I am using a Raspberry Pi in order to communicate with a GSM/GPRS modem by USB. I am able to communicate in 115200bps. I would like to improve the communication speed as much as possible but I do not know how I should do it. The connection is RPi's USB <--> Modem's USB
I am programming in C and I have to choose the speed_t in cfsetispeed and cfsetospeed functions, which it`s maximum is B230400... I am using write function to send data.
USB 2.0 protocol has theoretically some mb/s speed so, how could I achieve this?
Unfortunately you can not achieve higher rates.
Most of GSM/GPRS modem have inbuilt USB-->Serial(RS232) Converter.
The USB port is just for USB connector compatibility.
To communicate to these modem's from any computer you need to install drivers to Emulate a RS232 connection.
In this case your board is already have those.
So basically you are doing a RS232 communication over USB lines. Your speed will be limited by RS232 standard baud-rates.
Related
My doubt is regarding the physical layer of the communication, I know from practice that for using for example teraterm to communicate with a MCU is simply enabling and configuring an UART peripheral, and then connect via USB the microcontroller and voila.
But it doesnt make sense to me yet that if USB connects to DN and DP, and an UART uses RX and TX, how does the host effectively communicates to the microcontroller?
There are two possibilities.
You connect to a USB/UART bridge such as devices made by FTDI or Prolific,
The microcontroller has a USB device controller and USB stack implementing the CDC/ACM device class (virtual COM port).
In the first instance, the bridge chip presents the CDC/ACM device to the host and exchanges data with a UART connected to the microcontroller UART. I/O control such as setting the baud rate have no impact on the USB connection, rather they are used to configure the UART link.
In the bridge arrangement, the bridge chip may be on the micro board, or it may be in a USB/serial adapter cable. Moreover internally the bridge chip is a microcontroller with a CDC/ACM device stack.
Unlike say RS-232, USB is not a peer-to-peer full duplex connection, and is not merely an electrical connection; USB requires quite complex device and host controllers and is more analogous to a device bus such as PCI than it is to UART serial connections. A CDC/ACM class device conforms to a specific protocol to allow a "virtual" UART to appear at the host. The UART you see at the PC is emulated, and is not physically the UART in the bridge.
The physical actual USB connection is a master-slave connection, with data and I/O control commands (such as baud rate and flow control) sent in USB packets to be unpacked, interpreted and transferred to the application layer via the CDC/ACM USB stack. In this arrangement the device, acting as a slave cannot initiate an exchange; rather the host continuously polls the device to which the device may return a packet containing its "tx" data. The polling and data rate of USB are fast enough to allow the simplex master-slave exchange to emulate a full-duplex UART connection, at higher throughput than can normally be achieved by a typical real UART, and certainly faster than a physical RS-xxx connection.
You can get an idea of how all this works by observing the raw USB data exchange using a tool such as WireShark. You will see that a lot more than just your application "serial" data is being exchanged.
You need to use a uart-usb interface IC that can convert uart to usb (and vice versa).
I am trying to receive and send some data from a computer to an ATtiny816 through USB. Can an ATtiny816 microcontroller communicate with a computer through USB? If yes, how should it be connected?
I'm not sure if this is possible. ATtiny 816 don't have hardware USB so you have to write software stack by yourself. Take a look on V-USB library for AVR chips. It's software USB stack for most of AVR chips.
I have second idea, but question is for what you need USB? If you want to parse some commands from computer you may use USB-UART converter and parse commands from UART interface.
I have an embedded Linux solution and want to create a command service over serial USB. The idea being that when a computer connects to my embedded via USB, they see a serial device and send serial commands to me through that port and I send responses back.
I need some help in the direction to proceed. Do I need to emulate a serial device so they see me as a COM port? Is there build in Linux solutions to broadcast my details as a serial device? Are there code examples? I can see block devices connect with my embedded solution like a USB storage device. When I plug into another computer, I would like it to see me as a serial COM port.
I just need help in the direction of which path I should go down to solve this.
Thanks in advance.
What you are looking for is the Linux USB serial gadget. The Linux USB gadgets framework allows devices to behave as a variety of standard USB devices, including serial devices, Ethernet adapters, and mass storage devices.
Note that USB gadgets will only work on targets with a USB controller that can be set to operate as a USB device. Not all USB controllers and target devices are compatible with this configuration. For instance, most PCs have a host-only USB controller, and the Raspberry Pi Model B is not compatible with gadgets because it contains an embedded USB hub upstream of the USB ports. (However, the Pi Zero is fully compatible with gadgets.)
I have LPC2148 daughter board but I am not able to dump/burn code into it, and it doesn't have any usb connector to dump code.
I read on internet by using FT232RL I can able dump code into LPC2148 but I am not able to do so.
please give me solution
thank you..!
The chip supports In-System Programming (ISP) via an on-chip boot loader ROM.
From the User Manual UM10139:
Programming of the Flash memory may be accomplished in several ways:
over the serial built-in JTAG interface, using In System Programming
(ISP) and UART0, or by means of In Application Programming (IAP)
capabilities.
The function of the FT232RL you mentioned is to act as a USB/UART bridge and is necessary primarily because modern PCs lack legacy RS-232 serial ports. You can in fact purchase a USB-Serial cable or adapter which will contain a bridge chip such as the FT232RL. Most of these use RS-232 line level signals, so you would still need an RS-232 line driver/receiver to connect then to your board (if your board has a serial port, it probably already has a line transceiver and you can connect directly to that). It is possible from specialist suppliers including FTDI themselves to get a USB cable with integrated FT232 and bare TTL level connections to connect directly to LPC2148 UART0 Rx/Tx lines.
If your board does not already expose a UART0 serial port and the necessart control to start the boot loader, a Serial Port Bootloader Interface board is available. For that you may then also need a USB/Serial adapter or a PC with a legacy serial ports.
Once you have a suitable serial connection, you will need the LPC2000 Flash Utility software to run on the PC.
The JTAG option is however faster, and more powerful since the JTAG is both a programming and debugging port. With a suitable toolchain and JTAG adapter it is possible to program and execute code with source-level PC hosted debugging including break pointing, data watching and single stepping of the code.
I am currently practising with USB programming on an AT91SAM9G20-Evaluation Kit. I learned much about USB devices and USB device port drivers while "playing" with the ATMEL provided USB device port projects (CDC-driver, ..).
But now I'd like to write a small driver to controll a wireless stick
which I plugged into one of the boards USB-A Host Ports.
I read a lot on Stack Overflow, the OpenHCI specification and even found some libraries on the net, but I am not sure if it's a good way to implement my own stack without any "good" knowledge in USB Host Port programming.
Is there a small and easy way to control the wireless-stick at the boards USB Host port? (like using the USART-Interfaces?).
I am also keen to hear hints on how to implement RTUSB or libUSB in to the AT91.
You can download AT91LIB version 1.9 from atmel from this page
The usb host libraries are under at91lib/usb/host. They're not the complete package you need though since they're just the OHCI driver -- you still need a USB driver and class drivers to implement what you want.
You could try an RTOS with USB Host support like rt-usb32