I would like to use a windows machine as a USB488/USBTMC device. USB488/USBTMC is a reimplementation of the good old GPIB/IEEE-488 on USB rails. But most articles on the topic refer to a Windows machine as a host/controller. The Windows USB stack is not well suited for USB device/USB OTG modes. However, if you look at some of the high-end gear like oscilloscopes and spectrum/network analyzers, it is well known that they are often Windows machines inside with some additional hardware. So, how it is done?
To some background: it is a project to retrofit a very old SEM microscope with new hardware. The current one is a 68k custom system with a CRT that uses a GPIB interface for comm with a PC. Things like sample spectroscopy are done as a BASIC program running on a pc and communicating through that gpib port. The plan is to replace that 68k junk with a modern day windows pc with an FPGA on a PCIe bus. For compatibility reasons, it would be nice to have a usb488 port in the new PC. Though I have no idea of how to do it properly. The only solution I have so far is to have some cheap USB-capable micro hanging on the SPI bus on the FPGA facing side and a USBTDM class on the USB side. But maybe Im missing something and there is a specific thing or chip that exists that can do it that Im not aware of.
I can only speculate how high-end oscilloscopes achieve it. The most likely option is that they use a dedicated chip like a MAX3420E. It is connected via SPI. Part of the USB protocol is implemented by the chip, part of it will be implemented by the oscilloscope software.
Most USB controllers chips found in PCs can operate as the host only. And even if they could do a role swap, Windows (for Desktop) has not supported device/peripheral mode until recently. It now does. See USB Dual Role Driver Stack Architecture. But I don't fully understand it to tell you what hardware you would need to purchase where this feature is enabled.
Role swapping is very common on smartphones. It is also implemented in Linux (search for "Linux USB gadget"). Many Apple Macs can run in Target Disk Mode, which is a USB device/peripheral mode as well.
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What is the additional advantage of developing a full UMDF windows driver if a CDC device is detected as a virtual COM port?.
I have some experience with embedded examples using a microcontroller, both communicating with a terminal like teraterm or using a dedicated USB peripheral that allows for cdc or hid functionality.
Are these drivers the ones you download and install before using any USB device? It is not clear yet what features are avaialble through the host driver.
Often on Windows the "driver" for a USB serial device is no more than an inf file that maps the device VID/PID to the Microsoft usbser.sys CDC/ACM driver.
Recent releases of Windows 10 appear to have stopped insisting that each CDC/ACM have a VID/PID specific inf file, and will load the standard driver for any device that presents as a CDC/ACM device.
The advantage of having a VID/PID specific inf file is that your device can have a vendor specific "friendly name" which can be used in applications to more easily identify your device, rather than just appearing as a generic "USB Serial Device".
One problem with Microsoft's usbser.sys driver (and Linux and Mac OS are no different) until recently was that if you disconnect the USB device, the driver is unloaded even if an application has the COM port open, and the application must close and reopen the port to recover when reconnected. I have previously used a custom driver (provided by a third party), that does not unload if an application has the port open, so that when the USB cable is reconnected, the data connection continues as normal, just as it would if it were an RS-232 cable. However, again in recent versions of Windows 10 I have noticed that usbser.sys appears to exhibit this behaviour in any case.
Note that when you do provide your own driver file, or even just a custom inf file, you will be required to go through WHQL testing in order for your device to be allowed on Windows 10, or to load without warnings on earlier versions. To do that you will need a USB.org assigned VID, an Extended Validation code-signing certificate, and either the tools and facilities to perform the testing, or pay a test house to perform the testing. That all gets somewhat expensive, and may be prohibitive for low volume, low value or non commercial products.
At one time Microsoft too charged for WHQL processing submissions, but no longer do so. That is however little combination since at the same time they changed to requiring an EV certificate and stopped a deal the used to have for low-cost certificate.
The advantage of WHQL qualification is your driver will be provided by Windows Update.
If you are using a USB serial bridge chip rather than your own USB stack and USB controller, then there is a lower cost solution. These chips can be customised with your own VID/PID and descriptors, and the vendor's existing WHQL can be associated to your device so you get all the advantages of your own driver without the costs. Most vendors will even allow you to use their VID and will assign you a unique PID so you can avoid USB.org fees. I have used this route with both Prolific and FTDI devices; it is by far the most cost effective solution.
For testing purposes I need to power off a USB device from my computer programmatically. The microprocessor in the USB device is ARM Cortex M4.
I have tried using Devcon, although the device was disabled, power was still provided to the device.
I have also tried to disable the USB root hubs ,that also didn't work.
I have read some other posts indicating that a SSR could be used, this option is not desired. I would rather choose the software solution(if there is one of course).
Some other answers have indicated that this is an OS issue, and some others a chip-set architecture issue.
