Throughout this USB series, different types of USB devices have been designed and developed. These devices were enumerating with the host computer and then were using Class Specific transfers for further USB communication. Like the Keyboard, Mouse and joystick devices were using interrupt transfers for their operations after enumeration. Similarly, the audio class devices were using isochronous transfers for their operations after enumeration. The CDC Class devices were using bulk transfers for their operations after enumeration. Any of these transfers (Bulk, Isochronous or Interrupt) are enabled only after the control transfer which let the device get enumerated with the host. These transfers are required when data is also sent from the device to the host computer.
In this project, an USB device to control an LED series will be designed. The device will not send any data to the host computer but will only read data from the host computer and control LEDs accordingly. In such type of USB communication, only control transfer is sufficient to implement the device functioning and so only Endpoint 0 is involved in the USB communication.
The project will need a controller chip to handle USB data from the computer and to operate LED series accordingly. The 8-bit USB AVR – Atmega 32u4 is used as the device controller chip in the project. The project uses AVR based Lightweight USB Framework (LUFA) as the firmware which will be modified to implement the project’s functioning. The device is tested on a Linux system using Pyusb and Libusb frameworks for sending data from computer to the device.
Fig. 1: Prototype of Arduino based USB Controlled LED Series
The Generic HID device driver class of the LUFA firmware is used and modified to program the project. With the use of LUFA firmware, the device driver code to implement USB protocol is not needed to be written explicitly. Modifying the firmware code will be sufficient to implement the USB protocol. The device has four LEDs connected to it which will be switched ON or OFF from the computer.
PREREQUISITES
This project is based on Arduino Pro Micro which has the USB AVR – Atmega 32u4 as the sitting MCU. In order to understand this project, one must have basic knowledge of the AVR microcontrollers and the embedded C programming for AVRs. WinAVR Studio is used to write, edit and compile the project code, so closely following the project shall require familiarizing with the above stated IDE as well. Though LUFA framework takes care of implementing the USB protocol and has APIs to abstract the lower level codes, understanding USB protocol is recommended to understand how actually the project is working. In fact, if anyone has already worked on some other microcontroller, it will not be much pain to understand and follow this project as the project code is more or less about modifying the LUFA device driver to work as generic HID device and receiving digital output at the Arduino pins.
COMPONENTS REQUIRED
1. Arduino Pro Micro
2. Breadboard
3. Connecting wires
4. LEDs
5. Micro USB cable
6. 10K resistors
SOFTWARE TOOLS REQUIRED
1. WinAVR Studio
2. AVR Dude
5. Pyserial 2.7
BLOCK DIAGRAM
Fig. 2: Block Diagram of Arduino based USB Controlled LED Series
CIRCUIT CONNECTIONS
The project uses Arduino Pro Micro as the USB controller chip. A series of four LEDs is connected at the port B of the Arduino. The LEDs are connected at pins 2, 4, 5 and 6 of the port B. The 220 Ω pull up resistors are used to interface the LEDs. The LEDs are connected between the pins and the ground with anode connected to the pin and cathode connected to the ground. Therefore, when a HIGH logic is output from the pin, the LED starts glowing and when a LOW logic is output from the pin, the LED stops glowing.
The Program code for the project is burnt to the Arduino Pro Micro using AVR Dude. The Arduino board is connected to the USB port of a PC by a USB cable.
HOW THE PROJECT WORKS
In this project the USB protocol is implemented by the LUFA framework. For configuring the controller chip to work as Generic HID device, the HID Class Driver of the LUFA framework will be used. The Human Interface Device (HID) class takes care of the transfers between the host device and the human controlled USB peripherals like USB Keyboard, Mouse or Joystick. However, the Generic HID device made in this project only handles to receive data from the host computer.
When a USB device is attached to the host (PC), the host sends request for configuration details in the form of control transfer. The connected device has to respond with appropriate descriptors to get configured and ready for further operations. Only after configuration, the device can communicate with the host in the form of interrupt, isochronous or bulk transfers for executing the operations for which the device has been made. This process of identification and configuration of the device with the host is called enumeration.
