API Details

cyg_io_write

cyg_io_write(handle, buf, len)

To transmit a message an application must fill a cyg_can_message buffer and call cyg_io_write(). This function sends one single CAN message (not a buffer of CAN messages) to a device. The size of data to send is contained in *len and the actual size sent will be returned in the same place. A pointer to a cyg_can_message is contained in *buf. The driver maintains a buffer to hold the data. The size of the intermediate buffer is configurable within the interface module. The data is not modified at all while it is being buffered. On return, *len contains the amount of characters actually consumed - that means *len always contains sizeof(cyg_can_message).

It is possible to configure the write call to be blocking (default) or non-blocking. Non-blocking mode requires both the configuration option CYGOPT_IO_CAN_SUPPORT_NONBLOCKING to be enabled, and the specific device to be set to non-blocking mode for writes (see cyg_io_set_config()). In blocking mode, the call will not return until there is space in the buffer and the content of the CAN message has been consumed. In non-blocking mode, if there is no space in buffer for the CAN message, -EAGAIN is returned and the caller must try again.

It is possible to configure the write call to be non-blocking with timeout. None-blocking mode with timeout requires the configuration option CYGOPT_IO_CAN_SUPPORT_NONBLOCKING and CYGOPT_IO_CAN_SUPPORT_TIMEOUTS to be enabled, requires the eCos kernel package to be included and the specific device to be set to non-blocking mode for writes (see cyg_io_set_config()). In non-blocking mode with timeouts, if there is no space in buffer for the CAN message, the driver waits a certain amount of time (the timeout time) for space in the buffer. If there is still no space in buffer after expiration of the timeout time, -EINTR is returned and the caller must try again.

If a message was successfully sent, the function returns ENOERR.

CAN Messages

The CAN driver uses cyg_can_message structures to pass messages between the application and the CAN driver. The type cyg_can_message provides a device independent type of CAN message. Before calling the write function this message should be setup properly.

typedef struct can_message
{
    cyg_uint32         id;
    cyg_uint8          data[8];
    cyg_can_id_type    ext;
    cyg_can_frame_type rtr;
    cyg_uint8          dlc;
} cyg_can_message;

The structure contains the following fields:

Example code for sending one single CAN message:

cyg_can_message tx_msg;
cyg_uint32      len;
Cyg_ErrNo       ret;

tx_msg.id  = 0x100;
tx_msg.ext = CYGNUM_CAN_ID_EXT;
tx_msg.rtr = CYGNUM_CAN_FRAME_DATA;
tx_msg.dlc = 1;
tx_msg.data[0] = 0xF1;

len = sizeof(tx_msg);
ret = cyg_io_write(hDrvCAN, &tx_msg, &len);

cyg_io_read

cyg_io_read(handle, buf, len)

To receive a message the application calls cyg_io_read(). This function receives one single event from a device. The desired size of data to receive is contained in *len and the actual size obtained will be returned in the same place. A pointer to a cyg_can_event is contained in *buf. No manipulation of the data is performed before being transferred. Again, this buffering is completely configurable. On return, *len contains sizeof(cyg_can_event).

It is possible to configure the read call to be blocking (default) or non-blocking. Non-blocking mode requires both the configuration option CYGOPT_IO_CAN_SUPPORT_NONBLOCKING to be enabled, and the specific device to be set to non-blocking mode for reads (see cyg_io_set_config()). In blocking mode, the call will not return until one single CAN event has been read. In non-blocking mode, if there is no CAN event in buffer, the call returns immediately with -EAGAIN and the caller must try again.

It is possible to configure the read call to be non-blocking with timeout. None-blocking mode with timeout requires the configuration option CYGOPT_IO_CAN_SUPPORT_NONBLOCKING and CYGOPT_IO_CAN_SUPPORT_TIMEOUTS to be enabled, requires the eCos kernel package to be included and the specific device to be set to non-blocking mode for reads (see cyg_io_set_config()). In non-blocking mode with timeouts, if there is no CAN event in receive buffer, the driver waits a certain amount of time (the timeout time) for a CAN event to arrive. If there is still no CAN event in buffer after expiration of the timeout time, -EINTR is returned and the caller must try again.

If an event was successfully received, the function returns ENOERR.

CAN Events

The CAN driver uses cyg_can_event structures to pass events from hardware device driver to the generic CAN driver. A cyg_can_event provides a generic device independent type for handling CAN events that may occur.

typedef struct cyg_can_event_st
{
    cyg_uint32      timestamp;
    cyg_can_event_flags_t flags;
    cyg_can_message msg;
} cyg_can_event;

The structure contains the following fields:

The following events are supported and after receiving an event the application should check the flags field against these values:

