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nuttx/include/nuttx/can.h
Gregory Nutt 815ec07b55 CAN: A minor improvement to can_txready design
2015-11-15 06:36:30 -06:00

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/************************************************************************************
* include/nuttx/can.h
*
* Copyright (C) 2008, 2009, 2011-2012, 2015 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
************************************************************************************/
#ifndef _INCLUDE_NUTTX_CAN_H
#define _INCLUDE_NUTTX_CAN_H
/************************************************************************************
* Included Files
************************************************************************************/
#include <nuttx/config.h>
#include <nuttx/compiler.h>
#include <sys/types.h>
#include <stdint.h>
#include <stdbool.h>
#include <semaphore.h>
#include <nuttx/fs/fs.h>
#include <nuttx/fs/ioctl.h>
#ifdef CONFIG_CAN_TXREADY
# include <nuttx/wqueue.h>
#endif
#ifdef CONFIG_CAN
/************************************************************************************
* Pre-processor Definitions
************************************************************************************/
/* Configuration ********************************************************************/
/* CONFIG_CAN - Enables CAN support (one or both of CONFIG_STM32_CAN1 or
* CONFIG_STM32_CAN2 must also be defined)
* CONFIG_CAN_EXTID - Enables support for the 29-bit extended ID. Default
* Standard 11-bit IDs.
* CONFIG_CAN_FD - Enable support for CAN FD mode. For the upper half driver, this
* just means handling encoded DLC values (for values of DLC > 9).
* CONFIG_CAN_FIFOSIZE - The size of the circular buffer of CAN messages.
* Default: 8
* CONFIG_CAN_NPENDINGRTR - The size of the list of pending RTR requests.
* Default: 4
* CONFIG_CAN_LOOPBACK - A CAN driver may or may not support a loopback
* mode for testing. If the driver does support loopback mode, the setting
* will enable it. (If the driver does not, this setting will have no effect).
* CONFIG_CAN_TXREADY - Add support for the can_txready() callback. This is needed
* only for CAN hardware the supports an separate H/W TX message FIFO. The call
* back is needed to keep the S/W FIFO and the H/W FIFO in sync. Work queue
* support is needed for this feature.
* CONFIG_CAN_TXREADY_HIPRI or CONFIG_CAN_TXREADY_LOPRI - Selects which work queue
* will be used for the can_txready() processing.
*/
/* Default configuration settings that may be overridden in the NuttX configuration
* file or in the board configuration file. The configured size is limited to 255
* to fit into a uint8_t.
*/
#if !defined(CONFIG_CAN_FIFOSIZE)
# define CONFIG_CAN_FIFOSIZE 8
#elif CONFIG_CAN_FIFOSIZE > 255
# undef CONFIG_CAN_FIFOSIZE
# define CONFIG_CAN_FIFOSIZE 255
#endif
#if !defined(CONFIG_CAN_NPENDINGRTR)
# define CONFIG_CAN_NPENDINGRTR 4
#elif CONFIG_CAN_NPENDINGRTR > 255
# undef CONFIG_CAN_NPENDINGRTR
# define CONFIG_CAN_NPENDINGRTR 255
#endif
/* Ioctl Commands *******************************************************************/
/* Ioctl commands supported by the upper half CAN driver.
*
* CANIOC_RTR:
* Description: Send the remote transmission request and wait for the response.
* Argument: A reference to struct canioc_rtr_s
*
* Ioctl commands that may or may not be supported by the lower half CAN driver.
*
* CANIOC_ADD_STDFILTER:
* Description: Add an address filter for a standard 11 bit address.
* Argument: A reference to struct canioc_stdfilter_s
* Returned Value: A non-negative filter ID is returned on success.
* Otherwise -1 (ERROR) is returned with the errno
* variable set to indicate the nature of the error.
* Dependencies: None
*
* CANIOC_ADD_EXTFILTER:
* Description: Add an address filter for a extended 29 bit address.
* Argument: A reference to struct canioc_extfilter_s
* Returned Value: A non-negative filter ID is returned on success.
* Otherwise -1 (ERROR) is returned with the errno
* variable set to indicate the nature of the error.
