LibrePilot/flight/pios/stm32f4xx/pios_usb_cdc.c

/**
 ******************************************************************************
 * @addtogroup PIOS PIOS Core hardware abstraction layer
 * @{
 * @addtogroup   PIOS_USB_COM USB COM Functions
 * @brief PIOS USB COM implementation for CDC interfaces
 * @notes      This implements a CDC Serial Port
 * @{
 *
 * @file       pios_usb_com_cdc.c
 * @author     The OpenPilot Team, http://www.openpilot.org Copyright (C) 2010.
 * @brief      USB COM functions (STM32 dependent code)
 * @see        The GNU Public License (GPL) Version 3
 *
 *****************************************************************************/
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include "pios.h"

#ifdef PIOS_INCLUDE_USB_CDC

#include "pios_usb_cdc_priv.h"
#include "pios_usb_board_data.h" /* PIOS_BOARD_*_DATA_LENGTH */
#include "pios_usbhook.h"	 /* PIOS_USBHOOK_* */

/* Implement COM layer driver API */
static void PIOS_USB_CDC_RegisterTxCallback(uint32_t usbcdc_id, pios_com_callback tx_out_cb, uint32_t context);
static void PIOS_USB_CDC_RegisterRxCallback(uint32_t usbcdc_id, pios_com_callback rx_in_cb, uint32_t context);
static void PIOS_USB_CDC_TxStart(uint32_t usbcdc_id, uint16_t tx_bytes_avail);
static void PIOS_USB_CDC_RxStart(uint32_t usbcdc_id, uint16_t rx_bytes_avail);
static bool PIOS_USB_CDC_Available (uint32_t usbcdc_id);

const struct pios_com_driver pios_usb_cdc_com_driver = {
	.tx_start    = PIOS_USB_CDC_TxStart,
	.rx_start    = PIOS_USB_CDC_RxStart,
	.bind_tx_cb  = PIOS_USB_CDC_RegisterTxCallback,
	.bind_rx_cb  = PIOS_USB_CDC_RegisterRxCallback,
	.available   = PIOS_USB_CDC_Available,
};

enum pios_usb_cdc_dev_magic {
	PIOS_USB_CDC_DEV_MAGIC = 0xAABBCCDD,
};

struct pios_usb_cdc_dev {
	enum pios_usb_cdc_dev_magic     magic;
	const struct pios_usb_cdc_cfg * cfg;

	uint32_t lower_id;

	pios_com_callback rx_in_cb;
	uint32_t rx_in_context;
	pios_com_callback tx_out_cb;
	uint32_t tx_out_context;

	bool usb_ctrl_if_enabled;
	bool usb_data_if_enabled;

	uint8_t rx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH] __attribute__ ((aligned(4)));
	volatile bool rx_active;

	/*
	 * NOTE: This is -1 as somewhat of a hack.  It ensures that we always send packets
	 * that are strictly < maxPacketSize for this interface which means we never have
	 * to bother with zero length packets (ZLP).
	 */
	uint8_t tx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH - 1] __attribute__ ((aligned(4)));
	volatile bool tx_active;

	uint8_t ctrl_tx_packet_buffer[PIOS_USB_BOARD_CDC_MGMT_LENGTH] __attribute__ ((aligned(4)));

	uint32_t rx_dropped;
	uint32_t rx_oversize;

	/*
	 * Used to hold the current state of the simulated UART.  Changes to this 
	 * variable may trigger new USB CDC Notification packets to be sent to the host.
	 */
	volatile uint16_t prev_uart_state;
};

static bool PIOS_USB_CDC_validate(struct pios_usb_cdc_dev * usb_cdc_dev)
{
	return (usb_cdc_dev && (usb_cdc_dev->magic == PIOS_USB_CDC_DEV_MAGIC));
}

