dCDC_ACM Class Reference

USB CDC Abstract Control Model Device Class. More...

#include <usbd_cdc_acm.h>

Inherits nbrtos::USB::Device.

Public Member Functions
	dCDC_ACM (nbrtos::USB::Ctlr *parent, const usb_dev_t *desc, const usb_cfg_t *cfg, const nbrtos::USB::StrDescTbl *strTbl)
	Construct a CDC ACM device instance.
virtual void	Event_BusReset ()
	Handle USB bus reset event.
virtual void	Event_Suspend ()
	Handle USB suspend event.
virtual void	Event_Resume ()
	Handle USB resume event.
virtual int	Event_ControlMsg (nbrtos::USB::bufPtr_t ctlMsg, uint8_t bufLen)
	Handle USB control message.
virtual int	SetConfiguration (uint16_t wValue)
	Set the active USB configuration.
virtual int	SetAltSetting (uint16_t wIndex, uint16_t wValue)
	Set alternate interface setting.
virtual int	ProcessBuffer (uint8_t ep, PoolPtr pp, uint16_t bufLen)
	Process a received data buffer.
virtual uint16_t	GetStatus (eReqTarget_t target, uint16_t wIndex, int *err)
	Get device or endpoint status.
virtual uint8_t	GetActiveConfig (int *err)
	Get currently active configuration.
virtual uint8_t	GetAltSetting (uint8_t intfNum, int *err)
	Get current alternate setting for an interface.
virtual uint16_t	GetMaxPktSize (uint8_t epnum, eDir_t dir)
	Get maximum packet size for an endpoint.
nbrtos::USB::eBusState_t	GetUSBState ()
	Get current USB bus state.
void	SetUSBState (nbrtos::USB::eBusState_t newState)
	Set USB bus state.
int	ReadData (uint8_t *pData, int rdLen)
	Read data from the CDC device (non-blocking)
int	ReadWTimeout (uint8_t *pData, int rdLen, TickTimeout timeout)
	Read data from the CDC device with timeout.
int	WriteData (uint8_t *pData, int wrLen)
	Write data to the CDC device (non-blocking)
int	WriteWTimeout (uint8_t *pData, int wrLen, TickTimeout timeout)
	Write data to the CDC device with timeout.
int	Open ()
	Open the CDC device for use.
int	Peek (uint8_t *buf)
	Peek at the next byte without removing it.
virtual int	ProcessSetupPkt (uint8_t epnum, usb_setup_pkt_t msg)
	Process USB setup packet.

Static Public Member Functions
static int	sProcessBuffer (Device *dev, uint8_t ep, PoolPtr pp, uint16_t bufLen)
	Static callback wrapper for ProcessBuffer.

Detailed Description

USB CDC Abstract Control Model Device Class.

This class implements a USB CDC ACM device that provides virtual serial port functionality. When connected to a host computer, the device enumerates as a standard COM port, enabling serial communication over USB.

The class inherits from nbrtos::USB::Device and implements all required virtual functions for USB device operation, plus CDC-specific functionality for line coding and control signal management.

Key features:

• Buffered transmit and receive with FIFO storage
• File descriptor interface for standard I/O operations
• Configurable line parameters (baud, parity, stop bits, data bits)
• Event handling for USB bus states (reset, suspend, resume)
• Timeout-based read/write operations

Note

The device state machine handles USB enumeration automatically. Application code should use Open() to initialize the device and then use ReadData()/WriteData() or the file descriptor interface for data transfer.