* Dependencies: Requires CONFIG_CAN_EXTID=y
*
* CANIOC_DEL_STDFILTER:
* Description: Remove an address filter for a standard 11 bit address.
* Argument: The filter index previously returned by the
* CANIOC_ADD_STDFILTER command
* Returned Value: Zero (OK) is returned on success. Otherwise -1 (ERROR)
* is returned with the errno variable set to indicate the
* nature of the error.
* Dependencies: None
*
* CANIOC_DEL_EXTFILTER:
* Description: Remove an address filter for a standard 29 bit address.
* Argument: The filter index previously returned by the
* CANIOC_ADD_EXTFILTER command
* Returned Value: Zero (OK) is returned on success. Otherwise -1 (ERROR)
* is returned with the errno variable set to indicate the
* nature of the error.
* Dependencies: Requires CONFIG_CAN_EXTID=y
*
* CANIOC_GET_BITTIMING:
* Description: Return the current bit timing settings
* Argument: A pointer to a write-able instance of struct
* canioc_bittiming_s in which current bit timing values
* will be returned.
* Returned Value: Zero (OK) is returned on success. Otherwise -1 (ERROR)
* is returned with the errno variable set to indicate the
* nature of the error.
* Dependencies: None
*
* CANIOC_SET_BITTIMING:
* Description: Set new current bit timing values
* Argument: A pointer to a read-able instance of struct
* canioc_bittiming_s in which the new bit timing values
* are provided.
* Returned Value: Zero (OK) is returned on success. Otherwise -1 (ERROR)
* is returned with the errno variable set to indicate the
* nature of the error.
* Dependencies: None
*/
#define CANIOC_RTR _CANIOC(1)
#define CANIOC_GET_BITTIMING _CANIOC(2)
#define CANIOC_SET_BITTIMING _CANIOC(3)
#define CANIOC_ADD_STDFILTER _CANIOC(4)
#define CANIOC_ADD_EXTFILTER _CANIOC(5)
#define CANIOC_DEL_STDFILTER _CANIOC(6)
#define CANIOC_DEL_EXTFILTER _CANIOC(7)
/* CANIOC_USER: Device specific ioctl calls can be supported with cmds greater
* than this value
*/
#define CANIOC_USER _CANIOC(8)
/* Convenience macros ***************************************************************/
#define dev_reset(dev) dev->cd_ops->co_reset(dev)
#define dev_setup(dev) dev->cd_ops->co_setup(dev)
#define dev_shutdown(dev) dev->cd_ops->co_shutdown(dev)
#define dev_txint(dev,enable) dev->cd_ops->co_txint(dev,enable)
#define dev_rxint(dev,enable) dev->cd_ops->co_rxint(dev,enable)
#define dev_ioctl(dev,cmd,arg) dev->cd_ops->co_ioctl(dev,cmd,arg)
#define dev_remoterequest(dev,id) dev->cd_ops->co_remoterequest(dev,id)
#define dev_send(dev,m) dev->cd_ops->co_send(dev,m)
#define dev_txready(dev) dev->cd_ops->co_txready(dev)
#define dev_txempty(dev) dev->cd_ops->co_txempty(dev)
/* CAN message support **************************************************************/
#ifdef CONFIG_CAN_FD
# define CAN_MAXDATALEN 64
#else
# define CAN_MAXDATALEN 8
#endif
#define CAN_MAX_STDMSGID 0x07ff
#define CAN_MAX_EXTMSGID 0x1fffffff
#define CAN_MSGLEN(nbytes) (sizeof(struct can_msg_s) - CAN_MAXDATALEN + (nbytes))
/* CAN Error Indications ************************************************************/
#define CAN_ERROR_SYSTEM (1 << 0) /* Bit 0: Driver internal error */
#define CAN_ERROR_RXLOST (1 << 1) /* Bit 1: RX Message Lost */
#define CAN_ERROR_TXLOST (1 << 2) /* Bit 2: TX Message Lost */
#define CAN_ERROR_ACCESS (1 << 3) /* Bit 3: RAM Access Failure */
#define CAN_ERROR_TIMEOUT (1 << 4) /* Bit 4: Timeout Occurred */
#define CAN_ERROR_PASSIVE (1 << 5) /* Bit 5: Error Passive */
#define CAN_ERROR_CRC (1 << 6) /* Bit 6: RX CRC Error */
#define CAN_ERROR_BIT (1 << 7) /* Bit 7: Bit Error */
#define CAN_ERROR_ACK (1 << 8) /* Bit 8: Acknowledge Error */
#define CAN_ERROR_FORMAT (1 << 9) /* Bit 9: Format Error */
#define CAN_ERROR_STUFF (1 << 10) /* Bit 10: Stuff Error */
#define CAN_ERROR_ALL (0x07ff)
/* CAN filter support ***************************************************************/
/* Some CAN hardware supports a notion of prioritizing messages that match filters.