#if defined(PIOS_INCLUDE_FREERTOS)
static struct pios_usb_cdc_dev * PIOS_USB_CDC_alloc(void)
{
	struct pios_usb_cdc_dev * usb_cdc_dev;

	usb_cdc_dev = (struct pios_usb_cdc_dev *)pvPortMalloc(sizeof(*usb_cdc_dev));
	if (!usb_cdc_dev) return(NULL);

	memset(usb_cdc_dev, 0, sizeof(*usb_cdc_dev));
	usb_cdc_dev->magic = PIOS_USB_CDC_DEV_MAGIC;
	return(usb_cdc_dev);
}
#else
static struct pios_usb_cdc_dev pios_usb_cdc_devs[PIOS_USB_CDC_MAX_DEVS];
static uint8_t pios_usb_cdc_num_devs;
static struct pios_usb_cdc_dev * PIOS_USB_CDC_alloc(void)
{
	struct pios_usb_cdc_dev * usb_cdc_dev;

	if (pios_usb_cdc_num_devs >= PIOS_USB_CDC_MAX_DEVS) {
		return (NULL);
	}

	usb_cdc_dev = &pios_usb_cdc_devs[pios_usb_cdc_num_devs++];

	memset(usb_cdc_dev, 0, sizeof(*usb_cdc_dev));
	usb_cdc_dev->magic = PIOS_USB_CDC_DEV_MAGIC;

	return (usb_cdc_dev);
}
#endif

/* Implement USB_IFOPS for CDC Control Interface */
static void PIOS_USB_CDC_CTRL_IF_Init(uint32_t usb_cdc_id);
static void PIOS_USB_CDC_CTRL_IF_DeInit(uint32_t usb_cdc_id);
static bool PIOS_USB_CDC_CTRL_IF_Setup(uint32_t usb_cdc_id, struct usb_setup_request *req);
static void PIOS_USB_CDC_CTRL_IF_CtrlDataOut(uint32_t usb_cdc_id, const struct usb_setup_request *req);

static struct pios_usb_ifops usb_cdc_ctrl_ifops = {
	.init          = PIOS_USB_CDC_CTRL_IF_Init,
	.deinit        = PIOS_USB_CDC_CTRL_IF_DeInit,
	.setup         = PIOS_USB_CDC_CTRL_IF_Setup,
	.ctrl_data_out = PIOS_USB_CDC_CTRL_IF_CtrlDataOut,
};

/* Implement USB_IFOPS for CDC Data Interface */
static void PIOS_USB_CDC_DATA_IF_Init(uint32_t usb_cdc_id);
static void PIOS_USB_CDC_DATA_IF_DeInit(uint32_t usb_cdc_id);
static bool PIOS_USB_CDC_DATA_IF_Setup(uint32_t usb_cdc_id, struct usb_setup_request *req);
static void PIOS_USB_CDC_DATA_IF_CtrlDataOut(uint32_t usb_cdc_id, const struct usb_setup_request *req);

static struct pios_usb_ifops usb_cdc_data_ifops = {
	.init          = PIOS_USB_CDC_DATA_IF_Init,
	.deinit        = PIOS_USB_CDC_DATA_IF_DeInit,
	.setup         = PIOS_USB_CDC_DATA_IF_Setup,
	.ctrl_data_out = PIOS_USB_CDC_DATA_IF_CtrlDataOut,
};

static uint32_t pios_usb_cdc_id;

int32_t PIOS_USB_CDC_Init(uint32_t * usbcdc_id, const struct pios_usb_cdc_cfg * cfg, uint32_t lower_id)
{
	PIOS_Assert(usbcdc_id);
	PIOS_Assert(cfg);

	struct pios_usb_cdc_dev * usb_cdc_dev;

	usb_cdc_dev = (struct pios_usb_cdc_dev *) PIOS_USB_CDC_alloc();
	if (!usb_cdc_dev) goto out_fail;

	/* Bind the configuration to the device instance */
	usb_cdc_dev->cfg = cfg;
	usb_cdc_dev->lower_id = lower_id;

	pios_usb_cdc_id = (uint32_t) usb_cdc_dev;

	/* Rx and Tx are not active yet */
	usb_cdc_dev->rx_active = false;
	usb_cdc_dev->tx_active = false;

