Interfacing a MCP2515 CAN controller to a Xenon

BMan · July 17, 2019, 11:44pm

Hello, I am new to particle and just started exploring the xenon hardware. I would like to connect a MCP2515 or 2517 to the SPI bus on a xenon board. I have imported the arduino-CAN library and was looking to find where or how I allocate the SPI bus up for the MCP2515. I see the how to set the SPI hardware up for the xenon, but how do I associate it to the arduino-CAN library so using the API to transmit and receive CAN messages uses the SPI hardware? Any help on how that is done is appreciated.

Thank you,

ScruffR · July 18, 2019, 10:52am

Not sure what you mean by that. The HW SPI bus pins on the Xenon are marked MI, MO & SCK and the chip/slave selecte pin is free to choose.
A secondary SPI interface exists on the Xenons too - that can be found here
https://docs.particle.io/reference/device-os/firmware/xenon/#spi

That would typically be the job of the library - it should provide you with high level functions to do exactly that.

When you are referencing a library it's always good to also provide a link to save others the need to search.

BMan · July 18, 2019, 1:11pm

ScruffR,

Apologies, for being unclear. The name of the library is arduino-CAN that I imported. This is the data from the library properties file:

( name=arduino-CAN version=0.0.1
sentence=CAN bus for Particle using the MCP2515
paragraph=This library is intended for the mesh boards which have no onboard CAN controller
url=https://github.com/nzottmann/arduino-CAN
repository=https://github.com/nzottmann/arduino-CAN.git
architectures=*)

I understand the pinning of the Xenon ports and setting them to be used as SPI. I guess what I am asking is how does a library that is imported associate its’ high level interface to the low level SPI pins? Is there usually a place in an imported library to set/define what SPI port pins are being used?

Best Regards,

ScruffR · July 18, 2019, 5:02pm

Via this command

github.com

nzottmann/arduino-CAN/blob/master/src/MCP2515.cpp#L79


      
          {
          }
          
          int MCP2515Class::begin(long baudRate)
          {
            CANControllerClass::begin(baudRate);
          
            pinMode(_csPin, OUTPUT);
          
            // start SPI
            SPI.begin();
          
            reset();
          
            writeRegister(REG_CANCTRL, 0x80);
            if (readRegister(REG_CANCTRL) != 0x80) {
              return 0;
            }
          
            const struct {
              long clockFrequency;

Since that library explicitly uses SPI the pins that are tied to that interface are used.
Only the CS pin could be chosen via this

github.com

nzottmann/arduino-CAN/blob/master/src/MCP2515.h#L49


      
            using CANControllerClass::filter;
            virtual int filter(int id, int mask);
            using CANControllerClass::filterExtended;
            virtual int filterExtended(long id, long mask);
          
            virtual int observe();
            virtual int loopback();
            virtual int sleep();
            virtual int wakeup();
          
            void setPins(int cs = MCP2515_DEFAULT_CS_PIN, int irq = MCP2515_DEFAULT_INT_PIN);
            void setSPIFrequency(uint32_t frequency);
            void setClockFrequency(long clockFrequency);
          
            void dumpRegisters(Stream& out);
          
          private:
            void reset();
          
            void handleInterrupt();

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Interfacing a MCP2515 CAN controller to a Xenon

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