* Only two priority levels are currently supported and are encoded as defined
* below:
*/
#define CAN_MSGPRIO_LOW 0
#define CAN_MSGPRIO_HIGH 1
/* Filter type. Not all CAN hardware will support all filter types. */
#define CAN_FILTER_MASK 0 /* Address match under a mask */
#define CAN_FILTER_DUAL 1 /* Dual address match */
#define CAN_FILTER_RANGE 2 /* Match a range of addresses */
/************************************************************************************
* Public Types
************************************************************************************/
/* CAN-message Format (without Extended ID support)
*
* One based CAN-message is represented with a maximum of 10 bytes. A message is
* composed of at least the first 2 bytes (when there are no data bytes present).
*
* Bytes 0-1: Bits 0-3: Data Length Code (DLC)
* Bit 4: Remote Transmission Request (RTR)
* Bit 5: 1=Message ID is a bit-encoded error report (See NOTE)
* Bits 6-7: Unused
* Bytes 1-2: Bits 0-10: The 11-bit CAN identifier This message ID is a bit
* encoded error set if ch_error is set (See NOTE).
* Bits 11-15: Unused
* Bytes 3-10: CAN data
*
* CAN-message Format (with Extended ID support)
*
* One CAN-message consists of a maximum of 13 bytes. A message is composed of at
* least the first 5 bytes (when there are no data bytes).
*
* Bytes 0-3: Bits 0-28: Hold 11- or 29-bit CAN ID in host byte order. This
* message ID is a bit encoded error set if ch_error
* is set (See NOTE).
* Bits 29-31: Unused
* Byte 4: Bits 0-3: Data Length Code (DLC)
* Bit 4: Remote Transmission Request (RTR)
* Bit 5: 1=Message ID is a bit-encoded error report (See NOTE)
* Bit 6: Extended ID indication
* Bit 7: Unused
* Bytes 5-12: CAN data Size determined by DLC
*
* NOTE: The error indication if valid only on message reports received from the
* CAN driver; it is ignored on transmission. When the error bit is set, the
* message ID is an encoded set of error indications (see CAN_ERROR_* definitions).
*
* The struct can_msg_s holds this information in a user-friendly, unpacked form.
* This is the form that is used at the read() and write() driver interfaces. The
* message structure is actually variable length -- the true length is given by
* the CAN_MSGLEN macro.
*/
#ifdef CONFIG_CAN_EXTID
struct can_hdr_s
{
uint32_t ch_id; /* 11- or 29-bit ID (20- or 3-bits unused) */
uint8_t ch_dlc : 4; /* 4-bit DLC */
uint8_t ch_rtr : 1; /* RTR indication */
uint8_t ch_error : 1; /* 1=ch_id is an error report */
uint8_t ch_extid : 1; /* Extended ID indication */
uint8_t ch_unused : 1; /* Unused */
} packed_struct;
#else
struct can_hdr_s
{
uint16_t ch_id; /* 11-bit standard ID (5-bits unused) */
uint8_t ch_dlc : 4; /* 4-bit DLC. May be encoded in CAN_FD mode. */
uint8_t ch_rtr : 1; /* RTR indication */
uint8_t ch_error : 1; /* 1=ch_id is an error report */
uint8_t ch_unused : 2; /* Unused */
} packed_struct;
#endif
struct can_msg_s
{
struct can_hdr_s cm_hdr; /* The CAN header */
uint8_t cm_data[CAN_MAXDATALEN]; /* CAN message data (0-8 byte) */
} packed_struct;
/* This structure defines a CAN message FIFO. */
struct can_rxfifo_s
{
sem_t rx_sem; /* Counting semaphore */
uint8_t rx_head; /* Index to the head [IN] in the circular buffer */
uint8_t rx_tail; /* Index to the tail [OUT] in the circular buffer */
/* Circular buffer of CAN messages */
struct can_msg_s rx_buffer[CONFIG_CAN_FIFOSIZE];
};
struct can_txfifo_s
{
sem_t tx_sem; /* Counting semaphore */
uint8_t tx_head; /* Index to the head [IN] in the circular buffer */
uint8_t tx_queue; /* Index to next message to send */
uint8_t tx_tail; /* Index to the tail [OUT] in the circular buffer */
/* Circular buffer of CAN messages */
struct can_msg_s tx_buffer[CONFIG_CAN_FIFOSIZE];
};
/* The following structure define the logic to handle one RTR message transaction */
struct can_rtrwait_s
{
sem_t cr_sem; /* Wait for RTR response */
uint16_t cr_id; /* The ID that is waited for */
FAR struct can_msg_s *cr_msg; /* This is where the RTR response goes */
};
/* This structure defines all of the operations provided by the architecture specific
* logic. All fields must be provided with non-NULL function pointers by the
* caller of can_register().