	/* Clear stats */
	usb_cdc_dev->rx_dropped = 0;
	usb_cdc_dev->rx_oversize = 0;

	/* Initialize the uart state */
	usb_cdc_dev->prev_uart_state = 0;

	/* Register class specific interface callbacks with the USBHOOK layer */
	usb_cdc_dev->usb_ctrl_if_enabled = false;
	PIOS_USBHOOK_RegisterIfOps(cfg->ctrl_if, &usb_cdc_ctrl_ifops, (uint32_t) usb_cdc_dev);

	/* Register class specific interface callbacks with the USBHOOK layer */
	usb_cdc_dev->usb_data_if_enabled = false;
	PIOS_USBHOOK_RegisterIfOps(cfg->data_if, &usb_cdc_data_ifops, (uint32_t) usb_cdc_dev);

	*usbcdc_id = (uint32_t) usb_cdc_dev;

	return 0;

out_fail:
	return -1;
}

static bool PIOS_USB_CDC_SendData(struct pios_usb_cdc_dev * usb_cdc_dev)
{
	uint16_t bytes_to_tx;

	if (!usb_cdc_dev->tx_out_cb) {
		return false;
	}

	bool need_yield = false;
	bytes_to_tx = (usb_cdc_dev->tx_out_cb)(usb_cdc_dev->tx_out_context,
					       usb_cdc_dev->tx_packet_buffer,
					       sizeof(usb_cdc_dev->tx_packet_buffer),
					       NULL,
					       &need_yield);
	if (bytes_to_tx == 0) {
		return false;
	}

	/* 
	 * Mark this endpoint as being tx active _before_ actually transmitting
	 * to make sure we don't race with the Tx completion interrupt
	 */
	usb_cdc_dev->tx_active = true;

	PIOS_USBHOOK_EndpointTx(usb_cdc_dev->cfg->data_tx_ep,
				usb_cdc_dev->tx_packet_buffer,
				bytes_to_tx);

#if defined(PIOS_INCLUDE_FREERTOS)
	if (need_yield) {
		vPortYieldFromISR();
	}
#endif	/* PIOS_INCLUDE_FREERTOS */

	return true;
}

static void PIOS_USB_CDC_RxStart(uint32_t usbcdc_id, uint16_t rx_bytes_avail) {
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usbcdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	/* Make sure this USB interface has been initialized */
	if (!usb_cdc_dev->usb_data_if_enabled) {
		return;
	}

	if (!PIOS_USB_CheckAvailable(usb_cdc_dev->lower_id)) {
		return;
	}

	// If endpoint was stalled and there is now space make it valid
	if (!usb_cdc_dev->rx_active && (rx_bytes_avail >= PIOS_USB_BOARD_CDC_DATA_LENGTH)) {
		PIOS_USBHOOK_EndpointRx(usb_cdc_dev->cfg->data_rx_ep,
					usb_cdc_dev->rx_packet_buffer,
					sizeof(usb_cdc_dev->rx_packet_buffer));
		usb_cdc_dev->rx_active = true;
	}
}

static void PIOS_USB_CDC_TxStart(uint32_t usbcdc_id, uint16_t tx_bytes_avail)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usbcdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	/* Make sure this USB interface has been initialized */
	if (!usb_cdc_dev->usb_data_if_enabled) {
		return;
	}

	if (!PIOS_USB_CheckAvailable(usb_cdc_dev->lower_id)) {
		return;
	}

	if (!usb_cdc_dev->tx_active) {
		/* Transmitter is not currently active, send a report */
		PIOS_USB_CDC_SendData(usb_cdc_dev);
	}
}

static void PIOS_USB_CDC_RegisterRxCallback(uint32_t usbcdc_id, pios_com_callback rx_in_cb, uint32_t context)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usbcdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	/* 
	 * Order is important in these assignments since ISR uses _cb
	 * field to determine if it's ok to dereference _cb and _context
	 */
	usb_cdc_dev->rx_in_context = context;
	usb_cdc_dev->rx_in_cb = rx_in_cb;
}

