I've been looking at QEMU for a while now and I've been trying to find out if I can use it to simulate a device that we are developing.
The device will be powered by an ARM Cortex M3 and QEMU is well suited for emulation of its software.
What I want to know is if anyone has used QEMU in the past as a simulator?
The intent is to use QEMU to do black-box testing of the software before rolling it out to the devices in the field.
This would involve being able to monitor and modify the memory location in which your Parallel Input/Output (PIO) pins are configured and set and the memory locations of all other peripherals externally.
Now, considering that some of the peripherals would be PWM and UART, it is clear that there will be a need to resolve synchronization issues. However, I would like to avoid this topic for the time being and stick only to simple PIO.
The QEMU Monitor gets close but is not quite there yet.
So to summarize:
I need to know if there is a way to interrupt QEMU after each CPU clock cycle and read/write to a small number of memory locations in the code memory.
Did you try to use GDB stub ? You can use -s -S and connect through gdb by target remote :1234. This will give you control over program executed inside vm and access to registers and memory.
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I have and issue that the only way the FPGA on a myRIO Module runs is if it is programmed over USB. It does not run after powering down and back up. It does run after unplugging the laptop after it has been programmed over USB. I suspect that not running after a power cycle is because the FPGA is only getting the image loaded internally over USB.
Is there some special LabVIEW command to program the serial flash on the FPGA so that the FPGA runs at powerup, or does programming the FPGA over USB always program the serial Flash?
Do you have just FPGA part, and no Real-Time application? In case of just FPGA part, it is enough to build bitfile, and then deploy it (actually, upload it to myRIO and set to run at boot). Here is Knowledgebase article from NI about how to achieve it.
In case when you also have Real-Time part, then it should be also deployed, and set to run at the boot. Here is another detailed article about how to configure it: Deploy a Startup Application to Your MyRIO.
During development with Wind River Workbench, I use VxWorks Simulator to test code. I also heard of Simics is a virtual environment which can run VxWorks. Are Simics and VxWorks Simulator the same thing?
They are 2 different products.
VxSim is bundled with the vxWorks development environment and provides a simple x86 virtual board with memory, a serial port and possibly a network connection. You can not simulate real devices like A/D, PCI devices, etc... in vxSim
Simics in comparison is an actual system simulation environment, where an entire hardware platform is emulated, including CPU, hardware devices (PCI bus, A/D converters, FPGA, etc...) and it can run the exact same binary as the real board would.
Simics is also not restricted to vxWorks. A simics simulation could run any software: Windows, Linux, other OSes.
I agree with Benoit and would like to add that. Simics simulates how a complete system works, which often in one simulation may includes mixed technologies: multiple boards running multiple OS including VxWorks or Linux. They can connect within Simics virtual ethernet network and exchange data packets.
VxSim is much more straight forward, which only emulate one instant of VxWorks running.
I hear a lot about "Hypervisors are not emulators. If you need to emulate another hardware specifications than you computer have, you need to use emulator, not hypervisor".
Well, but yesterday I saw this video on youtube - click here - which shows how to install Win 95 on modern macOS with VMware Fusion.
The strange thing for me is that on 17:39 you could see that Win 95 virtual machine is "Pentium Pro with 64 MB RAM".
Hmm! So, Fusion somehow faked processor and RAM, right? But it is not emulator, right? So, does it mean that any hypervisor can fake processor and RAM?
At the time of its release, Windows 95 only had code to recognize CPUIDs up to Pentium Pro. Any processor not lower than Pentium Pro is "called" Pentium Pro.
The main difference is the Hypervisor cannot emulate CPU code. All code must run on the original processor.
The hypervisor does emulate the BIOS, which in tells the OS the hardware specs available; including RAM, Boot order and peripherals attached.
When you are talking about VMWare Fusion the way this works depends on how virtualization is achieved. According to wikipedia VMWare Fusion utilizes hardware-assisted virtualization, dynamic binary translation, and para-virtualization.
In the hardware-assited virtualization case, #Strom is correct and guest instructions can be executed directly on the host CPU. Besides #Strom answer, you can fake the CPU type by trapping and emulating the cpuid instruction.
In the para-virtualization case you replace critical instructions by calls to the hypervisor which emulates the instruction on behalf of the guest. So again you emulate the cpuid instruction to "fake" the CPU type. Keep in mind that this requires a modified, hence para-virtualized, guest operating system.
Finally, dynamic binary translation scans the guest code for critical instructions during runtime and either replaces them by traps into the hypervisor achieving some kind of "live para-virtualization" or translating blocks of guest code into equivalent blocks of host code that modifies the VM state according to the original guest code (this is e.g. how the QEMU full system emulator works). As a result, again you are able to "fake" the CPU type by emulating the cpuid instruction. Notice that guest and host can be the same architecture in this case, but there is no need for this.
Of course a combination of above techniques is also feasible.
As for virtualization of main memory, the hypervisor is in full control of the hardware so you can simply configure a VM with just 64MB of main memory. The VM is not able to "see" more than this due to the techniques shortly discussed above.
Please keep in mind that this just gives a very short overview of virtualization and I tried to keep it short and informative, so I know my explanations are partially not very accurate. If you are really interested in virtualization I recommend reading "Virtual Machines: Versatile Platforms for Systems and Processes" or the papers on the topic by Popek & Goldberg and "Xen and the Art of Virtualization"
I would like to have some kind of mechanism to somehow load the RAM on the Raspberry Pi programmatically from a controller computer (I assume through the SD interface) and then let the Raspberry Pi's CPU execute. Is there some kind of device that does this? And what is it programmed in?
It would also be great if there's a way to interrupt the whole thing from the controlling computer if needed.
SD is a fairly poor choice for an interface to try to push data into from an external source; generally the computer hosting the SD device wants to be the master of operations.
But the Raspberry pi has both uart serial ports and (on the model B) an ethernet interface. Downloading code through either is quite normal.
You haven't mentioned if you want to run an application atop a typical linux installation, or if you want to do bare metal programming. In the first case you would typically transfer the program to the file system (either ramdisk or the SD card) and then execute it.
In the second case, you would need a stub of code already on the device (which is to say, the boot partition of an sdcard) which knows how to configure peripherals sufficiently to enable reception of code via serial or ethernet (the latter complicated by needing a USB host stack), and then jump into it.
Is there anyway that you can expose local partition or disk image through your computer usb to another computer to appear like external drive on mac/linux/bsd system ?
I'm trying to play with something like kernel development and I need one system for compiling and other for restarting/testing.
With USB: Not a chance. USB is unidirectional, and your development system has no way of emulating a mass storage device, or any kind of other USB device.
With Firewire: Theoretically. (This is what Apple's target disk mode is using.) However, I can't find a readily available solution for that.
I'd advice you to try either virtualization or network boot. VirtualBox is free and open software, and has a variety of command line options, which means it can be scripted. Network boot takes a little effort to set up, but can work really well.
Yet another option, is to use a minimal Linux distribution as a bootstrap which sets up the environment you want, and then uses kexec to launch your kernel, possibly with GRUB as an intermediary step.
What kind of kernel are you fiddling with? If it's your own code, will the kernel operate in real or protected mode? Do you strictly need disk access, or do you just want to boot the actual kernel?