Qemu is a generic open source processor and system emulator. It achieves good performance from using a Just-in-time compilation.
- 1 System architecture
- 2 Status
- 3 Patches
- 4 Common Problems
- 5 MIPS HOST SUPPORT
- 6 See also
- 7 Credits
This paragraph describes the architecture of the MIPS system that currently is being emulated by Qemu. As Qemu is still very much work in progress this is expected to change.
There currently is no firmware for Qemu. This is only a minor problem as unlike on a real system Qemu's virtual hardware is mostly initialized after a reset.
Qemu is emulating a simply machine with ISA-like bus. ISA IO space mapped to the 0x14000000 (PHYS) and ISA memory at the 0x10000000 (PHYS, 16Mb in size). All peripherial devices are attached to this "bus" with the standart PC ISA addresses.
Qemu is simulating a 4Kc MIPS32 processor with a 16 entry TLB. Both I-cache and D-cache are 4kB each, 2-way set-associative with 16 bytes per cacheline however the cache effects are not simulated and cacheops are treated as noops. This is a design decission to improve performance over accuracy. No benchmarking has been done however it is expected that the performance of the virtual MIPS system will be comparable to emulation of the other processors.
Qemu's source code can also be configured to be built with support for a 4Km processor. However being TLB-less this processor is not of interest for Linux, so does not currently receive any sort of attention.
Qemu is emulating the standard builtin interrrupt controller including soft interrupts and the count/compare interrupt of R4000-class processors. Cascaded externally to that is a i8259 PIC interrupt controller that is cascaded to the CPU's INT0.
Qemu is emulating a standard VGA graphics card however underlined, bold and blinking attributes are not supported.
Qemu is emulating a PC-style 8250-based serial interface.
Qemu is emulating a single ISA NE2000 network card.
Qemu supports other peripherals however support for them has not been integrated or tested into the MIPS port.
At this time the MIPS support still is in pre-alpha stage. There is no firmware for Qemu yet, and only the CVS HEAD version of Qemu can run a userland on top of a MIPS kernel.
MIPS support is integrated into Qemu (CVS HEAD, still experimental), and also in the Linux kernel.
Qemu currently doesn't emulate any existing MIPS system. The Linux kernel has a special configuration to support the Qemu platform, no additional patches are needed.
All MIPS Qemu patches have been integrated into the Qemu CVS.
MIPS BIOS not found on startup
[ralf@box qemu]$ qemu-system-mips -kernel /tftboot/192.168.0.1/vmlinux.bin -m 16 -nographic (qemu) mips_r4k_init: start mips_r4k_init: load BIOS '/usr/local/share/qemu/mips_bios.bin' size 131072 qemu: could not load MIPS bios '/usr/local/share/qemu/mips_bios.bin' [ralf@box qemu]$
There currently is no MIPS BIOS file for Qemu. However if passed a -kernel argument qemu will not call the firmware at all, so this does no harm at all. Therefore, a command such as
dd if=/dev/zero of=/usr/local/share/qemu/mips_bios.bin bs=1024 count=128
will generate a firmware file that will do the job for now.
MIPS HOST SUPPORT
In 2004, I successfully compiled QEMU on a SGI machine, using a patch found here:
I hope this patch could merge into the new qemu release. Thanks! -- Tinybit <tinybit at tom dot com>
- The Qemu homepage at http://fabrice.bellard.free.fr/qemu.
Originally authored by French wizzard Fabrice Bellard, Jocelyn Mayer did add support for MIPS as a target, others are now trying to complete the project.