static void PIOS_USB_CDC_RegisterTxCallback(uint32_t usbcdc_id, pios_com_callback tx_out_cb, uint32_t context)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usbcdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	/* 
	 * Order is important in these assignments since ISR uses _cb
	 * field to determine if it's ok to dereference _cb and _context
	 */
	usb_cdc_dev->tx_out_context = context;
	usb_cdc_dev->tx_out_cb = tx_out_cb;
}

static bool PIOS_USB_CDC_CTRL_EP_IN_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len);

static void PIOS_USB_CDC_CTRL_IF_Init(uint32_t usb_cdc_id)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return;
	}

	/* Register endpoint specific callbacks with the USBHOOK layer */
	PIOS_USBHOOK_RegisterEpInCallback(usb_cdc_dev->cfg->ctrl_tx_ep,
					  sizeof(usb_cdc_dev->ctrl_tx_packet_buffer),
					  PIOS_USB_CDC_CTRL_EP_IN_Callback,
					  (uint32_t) usb_cdc_dev);
	usb_cdc_dev->usb_ctrl_if_enabled = true;
}

static void PIOS_USB_CDC_CTRL_IF_DeInit(uint32_t usb_cdc_id)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return;
	}

	/* DeRegister endpoint specific callbacks with the USBHOOK layer */
	usb_cdc_dev->usb_data_if_enabled = false;
}

static uint8_t cdc_altset;
static struct usb_cdc_line_coding line_coding = {
	.dwDTERate   = htousbl(57600),
	.bCharFormat = USB_CDC_LINE_CODING_STOP_1,
	.bParityType = USB_CDC_LINE_CODING_PARITY_NONE,
	.bDataBits   = 8,
};

static uint16_t control_line_state;

static bool PIOS_USB_CDC_CTRL_IF_Setup(uint32_t usb_cdc_id, struct usb_setup_request *req)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return false;
	}

	/* Make sure this is a request for an interface we know about */
	uint8_t ifnum = req->wIndex & 0xFF;
	if (ifnum != usb_cdc_dev->cfg->ctrl_if) {
		return (false);
	}

	switch (req->bmRequestType & (USB_REQ_TYPE_MASK | USB_REQ_RECIPIENT_MASK)) {
	case (USB_REQ_TYPE_STANDARD | USB_REQ_RECIPIENT_INTERFACE):
		switch (req->bRequest) {
		case USB_REQ_GET_INTERFACE:
			PIOS_USBHOOK_CtrlTx(&cdc_altset, 1);
			break;
		case USB_REQ_SET_INTERFACE:
			cdc_altset = (uint8_t)(req->wValue);
			break;
		default:
			/* Unhandled standard request */
			return false;
			break;
		}
		break;
	case (USB_REQ_TYPE_CLASS    | USB_REQ_RECIPIENT_INTERFACE):
		switch (req->bRequest) {
		case USB_CDC_REQ_SET_LINE_CODING:
			PIOS_USBHOOK_CtrlRx((uint8_t *)&line_coding, sizeof(line_coding));
			break;
		case USB_CDC_REQ_GET_LINE_CODING:
			PIOS_USBHOOK_CtrlTx((uint8_t *)&line_coding, sizeof(line_coding));
			break;
		case USB_CDC_REQ_SET_CONTROL_LINE_STATE:
			control_line_state = req->wValue;
			break;
		default:
			/* Unhandled class request */
			return false;
			break;
		}
		break;
	default:
		/* Unhandled request */
		return false;
	}

	return true;
}

static bool PIOS_USB_CDC_Available (uint32_t usbcdc_id)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usbcdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	return (PIOS_USB_CheckAvailable(usb_cdc_dev->lower_id) &&
		(control_line_state & USB_CDC_CONTROL_LINE_STATE_DTE_PRESENT));
}

/**
 * Called *after* the data has been written to the buffer provided in the setup stage.  The
 * setup request is passed in here again so we know *which* EP0 data out has just completed.
 */
static void PIOS_USB_CDC_CTRL_IF_CtrlDataOut(uint32_t usb_cdc_id, const struct usb_setup_request *req)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return;
	}