*/
struct can_dev_s;
struct can_ops_s
{
/* Reset the CAN device. Called early to initialize the hardware. This
* is called, before co_setup() and on error conditions.
*/
CODE void (*co_reset)(FAR struct can_dev_s *dev);
/* Configure the CAN. This method is called the first time that the CAN
* device is opened. This will occur when the port is first opened.
* This setup includes configuring and attaching CAN interrupts. All CAN
* interrupts are disabled upon return.
*/
CODE int (*co_setup)(FAR struct can_dev_s *dev);
/* Disable the CAN. This method is called when the CAN device is closed.
* This method reverses the operation the setup method.
*/
CODE void (*co_shutdown)(FAR struct can_dev_s *dev);
/* Call to enable or disable RX interrupts */
CODE void (*co_rxint)(FAR struct can_dev_s *dev, bool enable);
/* Call to enable or disable TX interrupts */
CODE void (*co_txint)(FAR struct can_dev_s *dev, bool enable);
/* All ioctl calls will be routed through this method */
CODE int (*co_ioctl)(FAR struct can_dev_s *dev, int cmd, unsigned long arg);
/* Send a remote request */
CODE int (*co_remoterequest)(FAR struct can_dev_s *dev, uint16_t id);
/* This method will send one message on the CAN */
CODE int (*co_send)(FAR struct can_dev_s *dev, FAR struct can_msg_s *msg);
/* Return true if the CAN hardware can accept another TX message. */
CODE bool (*co_txready)(FAR struct can_dev_s *dev);
/* Return true if all message have been sent. If for example, the CAN
* hardware implements FIFOs, then this would mean the transmit FIFO is
* empty. This method is called when the driver needs to make sure that
* all characters are "drained" from the TX hardware before calling co_shutdown().
*/
CODE bool (*co_txempty)(FAR struct can_dev_s *dev);
};
/* This is the device structure used by the driver. The caller of
* can_register() must allocate and initialize this structure. The
* calling logic need only set all fields to zero except:
*
* The elements of 'cd_ops', and 'cd_priv'
*
* The common logic will initialize all semaphores.
