I want to connect a USB peripherals to a FPGA. Basically FPGA should act like an USB host. Is there a FPGA board support a USB hub so that one could connect multiple(upto 4) USB peripherals at a time.
I have a Digilent Nexys3 fpga which is based on Spartan 6. It supports only one USB device (keyboard or mouse). It doesn't support a hub. I have found Cypress host controllers, but I am not sure how to use it in a FPGA.
You need to have a USB host controller inside your FPGA, such IP is not freely available, one alternative is to use a Zynq based (for Xilinx) or Cyclone V based (for Altera) board. Those have integrated USB controllers connected to their dual ARM core.
You can find more info about those at:
Altera Cyclone V
Xilinx Zynq
You maybe able to use an external host controller but then you have to connect it to your FPGA and that is usually requires a lot of IOs and those modules are more expensive than buying a Zed board ($395) or Cyclone V board ($450).
Related
Wondering how can the PC distinguish among multiple USBs. For example, when i plug my flash drive USB into my computer how can it know that it is a flash drive USB not a keyboard USB ?
Thanks in advance.
in the USB standard there are USB classes a memory stick is USB mass storage class, keyboard, mouse, joystick are USB HID class (Human Interface Device), cameras implement USB PTP (picture transfer protocol), USB-to-serial (virtual COM ports,...) is USB CDC ACM class ,...
the following link lists all USB classes for that windows has drivers https://msdn.microsoft.com/en-us/library/windows/hardware/ff538820%28v=vs.85%29.aspx
when the USB device is plugged in there is a communication between the MCU on the USB device (firmware) and the PC (USB host) . in this communication the device says which USB class it it and the host loads the fitting driver
you can sniff this communication using wireshark or see dmesg (on linux)
this communication is very low-level and not easily human-readable. there are tools like wireshark or lsusb -v for this
a USB device has to implement a special hierarchy of descriptors in which information of the internal structure of the USB device is contained. the hierachy is:
device descriptor -> configuration descriptor -> interface descriptor -> endpoint descriptor
EP0 is reserved for control transfers, else any transfer has to go to or come from an endpoint (OUT endpoint / IN endpoint)
see http://www.beyondlogic.org/usbnutshell/usb1.shtml
USB is a higly complex standard because it implements a wide functionality for a large number of different devices in one physical interface. i think the most complicated USB class standard is USB audio...
Hopefully I will have more luck today. I have no prior USB integration and about 8 months of learning embedded systems on Atmel devices. I am trying to use an Atmel SAM L series to connect over USB to a computer. The use case is for data transfer. Specifically, the MCU will be gathering data from it's sensors and packaging it for USB transfer.
I have searched through and read up on all of Atmel's included USB examples. I have also started reading through usb.org's class specifications for CDC.
I have running now something that lets me send data along one com port, into the target usb and then out the debugger usb to another com port. However, I don't think this is real USB.
My problem is two fold.
1.) I do not fully understand what differentiates USB from serial communication on a com port.
2.) Even if I were doing it correctly, I'm not sure how to test and verify that I have indeed created a legitimate USB device that can be accepted by a host computer.
Links to documentation(Atmel or generic) or example code would be appreciated.
1) USB is defined in the USB specifications from http://www.usb.org. Serial ports were an older and simpler interface that involved sending data back and forth asynchonously on pins with names like TX and RX. The USB CDC class and its ACM subclass allow you to make a USB device that emulates a serial port. If you make your device be a USB CDC ACM device, then you don't need to supply any drivers for Windows 10, Linux, or Mac OS X.
2) You can read the USB specification and the CDC ACM specification. You can run the USB command verifier. You can test your device with a variety of different USB hosts to make sure it works.
I'm trying to implement UART over a USB interface on the STM324x9I-EVAL development board. The purpose is to send commands to a servo controller (or other hardware, for that matter) serially. I've successfully implemented the USB_Device_CDC example on the development board but am unsure exactly how this works without a PC with drivers on the other end. As far as other hardware is concerned, will the USB port now simply look like a serial port? Or is there still a need for a driver or some sort of interface on the other end?
I do want to point out that I'm aware of the following post:
Emulating UART over USB
but I don't believe my question is fully answered within the context of that answer.
A USB connection is not a peer-to-peer connection like a UART. It requires a host and a device in a master/slave relationship. The device cannot initiate data transfer; it must be continuously polled by the by the host.
A CDC/ACM class device presents a virtual COM port on a PC host, but that does not allow the device to communicate with a UART interface. It looks like a serial port at the software level, but does not implement a UART physical layer. There is an awful lot going on under the hood to make it look like a PC serial port, but none of it resembles UART communications at the physical level.
There are devices that act as UART/USB bridges (from FTDI and Prolific for example), and you could (somewhat expensively) build your own from a microcontroller that has a USB device controller and a UART, but the bridge is a USB device and must still connect to a USB host; these are normally used to connect a PC to a microcontroller that lacks a USB controller or where the software/CPU overhead of using a USB controller is too great.