Fig. 3: Image of Arduino based USB Controlled LED Series
In case of LED series, after configuring with the host device, it has to communicate with the host in the form of control transfers only for reading data from the host computer. The Control Transfer can also be used to exchange data between Device and PC like the other transfer types. The Class Specific Requests of Control Transfer will be used to send data from Host (PC) to the Device (Microcontroller).
In HID class, two types of Transfer Types are used: Control Transfer and Interrupt Transfer. Generally, the Interrupt Transfer is used to send Data Reports. But the Control Transfer can also be used when Interrupt Endpoints are not declared or available. The Default Control Endpoints (Endpoint 0) are always available so control transfer can also be used to send or receive data anytime. The data can be exchanged using Class-Specific Requests. These Requests are sent by Host to Device via Control Transfer. The Set_Report is the request by which Host can send data to Device. The Set_Report request is structured in the following manner -:
Fig. 4: Table listing data structure of Set_Report request
The data will be transferred using Data Packet or Data Report. The Data Report (Data Packet) will contain four bytes. These bytes will be used to indicate the device to switch ON/OFF the LEDs. Therefore the LEDs and data report received by control transfer from the host computer will be related in the following manner -:
Fig. 5: Table listing Data Packet structure for LED Series Control
The project is based HID class driver of USB and LUFA framework has HID class related module in the LUFA-Source-Folder /LUFA/Drivers/USB/Class/Device folder. Other device class related module are also in the same folder. The LUFA framework has demo projects for different USB device classes in the LUFA-Source-FolderDemosDeviceClassDriver folder. For implementing the project, demo project for Generic HID devices provided in the LUFA framework will be modified and complied. The demo project for Generic HID devices is in the LUFA-Source-FolderDemosDeviceClassDriverGenericHID folder. The folder contains GenericHID.c file which will be modified to implement the LED project.
How GenericHID.c identifies HID device being Generic HID device
The GenericHID.c uses Generic_HID_Interface interface in HID_Device_USBTask() function which is being imported from the HIDDeviceClass.c (from LUFA-Source-Folder LUFADriversUSBClassDevice) to configure the device as generic HID device. The interface abstracts the low-level descriptor codes and identifies the device as generic HID device through an InterfaceNumber variable.
Generic HID Device Specific Report Descriptors
Any HID device has to exchange data with the host which should be structured in the form of reports. The report descriptor defines the report structure. A report descriptor contains the information needed by host to determine the data format and how the data should be processed by the host. Therefore, a report descriptor basically structure the data that needs to be exchanged with the host according to the USB protocol.
For working like a generic USB HID device, the device needs to send usage report descriptor specific to Generic HID Class to the host while it itself needs to interpret data output report specific to Generic HID Class received from the host device. The Usage Report informs the Host about the features or functionality of the USB device whereas the Data Output Report is used to receive data from the host. The Generic HID Class can also send data to the host computer in the form of Data Input Report but that feature will not be used by the project.
Fig. 6: Screenshot of Data Input Report from USB LED Series Controller
From Where GenericHID.C gets the USAGE and Data Reports Descriptors
In the LUFA framework’s demo project for GenericHID, GenericHID.h is imported. The GenericHID.h imports descriptor.c file which defines the relevant usage and data reports descriptors for the host device.
The descriptor.c defines a GenericReport[] structure to generate generic HID usage and data reports descriptors. Inside descriptor.c the GenericReport[] structure has the values returned by HID_DESCRIPTOR_VENDOR () function. The HID_DESCRIPTOR_VENDOR () is defined in HIDClassCommon.h (located in LUFA-Source-FolderLUFADriversUSBClassCommon folder). The GenericHID.c imports GenericHID.h which imports usb.h. USB.h imports HIDCLass.h. In HIDClass.h is imported HIDClassDevice.h if the USB_CAN_BE_DEVICE is true for the controller chip to being a USB device not the host. The HIDClassDevice.h imports HIDClassCommon.h where the HID device specific descriptor fields have been defined.
USAGE REPORT
HID_DESCRIPTOR_VENDOR () returns the field values of the usage report descriptor, specific to generic HID device functioning. The fields are set to following values in HID_DESCRIPTOR_VENDOR ().
Fig. 7: Screenshot of HID_DESCRIPTOR_VENDOR Function in LUFA Library
The Usage or Feature report contains information about the features of the device. In other words, this report informs Host about the features needed in the device. A generic HID device is a vender defined device and can simply send or data on the USB interface.