So my question is what options are there available. And also is this purely something dependent on the computer side or do we need to implement something on the USB device side as well.
Thank you in advance.
I need to communicate with some custom hardware that will use either a FTDI or Silicon Labs usb to serial driver.
I found a couple examples but they are older and was hoping for a more up to date example. Plus, I have been confused by the new AppleUSBFTDI kernel driver in how that works with the IOKit and other chips like the Silicon Labs part. It would be nice to have one program that doesn’t care which driver is used.
I have already looked at this example:
FTDI Communication with USB device - Objective C
The nature of these drivers and devices is that they are supposed to function as a standard serial port virtually over USB. So in terms of access it should be no different than accessing a standard RS232 COM port.
I would suggest reading the Serial Programming Guide for POSIX Operating Systems. I'm not sure what older examples you're seeing but serial access itself is many years old, but the idea behind communicating to the serial device is the same in the case of these USB to serial bridge devices.
For information on some Objective-C frameworks, take a look at this Stack Overflow post.
Finally, here is an article directly from the Apple documentation, Working With a Serial Device, and you'll see it also references the POSIX style API.
You should simply need to install the driver associated with your device and plug it in for this to work. In terms of the Silicon Labs CP210x device just download and install the OSX driver. Then plug in your device. This is where the one difference may show up, the name of the tty device on the system (it will show up in the /dev directory). In the case of the CP210x it will show up and be accessible as tty.SLAB_USBtoUART or cu.SLAB_USBtoUART. This will be the name of the device you should open, then use and API from above to start your communication.
I have been tasked with writing a USB driver for our embedded software to send raw data to Host. This will be used to send some logging data to host. We are using iMX31 litekit for development.
From the documents that I have read on USB, my understanding is that the embedded device will be in device mode only. Also it will only be communicating with host machine.
So can any one guide me here? Any article, reference or code is welcome.
Some things to consider:
Is this a high bandwidth device like a camera or data recorder, or a low bandwidth device?
For low bandwidth, I would strongly consider making your device act as a USB HID class. This is the device class that supports keyboards, mice, joysticks, gamepads, and the like. It is relatively easy to send data to nearly any application, and it generally doesn't require that you write a custom device driver on the host side. That latter feature alone is often worth the cost of lightly contorting your data into the shape assumed by the HID class. All the desktop operating systems that do USB can use HID devices, so you get broad compatibility fairly easily.
For high bandwidth, you would still be better served if your device fits one of the well established device classes, where a stock device driver on the host end of the wire can be used. One approach that often works is to use the Mass Storage class, and emulate a disk drive containing one file. Then, your device simply mounts on the host as if it were a disk, and you communicate by reading and writing to one (or a few) file.
I would expect there to be a fair amount of sample code out there for any serious USB device chipset that implements either or both of HID and Mass Storage.
If you really must wander into fully custom device territory, then you will need to be building device drivers for each host platform. The open source libusb library can be of some help, if its license is compatible with your project. There are also ways in newer versions of Windows to develop USB drivers that run in user mode using the User Mode Driver Framework that have many of the same advantages of libusb, but are not portable off the Windows platform.
The last custom device I worked on was based on a Cypress device, and we were able to ship their driver and an associated DLL to make our application code easier to build. I don't know off the cuff if there is any equivalent available for your device.
For a really good overview, I recommend the USB FAQ, and the latest edition of Jan's book, USB Complete.
The rest of my team will make for my application a simple non-standard USB microphone, but until they finish it I will have to emulate it, for integration testing purposes.
Is there any risk in a physical loopback? Yes there is
Will a physical loopback work? Only with a USB bridge
There is any way to create a logical loopback? (MSDN has something about this)
There is any general purpose USB emulator software?
In case there is many options available I'd rather work it .NET/Matlab/Python solutions.
Edit: Proof of concept here
I strongly recommend this project, USB IP. It is a way of connecting USB devices over the network. There is a Windows client.
What this means is, you install the client on your Windows computer.
This device then expects to talk to a USB device connected to a Linux computer, the server:
What you now do, is either create a fake device driver for Linux, that looks like is connected to a physical USB device, but in reality is just logic pretending to be your USB device. There are tutorials for writing USB drivers for Linux. Or you create your own stub driver for the Device Control Manager (see picture above). This stub driver could run on Windows or Linux, it wouldn't matter. It could even run on the same Windows machine which is the USB client.
The DSF USB Loopback Device mentioned in the question itself, would be the same kind of solution as a stub driver for the Device Control Manager, but taking Linux out of the picture altogether.
You can write virtual USB device using QEMU.
You can duplicate already existing device, like the dev-serial.c found in this QEMU repository and change it for your needs.
After you write and compile your USB device you can simply attach it to your VM using the QEMU command line interface.