The SJA 1000 CAN Controller and Linux Driver

The SJA 1000 CAN Controller and Linux Driver Cristiano Brudna Universität Ulm Fakultät für Informatik Abteilung Rechnerstrukturen 1

Contents " The SJA 1000 �Physical connection, registers, message formats, filtering. " SJA 1000 Linux Driver �How to send and receive messages, special functions. 2

SJA 1000 Basic Features " Pin and electrical compatibility to the PCA 82 C 200 " Extended (29 bit) and Standard (11 bit) Frame Formats " Bit rate up to 1 Mbit/s " Buffer: �Receive buffer: 64 -byte ringbuffer �Transmit buffer: 1 message 3

Physical Connection Microcontroller SJA 1000 TX RX Transceiver (PCA 82 C 250) CAN_H 4 CAN_L CAN bus

Modes of Operation " Basic. CAN (compatible with PCA 82 C 200) �Only Standard Frame Format (11 bit identifiers) �Extended Frame Format is tolerated " Peli. CAN �Standard and Extended Frame Format (11 and 29 bit identifiers) 5

Registers (Peli. CAN mode) " 8 bit registers " Registers for configuration and control �Mode, Command, Interrupt Enable, Bus Timing 0/1, Output Control, Acceptance Code, Acceptance Mask " Registers that provide status �Status, Interrupt, RX Error Counter, TX Error Counter, Error Warning Limit, Error Code Capture, Arbitration Lost capture, RX Message Counter, RX Buffer Start Address, Clock Divider 6

Mode Register " Sleep mode �Goal: save energy �First message will be lost! " Acceptance Filter Mode " Self Test Mode " Listen Only Mode �No ancknowledge is sent, error counters stop " Reset Mode 7

Interrupts " Interrupts provided: �Bus Error �Arbitration Lost �Error Passive �Wake-up �Data Overrun �Error Warning �Transmit �Receive " Can be idividually enabled/disabled 8

Bus Timing 0/1 Registers " Can be written only in RESET MODE " Bus Timing 0 �BTR 0. 7 to 6: Synchronization Jump Width (2 bits) �BTR 0. 5 to 0: Baud Rate Prescaler (6 bits), define TQ " Bus Timing 1 �BTR 1. 7: Sampling (1 bit), 1 or 3 times �BTR 1. 6 to 4: Time Segment 1 (4 bits) �BTR 1. 3 to 0: Time Segment 2 (3 bits) 9

Bus Timing 0/1 Registers (cont) Time quantum (TQ) is used to define segments Nominal bit time SYNC SEG TSEG 1 = 1 TQ Sample point(s) 10 TSEG 2

Error registers " RX error counter: number of receive errors " TX error counter: number of transmit errors " Error code capture: identify the type of error occurred during transmition/reception 11

Data Frame, Remote Frame " Frame Information (1 byte): �FF: frame format �RTR: remote transmission request �DLC: data length code " Identifier: �Standard frame format: 2 bytes �Extended frame format: 4 bytes " Data Bytes: 0 -8 bytes 12

Message Format 13 Standard Frame Extended Frame Tx frame information Tx identifier 1 Tx identifier 2 Tx data byte 1 Tx identifier 3 Tx data byte 2 Tx identifier 4 Tx data byte 3 Tx data byte 1 Tx data byte 4 Tx data byte 2 Tx data byte 5 Tx data byte 3 Tx data byte 6 Tx data byte 4 Tx data byte 7 Tx data byte 5 Tx data byte 8 Tx data byte 6 Tx data byte 7 Tx data byte 8

Filtering " Two modes of filtering: �Single filter: 32 -bit filter " Standard Frame: identifier + RTR + data 1 + data 2 " Extended Frame: identifier + RTR �Dual filter: at least one filter must match " SF: filter 1(ID + RTR + data 1), filter 2 (ID + RTR) " EF: filter 1 and 2 (2 upper bytes of the ID) 14 " Acceptance Mask Register: define relevant bits ('1' = don't care) " Acceptance Code Register: define bits to be matched

Single Filter for Extended Frame Format 15 Byte 0 Byte 1 Byte 2 Message ID ID. 28 to 21 ID. 20 to 13 ID. 12 to 5 Acceptance Mask Register AMR 0 AMR 1 AMR 2 Acceptance Code Register ACR 0 ACR 1 ACR 2 Byte 3 ID. 4 ID. 3 ID. 2 ID. 1 ID. 0 RTR

Single Filter Example Byte 3 Byte 2 Byte 1 Message ID ID. 28 to 21 ID. 20 to 13 ID. 12 to 5 Acceptance Mask Register "1" "1" Acceptance Code Register "0" "0" Byte 0 Accepted 16

Using the SJA 1000 Linux driver " The driver uses receive and transmit interrupts and read and write buffers " File operations for applications: open(), close(), read(), write(), ioctl(), and select(). 17

Using the SJA 1000 Linux driver File operations (1) " Open: provide blocking and non-blocking modes can = open("/dev/can", O_RDWR); can = open("/dev/can", O_RDWR | O_NONBLOCK); " Close: close(can); 18

Using the SJA 1000 Linux driver CAN message data structure typedef struct { Can. Id id; // identifier (11 or 29 bits) int type; // standard (0) or extended frame (1) int rtr; // remote transmission request (1 when true) int len; // data length 0. . 8 unsigned char d[8]; // data bytes struct timeval timestamp; // timestamp for received messages in the format of [seconds, microseconds] since Epoch (january 1. 1970). } canmsg; 19

Using the SJA 1000 Linux driver File operations (2) " Read: return a message from the read buffer �Return '32' when a message is available and -EAGAIN when there is no message. ret = read(can, &msg, sizeof(canmsg)); " Write: write a message to the driver. �Return '32' when the message is succesfully stored in the transmit buffer and -EAGAIN when the buffer is full. 20 ret = write(can, &msg, sizeof(canmsg));

Using the SJA 1000 Linux driver File operations (3) " ioctl: specific control operations. unsigned long baud_rate = B 1000; ioctl(can, CAN_IOCSBAUD, &baud_rate); " Supported operations: �CAN_IOCSBAUD: set baud rate. The following constants are used to set it: B 1000 (1 Mbit/s), B 500 (500 kbit/s), B 250 (250 kbit/s), B 125 (125 kbit/s), B 20 (20 kbit/s). 21

Using the SJA 1000 Linux driver File operations (4) " Supported operations: �CAN_IOCSAMASK: set a 32 -bit acceptance mask. �CAN_IOCSACODE: set a 32 -bit acceptance code. �CAN_IOCCRBUF: clear read buffer. �CAN_IOCCWBUF: clear write buffer. �CAN_IOCRTTS: read the timestamp of the last transmitted message. The timestamp is returned in a timeval data structure. 22

Using the SJA 1000 Linux driver File operations (5) �CAN_IOCSACTIVE: set active mode. �CAN_IOCSPASSIVE: set passive mode. �CAN_IOCRREG: read a SJA 1000 register. The most useful ones for applications are 'ERROR_CODE_CAPTURE' 'RX_ERROR_COUNTER' 'TX_ERROR_COUNTER' 23