CAN Library for Teensy 4.0 / 4.1
It handles Controller Area Network (CAN) for CAN1, CAN2 and CAN3, and Controller Area Network with Flexible Data (CANFD) for CAN3.
Compatibility with the ACAN2515 and ACAN2517 libraries
This library is fully compatible with the MCP2515 CAN Controller ACAN2515 library https://github.com/pierremolinaro/acan2515 and the MCP2517FD, MCP2518FD CAN Controllers ACAN2517 library https://github.com/pierremolinaro/acan2517, it uses a very similar API and the same CANMessage class for handling messages.
Compatibility with the ACAN2517FD library
This library is fully compatible with the MCP2517FD, MCP2518FD CAN Controllers ACAN2517FD library https://github.com/pierremolinaro/acan2517FD, it uses a very similar API and the same CANFDMessage class for handling messages.
ACAN library description
ACAN is a driver for the three FlexCAN modules of the Teensy 4.0 / 4.1 microcontroller. It supports alternate pins for CAN1.
The driver supports many bit rates, as standard 62.5 kbit/s, 125 kbit/s, 250 kbit/s, 500 kbit/s, and 1 Mbit/s. An efficient CAN bit timing calculator finds settings for them, but also for exotic bit rates as 833 kbit/s. If the wished bit rate cannot be achieved, the begin method does not configure the hardware and returns an error code.
Driver API is fully described by the PDF file in the
ACAN_T4/extrasdirectory.
Demo Sketches
The demo sketches are in the
ACAN_T4/examplesdirectory.
The LoopBackDemoCAN1 demo sketch shows how configure the CAN1module, and how to send and revceive frames.
Configuration is a four-step operation.
- Instanciation of the
settingsobject : the constructor has one parameter: the wished CAN bit rate. Thesettingsis fully initialized. - You can override default settings. Here, we set the
mLoopBackModeandmSelfReceptionModeproperties to true, enabling to run demo code without any additional hardware (no CAN transceiver needed). We can also for example change the receive buffer size by setting themReceiveBufferSizeproperty. - Calling the
beginmethod configures the driver and starts CAN bus participation. Any message can be sent, any frame on the bus is received. No default filter to provide. - You check the
errorCodevalue to detect configuration error(s).
void setup () {
pinMode (LED_BUILTIN, OUTPUT) ;
Serial.begin (9600) ;
while (!Serial) {
delay (50) ;
digitalWrite (LED_BUILTIN, !digitalRead (LED_BUILTIN)) ;
}
Serial.println ("CAN1 loopback test") ;
ACAN_T4_Settings settings (125 * 1000) ; // 125 kbit/s
settings.mLoopBackMode = true ;
settings.mSelfReceptionMode = true ;
const uint32_t errorCode = ACAN_T4::can1.begin (settings) ;
if (0 == errorCode) {
Serial.println ("can1 ok") ;
}else{
Serial.print ("Error can1: 0x") ;
Serial.println (errorCode, HEX) ;
}
}
Now, an example of the loop function. As we have selected loop back mode, every sent frame is received.
static uint32_t gBlinkDate = 0 ;
static uint32_t gSendDate = 0 ;
static uint32_t gSentCount = 0 ;
static uint32_t gReceivedCount = 0 ;
void loop () {
if (gBlinkDate <= millis ()) {
gBlinkDate += 500 ;
digitalWrite (LED_BUILTIN, !digitalRead (LED_BUILTIN)) ;
}
CANMessage message ;
if (gSendDate <= millis ()) {
message.id = 0x542 ;
const bool ok = ACAN_T4::can1.tryToSend (message) ;
if (ok) {
gSendDate += 2000 ;
gSentCount += 1 ;
Serial.print ("Sent: ") ;
Serial.println (gSentCount) ;
}
}
if (ACAN_T4::can1.receive (message)) {
gReceivedCount += 1 ;
Serial.print ("Received: ") ;
Serial.println (gReceivedCount) ;
}
}
CANMessage is the class that defines a CAN message. The message object is fully initialized by the default constructor. Here, we set the id to 0x542 for sending a standard data frame, without data, with this identifier.
The ACAN_T4::can1.tryToSend tries to send the message. It returns true if the message has been sucessfully added to the driver transmit buffer.
The gSendDate variable handles sending a CAN message every 2000 ms.
ACAN_T4::can1.receive returns true if a message has been received, and assigned to the messageargument.
Use of Optional Reception Filtering
The hardware defines two kinds of filters: primary and secondary filters. You can define up to 32 primary filters and 96 secondary filters.
This an setup example:
ACANSettings settings (125 * 1000) ;
...
const ACANPrimaryFilter primaryFilters [] = {
ACANPrimaryFilter (kData, kExtended, 0x123456, handle_myMessage_0)
} ;
const ACANSecondaryFilter secondaryFilters [] = {
ACANSecondaryFilter (kData, kStandard, 0x234, handle_myMessage_1),
ACANSecondaryFilter (kRemote, kStandard, 0x542, handle_myMessage_2)
} ;
const uint32_t errorCode = ACAN_T4::can1.begin (settings,
primaryFilters,
1, // Primary filter array size
secondaryFilters,
2) ; // Secondary filter array size
For example, the first filter catches extended data frames, with an identifier equal to 0x123456. When a such frame is received, the handle_myMessage_0 function is called. In order to achieve this by-filter dispatching, you should call ACAN_T4::can1.dispatchReceivedMessage instead of ACAN_T4::can1.receive in the loopfunction:
void loop () {
ACAN_T4::can1.dispatchReceivedMessage () ; // Do not use ACAN_T4::can1.receive any more
...
}
