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can command

Name

can - Tcl interface to Linux SocketCAN

Synopsis

package require Tcl 8.6
package require tclcan
can bcmopen ifname
can bitrate ifname ?rate? ?sample_point?
can bittiming ifname
can bitttiming_const ifname
can berr ifname
can clock ifname
can close chan
can ctrlmode ifname ?mode ...?
can devstat ifname
can dump chan
can interfaces
can open ifname
can read chan
can restart ifname
can restart_ms ifname ?ms?
can start ifname
can state ifname
can stop ifname
can write chan canid data ?ifindex?
can write chan opcode flags count time1 time2 canid ?ifindex ...?

Description

This package provides Tcl support for Linux SocketCAN CAN_RAW and CAN_BCM socket types. The package implements a new channel type and a Tcl command to perform operations on these channels. The standard gets, puts, and read Tcl commands are not supported, but close, fconfigure, and fileevent are available as for normal channels, e.g. sockets. When the libsocketcan shared library is available, various subcommands can be used to manage CAN interfaces, too.

Commands

can bcmopen ifname

Opens a channel by creating a broadcast manager socket (type CAN_BCM ) on the given CAN interface ifname. If ifname is specified as an empty string, the channel is bound to all CAN interfaces. The command returns an identifier for the channel which is to be used in subsequent can read and can write commands.

can bitrate ifname ?rate? ?sample_point?

Gets or sets the bitrate rate (and sets optional sample point to sample_point) on the CAN interface ifname.

can bittiming ifname

Retrieves the current bit timing of the CAN interface ifname. For details refer to /usr/include/can_netlink.h.

can bittiming_const ifname

Retrieves configuration on bit timing of the CAN interface ifname. For details refer to /usr/include/can_netlink.h.

can berr ifname

Retrieves error counters of the CAN interface ifname. The result is a dictionary made up of the keys txerr and rxerr with respective integer error counters.

can clock ifname

Retrieves the clock frequency of the CAN interface ifname. For details refer to /usr/include/can_netlink.h.

can close chan

Closes the channel chan which was formerly obtained by can open. This is equivalent to invoking the close command with chan as parameter.

can ctrlmode ifname ?mode ...?

Gets or sets modes on the CAN interface ifname. If no mode is specified, the current active modes are returned as a list. Otherwise, mode must be one or more words of loopback, listenonly, 3_samples, one_shot, berr_reporting, fd, and presume_ack. In order to turn a mode off, prefix the word with a minus sign. Likewise, to turn it on, a plus sign may be optionally used as prefix.

can devstats ifname

Retrieves device statistics as a dictionary. For details refer to /usr/include/libsocketcan.h and /usr/include/can_netlink.h.

can dump chan

Reads a CAN_RAW or CAN_BCM message off chan and returns a formatted representation of it as a list. The list is empty if no CAN message was pending on chan.

Otherwise, for CAN_RAW channels the list has five or six elements which are: 1. an integer time stamp equivalent to clock microseconds, 2. the interface index (see can interfaces), 3. the CAN identifier as a hexadecimal string with 0x prefix, 4. a frame format tag of the CAN message as EFF (extended frame format) or SFF (standard frame format) optionally followed by |RTR (remote transmission request) or |ERR (error frame), 5. the data length as a decimal number, and optionally 6. the data portion of the CAN message as hexadecimal dump without blanks and prefix.

For CAN_BCM channels the list is made up of: 1. an integer time stamp equivalent to clock microseconds, 2. the interface index (see can interfaces), 3. the major CAN identifier as a hexadecimal string with 0x prefix, 4. a frame format tag as described above, 5. the BCM opcode as one of TX_STATUS, TX_EXPIRED, RX_STATUS, RX_TIMEOUT, or RX_CHANGED, 6. the BCM flags separated by vertical bars (SETTIMER, STARTTIMER, TX_COUNTEVT, TX_ANNOUNCE, TX_CP_CAN_ID, RX_FILTER_ID, RX_CHECK_DLC, RX_NO_AUTOTIMER, TX_RESET_MULTI_IDX, and RX_RTR_FRAME), 7. the BCM count field, 8. the first BCM interval field as floating point number, 9. the second BCM interval field as floating point number, optionally 10. to 13. describing the first CAN frame as CAN identifier (hexadecimal string), the frame format tag (EFF, SFF, etc.), the data length, and the payload as hexadecimal dump. Fields 10. to 13. repeat for the respective number of CAN frames contained in the BCM message.

can interfaces

Returns a list of CAN network interface names and indices suitable for can open, can read, can write and link management subcommands.

can open ifname

Opens a channel (raw AF_CAN socket) on the given CAN interface ifname. If ifname is specified as an empty string, the channel is bound to all CAN interfaces. The command returns an identifier for the channel which is to be used in subsequent can read and can write commands.

can read chan

Reads a CAN_RAW or CAN_BCM message off chan as a list. The list is empty if no CAN message was pending on chan.

Otherwise, for CAN_RAW channels it is made up of four elements, 1. the CAN identifier as an integer number including flags as explained below, 2. the data portion of the CAN message as a byte array, 3. the interface index of the CAN interface the CAN message was received from, and 4. a boolean value indicating if more CAN messages can be read using can read.

