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CAN

The CAN drivers are really nothing more than a wrapper around the CAN Controller drivers.

When programming you should only interact with these drivers, not directly with the CAN Controller drivers, unless a special case is needed.

CAN drivers should be designed to be robust enough to support different CAN Controllers, if a new CAN Controller in the future does not work properly with these CAN drivers then upgrade them with other CAN Controllers in mind.

 

Functions

The following functions are how you can interact with these CAN drivers:

Syntax Description
void can_accept(filter, filter, filter, mask) Use this to tell the CAN drivers what messages you want to accept.
Only the first filter is mandatory, filters will default to CAN_DEFAULT_FILTER and mask will default to CAN_DEFAULT_MASK.
void can_setup(spi_bus, cs_pin, int_pin) Call this after using can_accept(). It will initailize everything for the CAN drivers that is not already initialized.
can_message* can_receive() Returns a pointer to the next received CAN message. NO_MESSAGE if nothing to receive
void can_transmit() Call this after setting up can_new_msg to transmit the message

These functions are defined and commented in can/interface.h.

 

Variables

The following variables are exposed by the CAN driver for the programmer:

Variable Type Description
can_new_msg can_message Use this to create a new CAN message before calling can_transmit()

 

Constants

The following constants are defined by this library:

Constant Value
CAN_DATA_LENGTH 8
CAN_DEFAULT_MASK 0x000
CAN_DEFAULT_FILTER 0x7FF

 

Predefined Masks and Filters

This library comes with predefined masks and filters to make accepting CAN messages easy.

Constant Value Description
CAN_MASK_ALL_IDS 0x000 Will match any ID, filters don't matter
CAN_MASK_EXACT_IDS 0x7FF Will match exact IDs (e.g., if a filter is 0x403 then this mask will only accept 0x403)
CAN_MASK_BASE_IDS 0x700 This matches the base ID (e.g., if a filter is 0x400 then this mask will accept 0x4xx, but not 0x5xx)
CAN_MASK_SUB_IDS 0x7F0 Matches sub-board IDs (e.g., if a filter is 0x410 then this mask will accept 0x41x, but not 0x40x)