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int ioctl(int fd, int request, .
..); the CAN controllers control interface - Parameters:
-
| fd | The descriptor to change properties |
| request | special configuration request |
| ... | traditional a char *argp |
The ioctl function manipulates the underlying device parameters of the CAN special device. In particular, many operating characteristics of character CAN driver may be controlled with ioctl requests. The argument fd must be an open file descriptor.
An ioctl request has encoded in it whether the argument is an in parameter or out parameter, and the size of the argument argp in bytes. Macros and defines used in specifying an ioctl request are located in the file can4linux.h .
The following requests are defined:
CAN_IOCTL_COMMAND some commands for start, stop and reset the CAN controller chip CAN_IOCTL_CONFIG configure some of the device properties like acceptance filtering, bit timings, mode of the output control register or the optional software message filter configuration(not implemented yet). CAN_IOCTL_STATUS request the CAN controllers status CAN_IOCTL_SEND a single message over the ioctl interface CAN_IOCTL_RECEIVE poll a receive message CAN_IOCTL_CONFIGURERTR configure automatic rtr responses(not implemented)
The third argument is a parameter structure depending on the request. These are struct Command_par
struct Config_par
struct CanStatusPar
struct ConfigureRTR_par
struct Receive_par
struct Send_par
- Bit Timing
- The bit timing can be set using the ioctl(CONFIG,.. ) and the targets CONF_TIMING or CONF_BTR. CONFIG_TIMING should be used only for the predifined Bit Rates (given in kbit/s). With CONF_BTR it is possible to set the CAN controllers bit timing registers individually by providing the values in val1 (BTR0) and val2 (BTR1).
- Acceptance Filtering
Basic CAN. In the case of using standard identifiers in Basic CAN mode for receiving CAN messages only the low bytes are used to set acceptance code and mask for bits ID.10 ... ID.3
- PeliCAN. For acceptance filtering the entries
AccCode and AccMask are used like specified in the controllers manual for Single Filter Configuration . Both are 4 byte entries. In the case of using standard identifiers for receiving CAN messages also all 4 bytes can be used. In this case two bytes are used for acceptance code and mask for all 11 identifier bits plus additional the first two data bytes. The SJA1000 is working in the Single Filter \ Mode .
Example for extended message format Bits
mask 31 30 ..... 4 3 2 1 0
code
-------------------------------------------
ID 28 27 ..... 1 0 R +--+-> unused
T
R
acccode = (id << 3) + (rtr << 2)
Example for base message format Bits
mask 31 30 ..... 23 22 21 20 ... 0
code
-------------------------------------------
ID 11 10 ..... 1 0 R +--+-> unused
T
R
You have to shift the CAN-ID by 5 bits and two bytes to shift them into ACR0 and ACR1 (acceptance code register) acccode = (id << 21) + (rtr << 20)
- Returns:
- On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- Example
Config_par_t cfg;
volatile Command_par_t cmd;
cmd.cmd = CMD_STOP;
ioctl(can_fd, CAN_IOCTL_COMMAND, &cmd);
cfg.target = CONF_ACCM;
cfg.val = acc_mask;
ioctl(can_fd, CAN_IOCTL_CONFIG, &cfg);
cfg.target = CONF_ACCC;
cfg.val = acc_code;
ioctl(can_fd, CAN_IOCTL_CONFIG, &cfg);
cmd.cmd = CMD_START;
ioctl(can_fd, CAN_IOCTL_COMMAND, &cmd);
- Setting the bit timng register
can4linux provides direct access to the bit timing registers, besides an implicite setting using the ioctl CONF_TIMING and fixed values in Kbit/s. In this case ioctl(can_fd, CAN_IOCTL_CONFIG, &cfg); is used with configuration target CONF_BTR The configuration structure contains two values, val1 and val2 . The following relation to the bit timing registers is used regarding the CAN controller:
val1 val2
SJA1000 BTR0 BTR1
BlackFin CAN_CLOCK CAN_TIMING
FlexCAN (to implement)
- Bit timings are coded in a table in the <hardware>funcs.c file. The values for the bit timing registers are calculated based on a fixed CAN controller clock. This can lead to wrong bit timings if the processor (or CAN) uses another clock as assumed at compile time. Please check carefully. Depending on the clock, it might be possible that not all bit rates can be generated. (e.g. th Blackfin only supports 100, 125, 250, 500 and 1000 Kbit/s (currently!))
- Other CAN_IOCTL_CONFIG configuration targets
(see can4linux.h) CONF_LISTEN_ONLY_MODE if set switch to listen only mode
(default false)
CONF_SELF_RECEPTION if set place sent messages back in the rx queue
(default false)
CONF_BTR configure bit timing directly registers
CONF_TIMESTAMP if set fill time stamp value in message structure
(default true)
CONF_WAKEUP if set wake up waiting processes (default true)
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