*/
struct can_dev_s
{
uint8_t cd_ocount; /* The number of times the device has been opened */
uint8_t cd_npendrtr; /* Number of pending RTR messages */
volatile uint8_t cd_ntxwaiters; /* Number of threads waiting to enqueue a message */
volatile uint8_t cd_nrxwaiters; /* Number of threads waiting to receive a message */
sem_t cd_closesem; /* Locks out new opens while close is in progress */
struct can_txfifo_s cd_xmit; /* Describes transmit FIFO */
struct can_rxfifo_s cd_recv; /* Describes receive FIFO */
#ifdef CONFIG_CAN_TXREADY
struct work_s cd_work; /* Use to manage can_txready() work */
#endif
/* List of pending RTR requests */
struct can_rtrwait_s cd_rtr[CONFIG_CAN_NPENDINGRTR];
FAR const struct can_ops_s *cd_ops; /* Arch-specific operations */
FAR void *cd_priv; /* Used by the arch-specific logic */
};
/* Structures used with ioctl calls */
/* CANIOC_RTR: */
struct canioc_rtr_s
{
uint16_t ci_id; /* The 11-bit ID to use in the RTR message */
FAR struct can_msg_s *ci_msg; /* The location to return the RTR response */
};
/* CANIOC_GET_BITTIMING/CANIOC_SET_BITTIMING: */
/* Bit time = Tquanta * (Sync_Seg + Prop_Seq + Phase_Seg1 + Phase_Seg2)
* = Tquanta * (TSEG1 + TSEG2 + 1)
* Where
* TSEG1 = Prop_Seq + Phase_Seg1
* TSEG2 = Phase_Seg2
*/
struct canioc_bittiming_s
{
uint32_t bt_baud; /* Bit rate = 1 / bit time */
uint8_t bt_tseg1; /* TSEG1 in time quanta */
uint8_t bt_tseg2; /* TSEG2 in time quanta */
uint8_t bt_sjw; /* Synchronization Jump Width in time quanta */
};
#ifdef CONFIG_CAN_EXTID
/* CANIOC_ADD_EXTFILTER: */
struct canioc_extfilter_s
{
uint32_t xf_id1; /* 29-bit ID. For dual match or for the
* lower address in a range of addresses */
uint32_t xf_id2; /* 29-bit ID. For dual match, address mask
* or for upper address in address range */
uint8_t xf_type; /* See CAN_FILTER_* definitions */
uint8_t xf_prio; /* See CAN_MSGPRIO_* definitions */
};
#endif
/* CANIOC_ADD_STDFILTER: */
struct canioc_stdfilter_s
{
uint16_t sf_id1; /* 11-bit ID. For dual match or for the
* lower address in a range of addresses */
uint16_t sf_id2; /* 11-bit ID. For dual match, address mask
* or for upper address in address range */
uint8_t sf_type; /* See CAN_FILTER_* definitions */
uint8_t sf_prio; /* See CAN_MSGPRIO_* definitions */
};
/************************************************************************************
* Public Data
************************************************************************************/
/************************************************************************************
* Public Functions
************************************************************************************/
#undef EXTERN
#if defined(__cplusplus)
#define EXTERN extern "C"
extern "C"
{
#else
#define EXTERN extern
#endif
/************************************************************************************
* Name: can_register
*
* Description:
* Register a CAN driver.
*
************************************************************************************/
int can_register(FAR const char *path, FAR struct can_dev_s *dev);
/************************************************************************************
* Name: can_receive
*
* Description:
* Called from the CAN interrupt handler when new read data is available
*
* Input Parameters:
* dev - The specific CAN device
* hdr - The 16-bit CAN header
* data - An array contain the CAN data.
*
* Returned Value:
* OK on success; a negated errno on failure.
*
************************************************************************************/
int can_receive(FAR struct can_dev_s *dev, FAR struct can_hdr_s *hdr,
FAR uint8_t *data);
/************************************************************************************
* Name: can_txdone
*
* Description:
* Called when the hardware has processed the outgoing TX message. This
* normally means that the CAN messages was sent out on the wire. But
* if the CAN hardware supports a H/W TX FIFO, then this call may mean
* only that the CAN message has been added to the H/W FIFO. In either
* case, the upper-half CAN driver can remove the outgoing message from
* the S/W FIFO and discard it.
*
* This function may be called in different contexts, depending upon the
* nature of the underlying CAN hardware.
*
* 1. No H/W TX FIFO (CONFIG_CAN_TXREADY not defined)
*
* This function is only called from the CAN interrupt handler at the
* completion of a send operation.
*
* can_write() -> can_xmit() -> dev_send()
* CAN interrupt -> can_txdone()
*
* If the CAN hardware is busy, then the call to dev_send() will
* fail, the S/W TX FIFO will accumulate outgoing messages, and the
* thread calling can_write() may eventually block waiting for space in
* the S/W TX FIFO.
*
* When the CAN hardware completes the transfer and processes the
* CAN interrupt, the call to can_txdone() will make space in the S/W
* TX FIFO and will awaken the waiting can_write() thread.