DATA OUTPUT REPORT
The Data Output report for generic HID device simply contains data of a size restricted by the usage report. It is defined in the following manner -:
Fig. 8: Screenshot of Data Output report for generic HID device in LUFA Library
HOW THE DEVICE WORKS
The device will receive data from the host computer on control transfer. Since, data is to be received from the host device CALLBACK_HID_Device_ProcessHIDReport() function of the GenericHID.c will be modified. The main() function of the GenericHID.c will also be modified to acknowledge the microcontroller about the circuit configuration. On PC side, a Python Application will be used to control switching of LEDS. The Application will be based on Python programming language and will run on Linux distribution like Ubuntu. It will use Pyusb and Libusb framework for sending data on the USB protocol. The Application will issue a Set_Report request to transfer the data to Device (microcontroller).
Check out the program code to see the modifications implemented for the project.
PROGRAMMING GUIDE
For building the project download the LUFA framework from the github.com. The demo project provided with the LUFA framework is modified to make the project. In the extracted LUFA zip file, open Demos/Device/ClassDriver/GenericHID folder. The folder has the following files and folders.
Fig. 9: Screenshot of LUFA Library Folder on Windows
Of these, GenericHID.h, GenericHID.c and Makefile needs to be modified for this project. The modified files (provided at the bottom of the article in zip format) can also be downloaded from the engineersgarage and replaced with the original files. Either open the files in WinAVR Studio or Notepad++ and modify original files or replace files with the already modified one. The modified or replaced GenericHID.c needs to be compiled from within the LUFA’s Source folder to get the object code.
A python script has been written to run on the desktop side. The script can be written and saved as a file during testing this USB device or it can be downloaded along with the other project files from engineersgarage and run using command prompt or a command line interpreter during testing of the device.
Modifying GenericHID.h
The GenericHID.h library file is imported in the GenericHID.c file and includes a set of additional libraries and defines the constants and functions for the Generic HID device. These include the additional libraries for the LED board which should be commented out as the project is not using that HID feature. So open GenericHID.h and make the following changes -:
• Comment the #include library statements for LEDs.h (We are commenting this library as we are not using LED board)
Save the file with changes.
Modifying GenericHID.C file
Again in the GenericHID.c, the code sections for LED board needs to be commented out. So open GenericHID.c and make the following changes -:
• In the main loop, comment the LEDs_SetAllLEDs()
• In SetupHardware() function, comment the LEDs_Init()
• In EVENT_USB_Device_Connect() function, comment the LEDs_SetAllLEDs()
• In EVENT_USB_Device_Disconnect() function, comment LEDs_SetAllLEDs()
• In EVENT_USB_Device_ConfigurationChanged() function, comment the LEDs_SetAllLEDs()
In the main() function of GenericHID.c the microcontroller needs to be made aware of the circuit configuration. Inside the main function Port B where the LEds have been connected needs to be defined as output and all the pins of port B has to be raised to LOW logic by default as the LEDs should remain in OFF state by default. So add the following statements in the beginning of main() function.
Inside the infinite for loop the HID_Device_USBTask() function is called where Generic_HID_Interface interface is passed as parameter. The interface identifies the device as Generic HID device and abstracts the low level program code specific to Generic HID class. The function is coming from the HIDClassDevice.c module (located in LUFA/Drivers/USB/Class/Device/HIDClassDevice.c) and is used for general management task for a given HID class interface, required for the correct operation of the interface. It should be called in the main program loop, before the master USB management task USB_USBTask(). The USB_USBTask() is the main USB management task. The USB driver requires this task to be executed continuously when the USB system is active (device attached in host mode, or attached to a host in device mode) in order to manage USB communications. The function is defined in USBTask.c (Located in LUFA-Source-FolderLUFADriversUSBCore folder).
For creating the Data Output report CALLBACK_HID_Device_ProcessHIDReport() function needs to be modified. The default file has the function body to transmit data to an LED board.