For CAN_BCM channels it is made up of at least seven elements: 1. the interface index, 2. the major CAN identifier (see above), 3. the BCM operation as one of TX_STATUS, TX_EXPIRED, RX_STATUS, RX_TIMEOUT, or RX_CHANGED, 4. the BCM flags as an integer number, 5. the BCM count field as an integer number, 6. the first BCM interval field as a floating point number, and 7. the second BCM interval field as a floating point number. When CAN frames are part of the BCM message, each frame is a pair of CAN identifier as integer number and the payload as byte array of length 0 to 8 for normal frames or an integer number for RTR frames.

can restart ifname

Performs a link restart on the CAN interface ifname.

can restart_ms ifname ?ms?

Gets or sets the restart timer of the CAN interface ifname. ms must be specified as positive integer number of milliseconds.

can start ifname

Performs a link startup on the CAN interface ifname.

can state ifname

Retrieves the linmk state of the CAN interface ifname. The result is one of error_active, error_warning, error_passive, bus_off, stopped, sleeping, or unknown.

can stop ifname

Performs a link stop on the CAN interface ifname.

can write chan canid data ?ifindex?

Writes a CAN_RAW message to chan. canid is the CAN identifier as integer number, data a byte array of the data to be sent. The optional ifindex is the CAN interface index (see can interfaces) on which the message is to be sent. It is mandatory to specify ifindex when chan is bound to all interfaces, i.e. the interface name on can open was an empty string.

can write chan opcode flags count time1 time2 canid ?ifindex ...?

Writes a CAN_BCM message to chan. opcode must be a BCM operation out of the set TX_SETUP, TX_DELETE, TX_READ, TX_SEND, RX_SETUP, RX_DELETE, and RX_READ. flags must be a list with zero or more elements of the set SETTIMER, STARTTIMER, TX_COUNTEVT, TX_ANNOUNCE, TX_CP_CAN_ID, RX_FILTER_ID, RX_CHECK_DLC, RX_NO_AUTOTIMER, RX_ANNOUNCE_RESUME, TX_RESET_MULTI_IDX, and RX_RTR_FRAME. count is the counter for the first interval time1. The intervals time1 and time2 must be given as floating point numbers of seconds. canid is the major CAN identifier for the BCM message. ifindex is the interface index which is required, if the CAN_BCM channel was bound to all interfaces. All following optional arguments make up CAN frames and must be pairs of a CAN identifier and a byte array of 0 up to 8 bytes for normal frames, or an integer as data length for RTR frames.

CAN Identifiers

The Linux SocketCAN interface defines special bits in CAN identifiers which are made up of the three most significant bits in a 32 bit integer: 0x80000000 for extended frame format (EFF), 0x40000000 for remote transmission request (RTR), and 0x20000000 for error frames (ERR). The lower 29 (for EFF) or 11 (for SFF) bits make up the CAN identifier. In order to retrieve the real CAN identifier of a received CAN message from can read a binary and with the masks 0x1FFFFFFF or 0x7FF must be carried out. In order to send an RTR message, the CAN identifier must be binary or-ed with 0x40000000 for can write. In order to send a 29 bit CAN identifier it must be or-ed with 0x80000000.

Channel Options

The following list describes the additional channel options of CAN channels.

-error

The last system error message on the channel. This is a read-only option.

-filter ?list?

Message filters applied on reception. list must be made up of an even number of integers specifying CAN identifiers and masks. The default is no filtering, expressed as two zero values. Up to 16 filters can be specified. For details refer to /usr/include/linux/can.h.

-loopback ?bool?

Messages sent are looped back on the local system when enabled (on by default).

-ownmsgs ?bool?

Messages sent are received on the same channel when enabled (off by default).

Link Management

The link management subcommands bitrate, bittiming, bittiming_const, berr, clock, ctlrmode, devstat, restart, restart_ms, start, state, and stop depend on an installed libsocketcan shared library for proper operation. Otherwise they report "function not implemented". All changes of link state by these commands usually require administrative rights. Either the calling process must have super user privileges or the CAP_NET_ADMIN capability must be effective. The latter can be achieved by a command similar to:

    setcap cap_net_admin+eip binary-package-requiring-tclcan

Furthermore, retrieving link information depends on CAN driver support. Usually, the virtual CAN driver vcan and drivers attached through a serial line discipline (using the slcan_attach or slcand programs) only provide rudimentary link state information.

Broadcast Manager Examples

Open BCM channel:

    set chan [can bcmopen can0]

Schedule sending the pattern 0x41424344 on CAN identifier 0x123 once per second:

    can write $chan TX_SETUP \
        {SETTIMER STARTTIMER} \
        0 0.0 1.0 0x123 0x123 ABCD

Dispatch receiving CAN identifier 0x123 with update rate limited to two seconds:

    can write $chan RX_SETUP \
        {SETTIMER RX_FILTER_ID RX_ANNOUNCE_RESUME} \
        0 0.0 2.0 0x123

Dump all received BCM messages on standard output:

    proc dump chan {puts [can dump $chan]}
    fileevent $chan readable [list dump $chan]