*
* 2a. H/W TX FIFO (CONFIG_CAN_TXREADY=y) and S/W TX FIFO not full
*
* This function will be called back from dev_send() immediately when a
* new CAN message is added to H/W TX FIFO:
*
* can_write() -> can_xmit() -> dev_send() -> can_txdone()
*
* When the H/W TX FIFO becomes full, dev_send() will fail and
* can_txdone() will not be called. In this case the S/W TX FIFO will
* accumulate outgoing messages, and the thread calling can_write() may
* eventually block waiting for space in the S/W TX FIFO.
*
* 2b. H/W TX FIFO (CONFIG_CAN_TXREADY=y) and S/W TX FIFO full
*
* In this case, the thread calling can_write() is blocked waiting for
* space in the S/W TX FIFO. can_txdone() will be called, indirectly,
* from can_txready_work() running on the thread of the work queue.
*
* CAN interrupt -> can_txready() -> Schedule can_txready_work()
* can_txready_work() -> can_xmit() -> dev_send() -> can_txdone()
*
* The call dev_send() should not fail in this case and the subsequent
* call to can_txdone() will make space in the S/W TX FIFO and will
* awaken the waiting thread.
*
* Input Parameters:
* dev - The specific CAN device
* hdr - The 16-bit CAN header
* data - An array contain the CAN data.
*
* Returned Value:
* OK on success; a negated errno on failure.
*
* Assumptions:
* Interrupts are disabled. This is required by can_xmit() which is called
* by this function. Interrupts are explicitly disabled when called
* through can_write(). Interrupts are expected be disabled when called
* from the CAN interrupt handler.
*
************************************************************************************/
int can_txdone(FAR struct can_dev_s *dev);
/************************************************************************************
* Name: can_txready
*
* Description:
* Called from the CAN interrupt handler at the completion of a send
* operation. This interface is needed only for CAN hardware that
* supports queing of outgoing messages in a H/W FIFO.
*
* The CAN upper half driver also supports a queue of output messages in a
* S/W FIFO. Messages are added to that queue when when can_write() is
* called and removed from the queue in can_txdone() when each TX message
* is complete.
*
* After each message is added to the S/W FIFO, the CAN upper half driver
* will attempt to send the message by calling into the lower half driver.
* That send will not be performed if the lower half driver is busy, i.e.,
* if dev_txready() returns false. In that case, the number of messages in
* the S/W FIFO can grow. If the S/W FIFO becomes full, then can_write()
* will wait for space in the S/W FIFO.
*
* If the CAN hardware does not support a H/W FIFO then busy means that
* the hardware is actively sending the message and is guaranteed to
* become non-busy (i.e, dev_txready()) when the send transfer completes
* and can_txdone() is called. So the call to can_txdone() means that the
* transfer has completed and also that the hardware is ready to accept
* another transfer.
*
* If the CAN hardware supports a H/W FIFO, can_txdone() is not called
* when the tranfer is complete, but rather when the transfer is queued in
* the H/W FIFO. When the H/W FIFO becomes full, then dev_txready() will
* report false and the number of queued messages in the S/W FIFO will grow.
*
* There is no mechanism in this case to inform the upper half driver when
* the hardware is again available, when there is again space in the H/W
* FIFO. can_txdone() will not be called again. If the S/W FIFO becomes
* full, then the upper half driver will wait for space to become
* available, but there is no event to awaken it and the driver will hang.
*
* Enabling this feature adds support for the can_txready() interface.
* This function is called from the lower half driver's CAN interrupt
* handler each time a TX transfer completes. This is a sure indication
* that the H/W FIFO is no longer full. can_txready() will then awaken
* the can_write() logic and the hang condition is avoided.
*
* Input Parameters:
* dev - The specific CAN device
*
* Returned Value:
* OK on success; a negated errno on failure.
*
* Assumptions:
* Interrupts are disabled. This function may execute in the context of
* and interrupt handler.
*
************************************************************************************/
#ifdef CONFIG_CAN_TXREADY
int can_txready(FAR struct can_dev_s *dev);
#endif
#undef EXTERN
#if defined(__cplusplus)
}
#endif
#endif /* CONFIG_CAN */
#endif /* _INCLUDE_NUTTX_CAN_H */
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