	/* Make sure this is a request for an interface we know about */
	uint8_t ifnum = req->wIndex & 0xFF;
	if (ifnum != usb_cdc_dev->cfg->ctrl_if) {
		return;
	}

	switch (req->bmRequestType & (USB_REQ_TYPE_MASK | USB_REQ_RECIPIENT_MASK)) {
	case (USB_REQ_TYPE_STANDARD | USB_REQ_RECIPIENT_INTERFACE):
		switch (req->bRequest) {
		default:
			/* Unhandled standard request */
			return;
			break;
		}
		break;
	case (USB_REQ_TYPE_CLASS    | USB_REQ_RECIPIENT_INTERFACE):
		switch (req->bRequest) {
		case USB_CDC_REQ_SET_LINE_CODING:
			/*
			 * If we cared to, this is where we would apply the new line coding
			 * that is now stored in the line_coding struct.  This could be used
			 * to notify the upper COM layer that the baud rate has changed.  This
			 * may be useful in the case of a COM USB bridge where we would
			 * auto-adjust the USART baud rate based on the line coding set here.
			 */
			break;
		default:
			/* Unhandled class request */
			return;
			break;
		}
		break;
	default:
		/* Unhandled request */
		return;
	}

	return;
}

static struct usb_cdc_serial_state_report uart_state = {
	.bmRequestType = 0xA1,
	.bNotification = USB_CDC_NOTIFICATION_SERIAL_STATE,
	.wValue        = 0,
	.wIndex        = htousbs(1),
	.wLength       = htousbs(2),
	.bmUartState   = htousbs(0),
};
	
static bool PIOS_USB_CDC_CTRL_EP_IN_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)pios_usb_cdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	/* Give back UART State Bitmap */
	/* UART State Bitmap
	 *   15-7: reserved
	 *      6:  bOverRun    overrun error
	 *      5:  bParity     parity error
	 *      4:  bFraming    framing error
	 *      3:  bRingSignal RI
	 *      2:  bBreak      break reception
	 *      1:  bTxCarrier  DSR
	 *      0:  bRxCarrier  DCD
	 */

	/* Currently, we only handle TxCarrier and RxCarrier reporting */
	uint16_t new_uart_state = 0;
	if (usb_cdc_dev->tx_out_cb) {
		/* Someone is going to providing FC->PC data, advertise an RxCarrier to the host */
		new_uart_state |= 0x1;
	}
	if (usb_cdc_dev->rx_in_cb) {
		/* Someone is consuming PC->FC data, advertise a TxCarrier to the host */
		new_uart_state |= 0x2;
	}

	/* Has anything changed since we last sent a notification? */
	if ((new_uart_state ^ usb_cdc_dev->prev_uart_state) & 0x3) {
		usb_cdc_dev->prev_uart_state = new_uart_state;

		uart_state.bmUartState = htousbs(new_uart_state);

		PIOS_USBHOOK_EndpointTx(usb_cdc_dev->cfg->ctrl_tx_ep,
					(uint8_t *)&uart_state,
					sizeof(uart_state));
	}

	return true;
}

static bool PIOS_USB_CDC_DATA_EP_IN_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len);
static bool PIOS_USB_CDC_DATA_EP_OUT_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len);

static void PIOS_USB_CDC_DATA_IF_Init(uint32_t usb_cdc_id)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return;
	}

	/* Register endpoint specific callbacks with the USBHOOK layer */
	PIOS_USBHOOK_RegisterEpInCallback(usb_cdc_dev->cfg->data_tx_ep,
					  sizeof(usb_cdc_dev->tx_packet_buffer),
					  PIOS_USB_CDC_DATA_EP_IN_Callback,
					  (uint32_t) usb_cdc_dev);
	PIOS_USBHOOK_RegisterEpOutCallback(usb_cdc_dev->cfg->data_rx_ep,
					   sizeof(usb_cdc_dev->rx_packet_buffer),
					   PIOS_USB_CDC_DATA_EP_OUT_Callback,
					   (uint32_t) usb_cdc_dev);
	usb_cdc_dev->usb_data_if_enabled = true;
}

static void PIOS_USB_CDC_DATA_IF_DeInit(uint32_t usb_cdc_id)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return;
	}