In theory you could connect a microcontroller that has a USB host controller to one that has a USB device controller, but you need host and device software stacks on each respectively, and once you have the USB connection, implementing CDC/ACM is a somewhat inefficient use of the available bandwidth. The purpose of the CDC/ACM class is primarily to allow "legacy" software to work on a PC.
If you need to connect to a "real" serial port, you should use a real UART - which are far more ubiquitous than USB controllers on microcontrollers in any case.
You should learn a little bit about USB device classes. CDC is a USB device class, and ACM is a subclass that I assume you are using. The device you made could be called a "CDC ACM device" because it uses the CDC class and the ACM subclass.
These classes and subclasses are defined by the USB Implementers Forum in documents that you can find here:
http://www.usb.org/developers/docs/devclass_docs/
These documents specify things like what USB descriptors a CDC ACM device should have in order to describe itself to the host, and what kinds of interfaces and endpoints it should have, and how serial data will be represented in terms of USB transactions and transfers.
Note that CDC ACM only specifies some USB commands for transferring data between the host and the device. It does not specify what the device will actually do with that data. You can use CDC ACM to implement a USB-to-serial adapter, or you can just use it as a general purpose communication interface for whatever data you want to send.
Yes, you do need a driver on the PC side. The driver needs to be designed to run on your specific operating system. It needs to create some kind of virtual serial port device in your operating system that other software (which only knows about serial ports) can find and connect to. It needs to translate serial port operations performed by other software on the serial port (e.g. writing some bytes to the serial port) into low-level USB commands according to the CDC ACM specifications (e.g. sending some bytes out to the device on a particular endpoint in the form of USB packets). It needs to somehow know which USB devices it should operate on, since not every USB device is a CDC ACM device.
For Windows, you will probably use the usbser.sys driver which comes with Windows. For versions of Windows older than Windows 10, you will need to write an INF file to associate your device to usbser.sys and sign it. For Windows 10 and later, there is a new INF file called usbser.inf already included with Windows which will automatically match any valid CDC ACM device. This means you don't have to write or distribute a driver for CDC ACM devices if you only intend to support using the device on Windows 10 or later. The partnership between Microsoft and Arduino which began in 2015 gives me hope that Microsoft will continue supporting and improving usbser.sys in the future. In fact, they claim that in Windows 10 "the driver has been rewritten by using the Kernel-Mode Driver Framework that improves the overall stability of the driver", so that is good news.
For Linux, there is the cdc_acm kernel module, which has been a standard part of the kernel for a long time and should work automatically with any CDC ACM device you plug in.
For Mac OS X, there is the AppleUSBCDCACM driver, which should work automatically with any CDC ACM device you plug in.
Note that for any of these drivers to recognize your device and work with it, your device has to have certain values in its USB descriptors, and the requirements can vary depending on what exact driver version you are talking about.
Will the USB port now simply look like a serial port?
No, that's the wrong way to think about it. The USB port will still look like a USB port, but the various USB drivers provided by your operating system will recognize that a CDC ACM device is plugged into that port and create a new entry in your operating system's list of serial ports. Then if you run some software that only knows about serial ports, it can connect to that port.
In fact, if you make a composite device, you can have a single USB device plugged into a single USB port that actually has two or more virtual serial ports.
When I plug a USB web Camera into a PC via USB, what communications is used? I know each device COULD have its own uniques driver, but it seems as though 99% use a common built in driver now. Where is it spec'd and how do you get a linux embedded device to act like a webcam?
What you're looking for is the USB Video Class and you can download the specification for this and other standard USB device classes here:
http://www.usb.org/developers/docs/devclass_docs/
The Linux USB gadget framework has code to emulate such a device:
https://github.com/torvalds/linux/blob/master/drivers/usb/gadget/function/f_uvc.c
I'm looking to control a bunch of LEDs from my computer, with a TI MSP430 or similar.
My computer is a Macbook Air, and so it looks like the only port I can communicate with is USB. The MSP430 has a USB port, but I can't find any information about using the USB port for anything besides programming the chip. Is there a way around this, to use USB to communicate with the board?
Thanks!
If you are using one of the processors with built in USB hardware then you should look at this Texas Instruments Page which describes the capabilities of the MSP USB. It includes links to the USB software stack that you will need to implement an HID class device.
I see two more options here. You can also use:
a) USB <-> LPT adapter to control the LEDs directly — in this case the schematics are extremely simple. See how it's done;
b) USB <-> COM or USB <-> RS232 adapter to communicate with the controller via RS232 — in this case you'll have to implement some simple protocol for communication with the controller, but the whole solution would still be much simpler than the one with USB.
The MSP430 Series 5 and Series 6 micro controllers (i.e. MSP430x6xx and MSP430x5xx) have built in USB modules that allow communication from PC and could be used to control the MSP430 via USB. Download the MSP430 USB Developers package here: http://www.ti.com/tool/msp430usbdevpack and use the USB CDC or HID API stacks to develop an application as per your requirements. In case you are using CDC(COM port) you may use a Terminal program to send the commands to control LEDs or if you use the HID stack, you may use the hidDemo PC software included in the Developers package to send/receive commands.