---

Expand for Example Usage

Examples

Basic CDC ACM Device Setup

#include <predef.h>
#include <init.h>
#include <usbd_cdc_acm.h>
 
// USB descriptors (defined elsewhere)
extern const usb_dev_t myDeviceDesc;
extern const usb_cfg_t myConfigDesc;
extern const nbrtos::USB::StrDescTbl myStringTable;
 
dCDC_ACM *pCdcDevice = nullptr;
 
void UserMain(void *pd)
{
    init();
 
    // Get USB controller instance
    nbrtos::USB::Ctlr *pUsb = nbrtos::USB::GetController(0);
 
    // Create CDC ACM device
    pCdcDevice = new dCDC_ACM(pUsb, &myDeviceDesc, &myConfigDesc, &myStringTable);
 
    // Open the device for use
    int fd = pCdcDevice->Open();
    if (fd < 0)
    {
        iprintf("Failed to open CDC device\r\n");
    }
 
    // Main loop - echo received data
    uint8_t buffer[64];
    while (1)
    {
        int bytesRead = pCdcDevice->ReadWTimeout(buffer, sizeof(buffer),
                                                  TICKS_PER_SECOND);
        if (bytesRead > 0)
        {
            pCdcDevice->WriteData(buffer, bytesRead);
        }
    }
}

Reading Data with Timeout

void ProcessSerialData(dCDC_ACM *pCdc)
{
    uint8_t rxBuffer[256];
 
    // Wait up to 500ms for data
    int bytesRead = pCdc->ReadWTimeout(rxBuffer, sizeof(rxBuffer),
                                        TICKS_PER_SECOND / 2);
 
    if (bytesRead > 0)
    {
        iprintf("Received %d bytes\r\n", bytesRead);
        // Process received data...
    }
    else if (bytesRead == 0)
    {
        // Timeout - no data received
    }
    else
    {
        // Error occurred
        iprintf("Read error: %d\r\n", bytesRead);
    }
}

Checking USB Connection State

void MonitorUSBState(dCDC_ACM *pCdc)
{
    nbrtos::USB::eBusState_t state = pCdc->GetUSBState();
 
    switch (state)
    {
        case nbrtos::USB::eBusState_Configured:
            iprintf("USB configured and ready\r\n");
            break;
        case nbrtos::USB::eBusState_Suspended:
            iprintf("USB suspended\r\n");
            break;
        case nbrtos::USB::eBusState_Default:
            iprintf("USB in default state\r\n");
            break;
        default:
            iprintf("USB state: %d\r\n", (int)state);
            break;
    }
}

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Constructor & Destructor Documentation

dCDC_ACM()

dCDC_ACM::dCDC_ACM	(	nbrtos::USB::Ctlr *	parent,
		const usb_dev_t *	desc,
		const usb_cfg_t *	cfg,
		const nbrtos::USB::StrDescTbl *	strTbl )

Construct a CDC ACM device instance.

Creates a new CDC ACM device attached to the specified USB controller. The device will not be active until Open() is called.

Parameters

parent	Pointer to the USB controller this device is attached to
desc	Pointer to the USB device descriptor
cfg	Pointer to the USB configuration descriptor (includes CDC interface and endpoint descriptors)
strTbl	Pointer to the string descriptor table for device identification strings

Note

The descriptor pointers must remain valid for the lifetime of the device object.

Member Function Documentation

Event_BusReset()

virtual void dCDC_ACM::Event_BusReset ( )

virtual

Handle USB bus reset event.

Called by the USB stack when a bus reset is detected. Resets the device state machine and clears any pending transfers.

Event_ControlMsg()

virtual int dCDC_ACM::Event_ControlMsg ( nbrtos::USB::bufPtr_t ctlMsg, uint8_t bufLen )

virtual

Handle USB control message.

Processes control endpoint messages, including CDC-specific class requests such as GET_LINE_CODING, SET_LINE_CODING, and SET_CONTROL_LINE_STATE.

Parameters

ctlMsg	Pointer to the control message buffer
bufLen	Length of the control message

Returns

0 on success, or negative error code

Event_Resume()

virtual void dCDC_ACM::Event_Resume ( )

virtual

Handle USB resume event.

Called by the USB stack when the bus resumes from suspend state. Normal operation can continue after this event.

Event_Suspend()

virtual void dCDC_ACM::Event_Suspend ( )

virtual

Handle USB suspend event.

Called by the USB stack when the bus enters suspend state. The device should reduce power consumption when suspended.