CYGNUM_CAN_EVENT_RX               0x00000001 // message received
CYGNUM_CAN_EVENT_TX               0x00000002 // mesage transmitted
CYGNUM_CAN_EVENT_WARNING_RX       0x00000004 // tx error counter (TEC) reached warning level (>96)
CYGNUM_CAN_EVENT_WARNING_TX       0x00000008 // rx error counter (REC) reached warning level (>96)
CYGNUM_CAN_EVENT_ERR_PASSIVE      0x00000010 // CAN "error passive" occured
CYGNUM_CAN_EVENT_BUS_OFF          0x00000020 // CAN "bus off" error occured
CYGNUM_CAN_EVENT_OVERRUN_RX       0x00000040 // overrun in RX queue occured
CYGNUM_CAN_EVENT_OVERRUN_TX       0x00000080 // overrun in TX queue occured
CYGNUM_CAN_EVENT_CAN_ERR          0x00000100 // a CAN bit or frame error occured
CYGNUM_CAN_EVENT_LEAVING_STANDBY  0x00000200 // CAN hardware leaves standby / power down mode or is waked up
CYGNUM_CAN_EVENT_ENTERING_STANDBY 0x00000400 // CAN hardware enters standby / power down mode
CYGNUM_CAN_EVENT_ARBITRATION_LOST 0x00000800 // arbitration lost
CYGNUM_CAN_EVENT_FILTER_ERR       0x00001000 // CAN message filter / acceptance filter error
CYGNUM_CAN_EVENT_PHY_FAULT        0x00002000 // General failure of physical layer detected
CYGNUM_CAN_EVENT_PHY_H            0x00004000 // Fault on CAN-H detected (Low Speed CAN)
CYGNUM_CAN_EVENT_PHY_L            0x00008000 // Fault on CAN-L detected (Low Speed CAN)
CYGNUM_CAN_EVENT_ERR_ACTIVE       0x00010000 // CAN controller now "error active"
CYGNUM_CAN_EVENT_OVERRUN_RX_HW    0x00020000 // CAN controller reports a RX overrun

Often the flags field will contain only one single set flag. But it is possible that a number of flags is set and so the flag field should always be checked by a receiver. Most of the flags are independent from each other and the receiver has to handle each of them separately.

The internal receive buffers of the CAN device driver are circular buffers. That means that even if the buffers are completely filled new messages will be received. In this case the newest message will always overwrite the oldest message in the receive buffer. If this happens the CYGNUM_CAN_EVENT_OVERRUN_RX flag will be set for this new message that caused overwriting of the old one. However if an overrun occurs in the hardware message buffers of the CAN controller, the flag CYGNUM_CAN_EVENT_OVERRUN_RX_HW is raised instead.

Example code for receiving one single CAN event:

cyg_can_event rx_event;
cyg_uint32    len;
Cyg_ErrNo     ret;

len = sizeof(rx_event);
ret = cyg_io_read(hDrvCAN, &rx_event, &len);

if (ENOERR == ret)
{
    if (rx_event.flags & CYGNUM_CAN_EVENT_RX)
    {
        // handle RX event
    }
    
    if (rx_event.flags & ~CYGNUM_CAN_EVENT_RX)
    {
        // handle other events
    }
}
else if (-EINTR == ret)
{
    // handle timeout
}

cyg_io_get_config

cyg_io_get_config(handle, key, buf, len)

This function is used to obtain run-time configuration about a device. The type of information retrieved is specified by the key. The data will be returned in the given buffer. The value of *len should contain the amount of data requested, which must be at least as large as the size appropriate to the selected key. The actual size of data retrieved is placed in *len. The appropriate key values are all listed in the file <cyg/io/config_keys.h>.

The following config keys are currently supported:

CYG_IO_GET_CONFIG_READ_BLOCKING
CYG_IO_GET_CONFIG_WRITE_BLOCKING
CYG_IO_GET_CONFIG_CAN_INFO
CYG_IO_GET_CONFIG_CAN_BUFFER_INFO
CYG_IO_GET_CONFIG_CAN_MSGBUF_INFO
CYG_IO_GET_CONFIG_CAN_TIMEOUT
CYG_IO_GET_CONFIG_CAN_HDI
CYG_IO_GET_CONFIG_CAN_STATE
CYG_IO_GET_CONFIG_CAN_ERR_COUNTERS

cyg_io_set_config

cyg_io_set_config(handle, key, buf, len)

This function is used to manipulate or change the run-time configuration of a device. The type of information is specified by the key. The data will be obtained from the given buffer. The value of *len should contain the amount of data provided, which must match the size appropriate to the selected key. The appropriate key values are all listed in the file <cyg/io/config_keys.h>.

The following config keys are currently supported:

CYG_IO_SET_CONFIG_READ_BLOCKING
CYG_IO_SET_CONFIG_WRITE_BLOCKING
CYG_IO_SET_CONFIG_CAN_INFO
CYG_IO_SET_CONFIG_CAN_OUTPUT_DRAIN
CYG_IO_SET_CONFIG_CAN_OUTPUT_FLUSH
CYG_IO_SET_CONFIG_CAN_INPUT_FLUSH
CYG_IO_SET_CONFIG_CAN_TIMEOUT
CYG_IO_SET_CONFIG_CAN_MSGBUF
CYG_IO_SET_CONFIG_CAN_MODE
CYG_IO_SET_CONFIG_CAN_ABORT
CYG_IO_SET_CONFIG_CAN_CALLBACK
CYG_IO_SET_CONFIG_CAN_RANGE_FILTER
CYG_IO_SET_CONFIG_CAN_MASK_FILTER