to/from the guest OS:
+ +If the emulated machine supports networking (see this section for more info), then +transfering files via FTP is probably easiest. + +There is another way of transfering files which works for any kind of +emulated machine which supports disks (either SCSI or IDE). Any file can +be supplied as a disk image. For example, consider the following:
+ $ gxemul -XEcats -d nbsd_cats.img -d archive.tar.gz netbsd-GENERIC +
+This will start NetBSD/cats with nbsd_cats.img as IDE master on +controller 0 (wd0), and archive.tar.gz as IDE slave on controller +0 (wd1). From inside NetBSD, it is now possible to extract the files using +the following command:+ (inside emulated NetBSD/cats) + # tar zxvf /dev/wd1c +
+Don't worry if NetBSD complains about lack of disklabel; it doesn't +matter. On some machines, NetBSD uses wd1d instead of +wd1c for the entire disk. +There is also a minor problem: reading the end of the disk image. If you +experience problems untaring archives like this, then pad out the archive +first with some zeroes. + +Transfering files out from the emulated operating system to the +host can be done the same way. First, prepare an empty archive file:
+ $ dd if=/dev/zero of=newarchive.tar bs=1024 count=1 seek=10000 +
This example created a 10 MB empty file. Then, start the emulator +like this:+ $ gxemul -XEcats -d nbsd_cats.img -d archive.tar netbsd-GENERIC +
+and transfer files by creating an archive directly onto the disk image:+ (inside emulated NetBSD/cats) + # tar cvf /dev/wd1c filenames +
+where filenames are the files or directories to transfer. + + + + +How to extract large gzipped disk images:
@@ -288,12 +340,14 @@Running userland binaries:
-You can run (some) userland programs as well. This will not emulate any -particular machine, but instead try to translate syscalls from for example -NetBSD/pmax into the host's OS' syscalls. Right now, this is just a -proof-of-concept, to show that it would work; there's lots of work left to -do to make it actually run useful programs (for example dynamically linked -programs). +Note: This feature does not really work yet. +It is currently disabled in stable release builds of the emulator. + +There is some skeleton code for running userland programs as well. This +will not emulate any particular machine, but instead try to translate +syscalls from e.g. NetBSD/pmax into the host's OS' syscalls. Right now, +this is just a proof-of-concept, to show that it could work; there's lots +of work left to do to make it actually run useful programs.
@@ -324,6 +378,7 @@ tab.csbnet.se +
- $ gxemul -E dec -e 3min -Q -M128 -q 0xbfc00000:DECstation5000_125_promdump.bin + $ gxemul -e 3min -Q -M128 -q 0xbfc00000:DECstation5000_125_promdump.bin KN02-BA V5.7e ?TFL: 3/scc/access (1:Ln1 reg-12: actual=0x00 xpctd=0x01) [KN02-BA] @@ -455,18 +511,20 @@ osconsole=3 >>-(Note: at the moment, this doesn't work. I must have broken something when -fixing something else, but this is what it looked like at the time.) -
-During bootup, the PROM complains a lot about hardware failures. + +
(Note: at the moment, this doesn't work. +I must have broken something when fixing something else, but this +is what it looked like at the time.) + +
During bootup, the PROM complains a lot about hardware failures. That's because the emulator doesn't emulate the hardware well enough yet. -
-The command line options used are: -E dec for DECstation, -e 3min for -"model 3" (5000/1xx), -Q to supress the emulator's own PROM -call emulation, -M128 for 128MB RAM (because GXemul doesn't correctly + +
The command line options used are: -e 3min for +"DECstation 3min" (5000/1xx), -Q to supress the emulator's own PROM +call emulation, -M128 for 128MB RAM (because GXemul doesn't correctly emulate memory detection well enough for the PROM to accept, so it will -always believe there is 128MB ram anyway), and -q to supress debug messages. -The 0xbfc00000 in front of the filename tells GXemul that it is a raw +always believe there is 128MB ram anyway), and -q to supress debug messages. +The 0xbfc00000 in front of the filename tells GXemul that it is a raw binary file which should be loaded at a specific virtual address. @@ -474,20 +532,53 @@
Dumping the PROM on a SGI O2:
The general ideas in this section applies to using ROM images from other -machines as well. Besides DECstation, I've also tried this on an SGI IP32 -("O2"). --For the O2, a suitable command to dump the prom memory range is +machines as well. I have also tried this on an SGI IP32 ("O2"), in addition +to the DECstation. + +
For the O2, a suitable command to dump the prom memory range is
>> dump -b 0xBFC00000:0xBFC80000Make sure you capture all the output (via serial console) into a file, -and then run experiments/sgiprom_to_bin on the captured file. -
-(2005-01-16: The emulator doesn't really emulate the IP32 well enough to -actually run the PROM image without using special hacks, but it might do -so some time in the future.) +and then run experiments/sgiprom_to_bin on the captured file. +
+
+
+
+
+
+
+
+
The photo on the left is from the real machine. The other two are +screenshots of the PROM running experimentally in GXemul, using -Y2 +framebuffer scaledown. + +
Normally during bootup, the IP32 PROM does a Power-On test which makes +sure that the caches and other things are working properly. GXemul doesn't +emulate all those things well enough for the tests to pass. The +experimental screenshots above were taken with cache detection skipped +manually. + +
+In other words: don't expect this to work out-of-the-box with GXemul right +now. It might work once I've added correct cache emulation. + +
The command line used to start the emulator, once correct cache +emulation has been implemented, would be something like gxemul -XQeo2 +0xbfc00000:prom.bin. + +
The same caution applies when dealing with SGI PROMs as with +DECstation PROMs: GXemul doesn't really emulate the hardware, it only +"fakes" devices well enough to fool some things, primarily NetBSD, that +it is emulating a real machine. ROM code is usually a lot more +picky about the details. + +
The graphics used in the O2 is (as far as I know) undocumented. Combining +some traces of info from how Linux/O2 draws to the screen with some +reverse-engineering of my own, I've implemented enough of the controller to +let the PROM draw rectangles and bitmaps, but not much more. The SCSI +controller is not implemented yet either.