GetActiveConfig()

virtual uint8_t dCDC_ACM::GetActiveConfig ( int * err )

virtual

Get currently active configuration.

Returns the current configuration value for GET_CONFIGURATION requests.

Parameters

[out]

err

Pointer to receive error code

Returns

Active configuration number (0 if not configured)

GetAltSetting()

virtual uint8_t dCDC_ACM::GetAltSetting ( uint8_t intfNum, int * err )

virtual

Get current alternate setting for an interface.

Returns the alternate setting for GET_INTERFACE requests.

Parameters

	intfNum	Interface number
[out]	err	Pointer to receive error code

Returns

Alternate setting value

GetMaxPktSize()

virtual uint16_t dCDC_ACM::GetMaxPktSize ( uint8_t epnum, eDir_t dir )

virtual

Get maximum packet size for an endpoint.

Returns the maximum packet size configured for the specified endpoint.

Parameters

epnum	Endpoint number
dir	Endpoint direction (IN or OUT)

Returns

Maximum packet size in bytes

GetStatus()

virtual uint16_t dCDC_ACM::GetStatus ( eReqTarget_t target, uint16_t wIndex, int * err )

virtual

Get device or endpoint status.

Returns the status for GET_STATUS requests.

Parameters

	target	Request target (device, interface, or endpoint)
	wIndex	Index value from the request (interface or endpoint number)
[out]	err	Pointer to receive error code

Returns

Status value, or 0 on error

GetUSBState()

nbrtos::USB::eBusState_t dCDC_ACM::GetUSBState

(

)

Get current USB bus state.

Returns the current state of the USB connection.

Returns

Current USB bus state (e.g., configured, suspended, default)

See also

SetUSBState()

Open()

int dCDC_ACM::Open

(

)

Open the CDC device for use.

Initializes the CDC device, sets up the file descriptor interface, and prepares the device for data transfer. Must be called before using ReadData(), WriteData(), or the file descriptor.

Returns

Non-negative file descriptor on success, or negative error code

Note

The returned file descriptor can be used with standard I/O functions like read(), write(), and close().

---

Expand for Example Usage

Examples

Opening and Using as File Descriptor

dCDC_ACM *pCdc;  // Previously created
 
int fd = pCdc->Open();
if (fd >= 0)
{
    // Can now use file descriptor I/O
    const char *msg = "Hello from NetBurner!\r\n";
    write(fd, msg, strlen(msg));
 
    // Or use the class methods directly
    pCdc->WriteData((uint8_t *)"Direct write\r\n", 14);
}

---

Peek()

int dCDC_ACM::Peek

(

uint8_t *

buf

)

Peek at the next byte without removing it.

Returns the next byte in the receive buffer without removing it. Useful for protocols that need to look ahead in the data stream.

Parameters

buf	Pointer to receive the peeked byte

Returns

1 if byte available, 0 if no data, or negative error code

ProcessBuffer()

virtual int dCDC_ACM::ProcessBuffer ( uint8_t ep, PoolPtr pp, uint16_t bufLen )

virtual

Process a received data buffer.

Called by the USB stack when data is received on an endpoint. Copies received data to the receive FIFO and signals waiting readers.

Parameters

ep	Endpoint number that received data
pp	Pool pointer to the received buffer
bufLen	Number of bytes received

Returns

0 on success, or negative error code

ProcessSetupPkt()

virtual int dCDC_ACM::ProcessSetupPkt ( uint8_t epnum, usb_setup_pkt_t msg )

virtual

Process USB setup packet.

Handles USB setup packets received on the control endpoint, including standard device requests and CDC class-specific requests.

Parameters

epnum	Endpoint number (typically 0 for control endpoint)
msg	USB setup packet to process

Returns

0 on success, or negative error code

ReadData()

int dCDC_ACM::ReadData	(	uint8_t *	pData,
		int	rdLen )

Read data from the CDC device (non-blocking)

Reads available data from the receive buffer. Returns immediately with whatever data is available, up to the requested length.

