mcp2515 v0.1.0

MCP2515 CAN controller over SPI.

Application scenarios

• A CAN node on a vehicle or industrial bus.
• A diagnostic bridge between CAN and UART.
• A small sensor network with standard or extended frames.

Contract

typedef struct {
    uint32_t id;
    uint8_t extended;
    uint8_t dlc;
    uint8_t data[8];
} can_frame_t;

uint8_t mcp2515_init(mcp2515_t *device, mcp2515_port_t port,
                     uint8_t clock_mhz, uint16_t bitrate_kbps);
uint8_t mcp2515_send(mcp2515_t *device, const can_frame_t *frame);
uint8_t mcp2515_receive(mcp2515_t *device, can_frame_t *frame);

• clock_mhz is 8, 16, or 20; bitrate_kbps is 125, 250, 500, or 1000.
• send uses TX buffer 0.
• receive polls RX buffer 0/1 and clears the matching interrupt flag.
• Returns 1 on success or a received frame, 0 for no frame or an error.

Parameters

• Bit timing uses the MCP2515 CNF1/CNF2/CNF3 tables for the chosen clock.
• RXB0 accepts all standard and extended frames with rollover enabled.
• A 120 ohm termination is required at each end of the bus.

Memory and timing

• About 8 bytes plus the frame.
• init resets the controller and waits 10 ms.
• A frame write is a 13-byte SPI transfer; no dynamic allocation.

Integration

mcp2515_t can;
can_frame_t frame = {0x123, 0, 2, {0x11, 0x22}};
mcp2515_init(&can, board_mcp2515_port(), 16, 500);
mcp2515_send(&can, &frame);
if (mcp2515_receive(&can, &frame)) {
    handle(frame.id, frame.data, frame.dlc);
}

Adapters

• The adapter drives CS low, transfers SPI bytes, and drives CS high.
• Reference: autowp/arduino-mcp2515 (MIT) and the Microchip MCP2515 datasheet.
• This implementation is original.

When not to use

• A controller with a built-in CAN peripheral; use that instead.
• CAN FD; the MCP2515 supports classical CAN only.

Verification

make test covers the reset and bit timing, a standard frame send, an extended

receive, and the empty-buffer path.

void *context;
void (*select)(void *context);
uint8_t (*transfer)(void *context, uint8_t value);
void (*deselect)(void *context);
void (*delay_ms)(void *context, uint16_t milliseconds);

uint32_t id;
uint8_t extended;
uint8_t dlc;
uint8_t data[8];

mcp2515_port_t port;
uint8_t clock_mhz;
uint16_t bitrate_kbps;