Fig. 10: Screenshot of CALLBACK_HID_Device_ProcessHIDReport Function of LUFA Library
The controller chip receives 4-byte data from the host computer and according to that data, it changes the status of LEDs. If 0x00 is received in a byte, a LOW logic is sent to the respective pin switching the respective LED OFF. If 0x01 is received in a byte, a HIGH logic is sent to the respective pin switching the respective LED ON. So replace the body of the function with the following code -:
The Data Input Report (to send data from device to the host) is handled by the CALLBACK_HID_Device_CreateHIDReport() function. In the unedited LUFA file, this function has statements to report back the status of LED board and has the following body.
Fig. 11: Screenshot of CALLBACK_HID_Device_CreateHIDReport Function of LUFA Library
All the statements in this function will be cleared as the device will not send any data to the host computer. Therefore, the CALLBACK_HID_Device_CreateHIDReport() function will be left with an empty body.
Save the file and create Make file for the project.
Modifying Make File
In the GenericHID folder there is a make file that needs to be edited. The file can be edited using Notepad++. The following information needs to be edited -:
• MCU = atmega32u4
• ARCH = AVR8
• BOARD = LEONARDO
• F_CPU = 16000000
Save the file and exit. Now all the files are edited completely for the LED Series Project.
Compiling GenericHID.c
For compiling the source code, WinAVR Programmers Notepad or Arduino IDE can be used. Open the modified GeericHID.c file and compile the code.
BURNING HEX CODE
The hex file is generated on compiling the GenericHID.c file. For burning the object code to microcontroller open the Command Prompt, change the current directory to the directory containing the Hex file. This can be done using command: CD <address of the directory>. Now reset the Arduino and instantly run the command: avrdude -v -p atmega32u4 -c avr109 -P COM20 -b 57600 -D -Uflash:w:GenericHID.hex:i after replacing the COM Port with the recognized one. If using Linux, the COM port name will be like /dev/ttyACM0.
TESTING THE DEVICE
In the next project – Atmega 32u4 Based USB LED Status, learn how to use interrupt transfer for sending data from microcontroller to the host computer.
Project Source Code
###
/* LUFA Library Copyright (C) Dean Camera, 2015. dean [at] fourwalledcubicle [dot] com www.lufa-lib.org */ /* Copyright 2015 Dean Camera (dean [at] fourwalledcubicle [dot] com) Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that the copyright notice and this permission notice and warranty disclaimer appear in supporting documentation, and that the name of the author not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. The author disclaims all warranties with regard to this software, including all implied warranties of merchantability and fitness. In no event shall the author be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of this software. */ /** file * * Main source file for the GenericHID demo. This file contains the main tasks of * the demo and is responsible for the initial application hardware configuration. */ #include "GenericHID.h" /** Buffer to hold the previously generated HID report, for comparison purposes inside the HID class driver. */ static uint8_t PrevHIDReportBuffer[GENERIC_REPORT_SIZE]; /** LUFA HID Class driver interface configuration and state information. This structure is * passed to all HID Class driver functions, so that multiple instances of the same class * within a device can be differentiated from one another. */ USB_ClassInfo_HID_Device_t Generic_HID_Interface = { .Config = { .InterfaceNumber = INTERFACE_ID_GenericHID, .ReportINEndpoint = { .Address = GENERIC_IN_EPADDR, .Size = GENERIC_EPSIZE, .Banks = 1, }, .PrevReportINBuffer = PrevHIDReportBuffer, .PrevReportINBufferSize = sizeof(PrevHIDReportBuffer), }, }; /** Main program entry point. This routine contains the overall program flow, including initial * setup of all components and the main program loop. */ int main(void) { SetupHardware(); DDRB = 0xff; // make PORTB as output port PORTB = 0x00; // make all pins low //LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY); GlobalInterruptEnable(); for (;;) { HID_Device_USBTask(&Generic_HID_Interface); USB_USBTask(); } } /** Configures the board hardware and chip peripherals for the demo's functionality. */ void SetupHardware(void) { #if (ARCH == ARCH_AVR8) /* Disable watchdog if enabled by bootloader/fuses */ MCUSR &= ~(1 << WDRF); wdt_disable(); /* Disable clock division */ clock_prescale_set(clock_div_1); #elif (ARCH == ARCH_XMEGA) /* Start the PLL to multiply the 2MHz RC oscillator to 32MHz and switch the CPU core to run from it */ XMEGACLK_StartPLL(CLOCK_SRC_INT_RC2MHZ, 2000000, F_CPU); XMEGACLK_SetCPUClockSource(CLOCK_SRC_PLL); /* Start the 32MHz internal RC oscillator and start the DFLL to increase it to 48MHz using the USB SOF as a reference */ XMEGACLK_StartInternalOscillator(CLOCK_SRC_INT_RC32MHZ); XMEGACLK_StartDFLL(CLOCK_SRC_INT_RC32MHZ, DFLL_REF_INT_USBSOF, F_USB); PMIC.CTRL = PMIC_LOLVLEN_bm | PMIC_MEDLVLEN_bm | PMIC_HILVLEN_bm; #endif /* Hardware Initialization */ //LEDs_Init(); USB_Init(); } /** Event handler for the library USB Connection event. */ void EVENT_USB_Device_Connect(void) { //LEDs_SetAllLEDs(LEDMASK_USB_ENUMERATING); } /** Event handler for the library USB Disconnection event. */ void EVENT_USB_Device_Disconnect(void) { //LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY); } /** Event handler for the library USB Configuration Changed event. */ void EVENT_USB_Device_ConfigurationChanged(void) { bool ConfigSuccess = true; ConfigSuccess &= HID_Device_ConfigureEndpoints(&Generic_HID_Interface); USB_Device_EnableSOFEvents(); //LEDs_SetAllLEDs(ConfigSuccess ? LEDMASK_USB_READY : LEDMASK_USB_ERROR); } /** Event handler for the library USB Control Request reception event. */ void EVENT_USB_Device_ControlRequest(void) { HID_Device_ProcessControlRequest(&Generic_HID_Interface); } /** Event handler for the USB device Start Of Frame event. */ void EVENT_USB_Device_StartOfFrame(void) { HID_Device_MillisecondElapsed(&Generic_HID_Interface); } /** HID class driver callback function for the creation of HID reports to the host. * * param[in] HIDInterfaceInfo Pointer to the HID class interface configuration structure being referenced * param[in,out] ReportID Report ID requested by the host if non-zero, otherwise callback should set to the generated report ID * param[in] ReportType Type of the report to create, either HID_REPORT_ITEM_In or HID_REPORT_ITEM_Feature * param[out] ReportData Pointer to a buffer where the created report should be stored * param[out] ReportSize Number of bytes written in the report (or zero if no report is to be sent) * * return Boolean c true to force the sending of the report, c false to let the library determine if it needs to be sent */ bool CALLBACK_HID_Device_CreateHIDReport(USB_ClassInfo_HID_Device_t* const HIDInterfaceInfo, uint8_t* const ReportID, const uint8_t ReportType, void* ReportData, uint16_t* const ReportSize) { } /** HID class driver callback function for the processing of HID reports from the host. * * param[in] HIDInterfaceInfo Pointer to the HID class interface configuration structure being referenced * param[in] ReportID Report ID of the received report from the host * param[in] ReportType The type of report that the host has sent, either HID_REPORT_ITEM_Out or HID_REPORT_ITEM_Feature * param[in] ReportData Pointer to a buffer where the received report has been stored * param[in] ReportSize Size in bytes of the received HID report */ void CALLBACK_HID_Device_ProcessHIDReport(USB_ClassInfo_HID_Device_t* const HIDInterfaceInfo, const uint8_t ReportID, const uint8_t ReportType, const void* ReportData, const uint16_t ReportSize) { uint8_t* Data = (uint8_t*)ReportData; if (Data[0] == 0x01) PORTB |= 0b00010000; // switch on led1 else PORTB &= 0b11101111; // switch off led1 if (Data[1] == 0x01) PORTB |= 0b00100000; // switch on led2 else PORTB &= 0b11011111; // switch off led2 if (Data[2] == 0x01) PORTB |= 0b01000000; // switch on led3 else PORTB &= 0b10111111; // switch off led3 if (Data[3] == 0x01) PORTB |= 0b00000100; // switch on led4 else PORTB &= 0b11111011; // switch off led4 }###
Circuit Diagrams
Project Video
Filed Under: Electronic Projects
Filed Under: Electronic Projects
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