CDC: Communication Device Class (ACM)

Implement application specific behavior of a Communication Device Class (CDC) USB Device using the sub-class Abstract Control Model (ACM). More...

Content
	User API
	User API reference of the Communication Device Class (ACM).
	Configuration
	Configuration of the USB Device CDC (ACM) Class in µVision.

Description

Implement application specific behavior of a Communication Device Class (CDC) USB Device using the sub-class Abstract Control Model (ACM).

The CDC (ACM) class in the USB Component is used for data communication. You can typically use it in applications that previously used a serial COM or UART communication.

Refer to:

• CDC: Communication Device Class for an overview of the CDC class.
• USB Device Virtual COM Port example project.

The USB Component allows multiple instances of the CDC class. This feature is used to create USB Composite Devices. Each CDC class instance has a separate files and interface functions:

• A CDC configuration file USBD_Config_CDC_n.h.
• An application specific user source code file which may be implemented with the user code template USBD_User_CDC_ACM_n.c.
• Functions that start with the prefix USBD_CDCn_ACM are available for each instance of a CDC ACM class.

This documentation uses n as a placeholder for the instance number 0 - 3. Most applications only require one instance of a CDC ACM class. For the first CDC ACM class instance the instance number is 0:

• USBD_Config_CDC_0.h
• USBD_User_CDC_ACM_0.c
• The function prefix is USBD_CDC0_ACM

Descriptor Requirements

The following descriptors are required in an USB CDC ACM Device:

• Standard Device Descriptor
• Standard Configuration Descriptor
• Interface Association Descriptor
• CDC Header Functional Descriptor
• CDC Union Functional Descriptor
• Call Management Functional Descriptor
• Abstract Control Management Functional Descriptor
• Standard Interface Descriptor for the CDC Class communication interface
• Standard Endpoint Descriptor for Interrupt IN endpoint
• Standard Interface Descriptor for the CDC Class data interface
• Standard Endpoint Descriptors for Bulk IN and Bulk OUT endpoints

The necessary descriptors are automatically generated by the USB Middleware Component. The page USB Descriptors provides more information on the topic.

Software Structure

The handling for the CDC class endpoint events is implemented in USBD_CDCn_Int_Thread and USBD_CDCn_Bulk_Thread which are started by USBD_Initialize. Each instance of a CDC class runs an instance of USBD_CDCn_Int_Thread and USBD_CDCn_Bulk_Thread.

The thread USBD_CDCn_Int_Thread handles Interrupt IN Endpoint whereas the USBD_CDCn_Bulk_Thread handles the Bulk IN and Bulk OUT Endpoints.

Implementation

To create an USB Device with a CDC ACM class:

• Set the required number for USB:Device:CDC class instances during the RTE Component Selection.
• Set the parameters in the configuration file USBD_Config_CDC_n.h.
• Implement the application specific behavior using this template.

User Code Template USBD_User_CDC_ACM_n.c

The following source code contains all the required callback functions and can be used to implement the application specific behavior of a USB CDC (ACM) Device.

/*------------------------------------------------------------------------------
 * MDK Middleware - Component ::USB:Device
 * Copyright (c) 2004-2015 ARM Germany GmbH. All rights reserved.
 *------------------------------------------------------------------------------
 * Name:    USBD_User_CDC_ACM_n.c
 * Purpose: USB Device Communication Device Class (CDC)
 *          Abstract Control Model (ACM) User module
 * Rev.:    V6.2
 *----------------------------------------------------------------------------*/

 
#include <stdbool.h>
#include "rl_usb.h"
 
// Called during USBD_Initialize to initialize the USB CDC class instance (ACM).
void USBD_CDCn_ACM_Initialize (void) {
  // Add code for initialization
}
 
 
// Called during USBD_Uninitialize to de-initialize the USB CDC class instance (ACM).
void USBD_CDCn_ACM_Uninitialize (void) {
  // Add code for de-initialization
}
 
 
// Called upon USB Bus Reset Event.
void USBD_CDCn_ACM_Reset (void) {
  // Add code for reset
}
 
 
// Called upon USB Host request to change communication settings.
// \param[in]   line_coding   pointer to \ref CDC_LINE_CODING structure.
// \return      true          set line coding request processed.
// \return      false         set line coding request not supported or not processed.
bool USBD_CDCn_ACM_SetLineCoding (CDC_LINE_CODING *line_coding) {
  // Add code for set line coding
 
  return true;
}
 
 
// Called upon USB Host request to retrieve communication settings.
// \param[out]  line_coding   pointer to \ref CDC_LINE_CODING structure.
// \return      true          get line coding request processed.
// \return      false         get line coding request not supported or not processed.
bool USBD_CDCn_ACM_GetLineCoding (CDC_LINE_CODING *line_coding) {
  // Add code for get line coding
 
  return true;
}
 
 
// Called upon USB Host request to set control line states.
// \param [in]  state         control line settings bitmap.
//                - bit 0: DTR state
//                - bit 1: RTS state
// \return      true          set control line state request processed.
// \return      false         set control line state request not supported or not processed.
bool USBD_CDCn_ACM_SetControlLineState (uint16_t state) {
  // Add code for set control line state
 
  return true;
}