	/* DeRegister endpoint specific callbacks with the USBHOOK layer */
	usb_cdc_dev->usb_data_if_enabled = false;
	PIOS_USBHOOK_DeRegisterEpInCallback(usb_cdc_dev->cfg->data_tx_ep);
	PIOS_USBHOOK_DeRegisterEpOutCallback(usb_cdc_dev->cfg->data_rx_ep);
}

static bool PIOS_USB_CDC_DATA_IF_Setup(uint32_t usb_cdc_id, struct usb_setup_request *req)
{
	/* There are no valid EP0 transactions for CDC DATA interfaces */
	PIOS_Assert(0);

	return false;
}

/**
 * Called *after* the data has been written to the buffer provided in the setup stage.  The
 * setup request is passed in here again so we know *which* EP0 data out has just completed.
 */
static void PIOS_USB_CDC_DATA_IF_CtrlDataOut(uint32_t usb_cdc_id, const struct usb_setup_request *req)
{
	/* CDC DATA interfaces don't have any OUT data stages on the control endpoint */
	PIOS_Assert(0);
}

/**
 * @brief Callback used to indicate a transmission from device INto host completed
 * Checks if any data remains, pads it into HID packet and sends.
 */
static bool PIOS_USB_CDC_DATA_EP_IN_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)pios_usb_cdc_id;

	bool valid = PIOS_USB_CDC_validate(usb_cdc_dev);
	PIOS_Assert(valid);

	bool rc = PIOS_USB_CDC_SendData(usb_cdc_dev);
	if (!rc) {
		/* No additional data was transmitted, note that tx is no longer active */
		usb_cdc_dev->tx_active = false;
	}

	return rc;
}

static bool PIOS_USB_CDC_DATA_EP_OUT_Callback(uint32_t usb_cdc_id, uint8_t epnum, uint16_t len)
{
	struct pios_usb_cdc_dev * usb_cdc_dev = (struct pios_usb_cdc_dev *)pios_usb_cdc_id;

	if (!PIOS_USB_CDC_validate(usb_cdc_dev)) {
		return false;
	}

	if (len > sizeof(usb_cdc_dev->rx_packet_buffer)) {
		len = sizeof(usb_cdc_dev->rx_packet_buffer);
	}

	if (!usb_cdc_dev->rx_in_cb) {
		/* No Rx call back registered, disable the receiver */
		usb_cdc_dev->rx_active = false;
		return false;
	}

	uint16_t headroom;
	bool need_yield = false;
	uint16_t bytes_rxed;
	bytes_rxed = (usb_cdc_dev->rx_in_cb)(usb_cdc_dev->rx_in_context,
					usb_cdc_dev->rx_packet_buffer,
					len,
					&headroom,
					&need_yield);

	if (bytes_rxed < len) {
		/* Lost bytes on rx */
		usb_cdc_dev->rx_dropped += (len - bytes_rxed);
	}

	bool rc;
	if (headroom >= sizeof(usb_cdc_dev->rx_packet_buffer)) {
		/* We have room for a maximum length message */
		PIOS_USBHOOK_EndpointRx(usb_cdc_dev->cfg->data_rx_ep,
					usb_cdc_dev->rx_packet_buffer,
					sizeof(usb_cdc_dev->rx_packet_buffer));
		rc = true;
	} else {
		/* Not enough room left for a message, apply backpressure */
		usb_cdc_dev->rx_active = false;
		rc = false;
	}

#if defined(PIOS_INCLUDE_FREERTOS)
	if (need_yield) {
		vPortYieldFromISR();
	}
#endif	/* PIOS_INCLUDE_FREERTOS */

	return rc;
}

#endif /* PIOS_INCLUDE_USB_CDC */