Parameters

pData	Pointer to buffer to receive data
rdLen	Maximum number of bytes to read

Returns

Number of bytes read (may be 0 if no data available), or negative error code

See also

ReadWTimeout() for blocking reads with timeout

ReadWTimeout()

int dCDC_ACM::ReadWTimeout	(	uint8_t *	pData,
		int	rdLen,
		TickTimeout	timeout )

Read data from the CDC device with timeout.

Reads data from the receive buffer, waiting up to the specified timeout for data to become available.

Parameters

pData	Pointer to buffer to receive data
rdLen	Maximum number of bytes to read
timeout	Maximum time to wait for data (in system ticks)

Returns

Number of bytes read, 0 on timeout, or negative error code

See also

ReadData() for non-blocking reads

---

Expand for Example Usage

Examples

Reading a Line with Timeout

int ReadLine(dCDC_ACM *pCdc, char *buffer, int maxLen, TickTimeout timeout)
{
    int index = 0;
    uint8_t ch;
 
    while (index < (maxLen - 1))
    {
        int result = pCdc->ReadWTimeout(&ch, 1, timeout);
        if (result <= 0)
        {
            break;  // Timeout or error
        }
 
        if (ch == '\n')
        {
            break;  // End of line
        }
 
        if (ch != '\r')
        {
            buffer[index++] = (char)ch;
        }
    }
 
    buffer[index] = '\0';
    return index;
}

---

SetAltSetting()

virtual int dCDC_ACM::SetAltSetting ( uint16_t wIndex, uint16_t wValue )

virtual

Set alternate interface setting.

Called by the USB stack when the host selects an alternate setting for an interface.

Parameters

wIndex	Interface number
wValue	Alternate setting value

Returns

0 on success, or negative error code

SetConfiguration()

virtual int dCDC_ACM::SetConfiguration ( uint16_t wValue )

virtual

Set the active USB configuration.

Called by the USB stack when the host selects a configuration. Initializes endpoints and prepares the device for data transfer.

Parameters

wValue

Configuration value from SET_CONFIGURATION request

Returns

0 on success, or negative error code

SetUSBState()

void dCDC_ACM::SetUSBState

(

nbrtos::USB::eBusState_t

newState

)

Set USB bus state.

Updates the internal USB state. Typically called by event handlers.

Parameters

newState

New USB bus state to set

See also

GetUSBState()

sProcessBuffer()

static int dCDC_ACM::sProcessBuffer ( Device * dev, uint8_t ep, PoolPtr pp, uint16_t bufLen )

static

Static callback wrapper for ProcessBuffer.

Static member function that dispatches to the instance ProcessBuffer method. Used for registering with the USB stack callback system.

Parameters

dev	Pointer to the device instance
ep	Endpoint number
pp	Pool pointer to the buffer
bufLen	Buffer length

Returns

Result from ProcessBuffer()

WriteData()

int dCDC_ACM::WriteData	(	uint8_t *	pData,
		int	wrLen )

Write data to the CDC device (non-blocking)

Writes data to the transmit buffer. Returns immediately after copying data to the buffer. The actual USB transmission occurs asynchronously.

Parameters

pData	Pointer to data to write
wrLen	Number of bytes to write

Returns

Number of bytes written (may be less than requested if buffer space is limited), or negative error code

See also

WriteWTimeout() for blocking writes with timeout

WriteWTimeout()

int dCDC_ACM::WriteWTimeout	(	uint8_t *	pData,
		int	wrLen,
		TickTimeout	timeout )

Write data to the CDC device with timeout.

Writes data to the transmit buffer, waiting up to the specified timeout for buffer space to become available.

Parameters

pData	Pointer to data to write
wrLen	Number of bytes to write
timeout	Maximum time to wait for buffer space (in system ticks)

Returns

Number of bytes written, 0 on timeout, or negative error code

See also

WriteData() for non-blocking writes

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The documentation for this class was generated from the following file:

• usbd_cdc_acm.h