Controller Area Network library for NUCLEO boards equipped with CAN peripheral.

Dependents:   Nucleo-Courtois CANBLE CANnucleo_Hello3 Nucleo_Serialprintf ... more

Controller Area Network library for the NUCLEO and DISCOVERY boards equipped with CAN peripheral


Information

Because CAN support has been finally implemented into the mbed library also for the ST boards there is no need to use the CANnucleo library anymore (however you may if you want). The CAN_Hello example is trying to demonstrate the mbed built-in CAN API with NUCLEO boards.


Provides CAN support for the following boards:

with the following features:

device.h

#ifndef MBED_DEVICE_H
#define MBED_DEVICE_H

//=======================================
#define DEVICE_ID_LENGTH       24

#undef DEVICE_CAN

#include "objects.h"

#endif

See the CANnucleo_Hello demo for more details.

Import programCANnucleo_Hello

Using CAN bus with NUCLEO boards (Demo for the CANnucleo library).



Filtering performed by the built-in CAN controller without disturbing the CPU

CANnucleo supports only mask mode and 32-bit filter scale. Identifier list mode filtering and 16-bit filter scale are not supported. There are 14 filters available (0 - 13) for the application to set up. Each filter is a 32-bit filter defined by a filter ID and a filter mask. If no filter is set up then no CAN message is accepted! That's why filter #0 is set up in the constructor to accept all CAN messages by default. On reception of a message it is compared with filter #0. If there is a match, the message is accepted and stored. If there is no match, the incoming identifier is then compared with the next filter. If the received identifier does not match any of the identifiers configured in the filters, the message is discarded by hardware without disturbing the software.

CAN filter function - designed to setup a CAN filter

int CAN::filter(unsigned int id, unsigned int mask, CANFormat format, int handle)

Parameters

id - 'Filter ID' defines the bit values to be compared with the corresponding received bits.

Mapping of 32-bits (4-bytes) :

STID[10:3]STID[2:0] EXID[17:13]EXID[12:5]EXID[4:0] IDE RTR 0

mask - 'Filter mask' defines which bits of the 'Filter ID' are compared with the received bits and which are disregarded.
Mapping of 32-bits (4-bytes) :

STID[10:3]STID[2:0] EXID[17:13]EXID[12:5]EXID[4:0] IDE RTR 0

format - This parameter must be CANAny
handle - Selects the filter. This parameter must be a number between 0 and 13.
retval - 0 - successful, 1 - error, 2 - busy, 3 - time out

Example of filter set up and filtering

Let's assume we would like to accept only messages with standard identifier 0x207:

STID[15:0] = 0x207 = 00000010 00000111


We map the STID to filter ID by shifting the bits adequately:

Filter ID = STID << (16 + (15 - 10)) = STID << 21 = 01000000 11100000 00000000 00000000


To compare only the bits representing STID we set the filter mask appropriately:

Filter mask = 11111111 11100000 00000000 00000100 = 0xFFE00004
              |||||||| |||                    |
              -------- ---                    |
                  |     |                     |
           STID[10:3]  STID[2:0]             IDE


Recall that filter #0 has been set up in the constructor to accept all CAN messages by default. So we have to reconfigure it. If we were set up filter #1 here then filter #0 would accept all the messages and no message would reach filter #1!
To reconfigure (set up) filter #0 we call:

can.filter(0x207 << 21, 0xFFE00004, CANAny, 0);


            Only these bits of 'Filter id' (set to 1 here in 'Filter mask') are compared 
            with the corresponding bits of received message (the others are disregarded)
                                |
                 ---------------------------------
                 |||||||| |||                    |
   Filter mask = 11111111 11100000 00000000 00000100 (= 0xFFE00004)
   Filter id   = 01000000 11100000 00000000 00000000 (= 0x40E00000)
                 |||||||| |||                    |
                 ---------------------------------
                                |
            To accept the message the values of these bits must match.
            Otherwise the message is passed to the next filter or
            discarded if this was the last active filter.
                                |
                 ---------------------------------
                 |||||||| |||                    |
   Received id = 01000000 11100000 00000000 00000010 (= 0x40E00002)
                             ||||| |||||||| ||||| ||
                             -----------------------
                                         |
                          These bits (set to 0 in 'Filter mask') are disregarded (masked).
                          They can have arbitrary values.


NOTE: For the meaning of individual bits see the mapping of 32-bits explained above.

We can use the filter function to setup more (up to 14) CAN filters for example as follows:

can.filter(0x207 << 21, 0xFFE00004, CANAny, 0);    // filter #0
can.filter(0x251 << 21, 0xFFE00004, CANAny, 1);    // filter #1
can.filter(0x304 << 21, 0xFFE00004, CANAny, 2);    // filter #2
...