xl2515.c File Reference

The XL2515 over SPI: the part of the CAN driver that touches hardware. More...

#include "xl2515.h"
#include <string.h>
#include "hardware/gpio.h"
#include "hardware/spi.h"
#include "pico/stdlib.h"
#include "can_timing.h"
#include "iomcu_pins.h"
#include "mcp2515.h"

Functions
static void	cs_low (void)
	Drives the chip select low, selecting the part.
static void	cs_high (void)
	Drives the chip select high, deselecting the part.
static void	write_regs (uint8_t addr, const uint8_t *data, size_t n)
	Writes n registers starting at addr, with a WRITE command.
static void	write_reg (uint8_t addr, uint8_t value)
	Writes one register.
static void	read_regs (uint8_t addr, uint8_t *out, size_t n)
	Reads n registers starting at addr, with a READ command.
static uint8_t	read_reg (uint8_t addr)
	Reads one register.
static void	bit_modify (uint8_t addr, uint8_t mask, uint8_t value)
	Read-modify-write in the part rather than here: the interrupt flags are set by the controller between a read and a write, and clearing them with a whole-register write would drop whatever arrived in between.
bool	xl2515_init (uint32_t bitrate)
	Reset, set the bit timing for bitrate, and enter normal mode.
bool	xl2515_send (const link_can_frame_t *f)
	Queue one frame in TXB0 and request transmission.
static bool	fetch_rx (void *ctx, uint8_t buf[13])
	Consume the next full receive buffer, RXB0 before RXB1.
bool	xl2515_recv (link_can_frame_t *f, uint32_t *refused)
	Take one frame from whichever receive buffer has one.
bool	xl2515_take_overflow (void)
	True if a frame arrived with both receive buffers full since the last call.
void	xl2515_errors (uint8_t *tx_errors, uint8_t *rx_errors, uint8_t *flags)
	The controller's own error counters, for the bring-up report.

Detailed Description

The XL2515 over SPI: the part of the CAN driver that touches hardware.

SPDX-License-Identifier: MIT

Function Documentation

bit_modify()

void bit_modify ( uint8_t addr, uint8_t mask, uint8_t value )

static

Read-modify-write in the part rather than here: the interrupt flags are set by the controller between a read and a write, and clearing them with a whole-register write would drop whatever arrived in between.

Parameters

addr	Address of the register.
mask	Bits to change.
value	New value of the bits in mask.

fetch_rx()

bool fetch_rx ( void * ctx, uint8_t buf[13] )

static

Consume the next full receive buffer, RXB0 before RXB1.

Parameters

ctx	Unused.
buf	Receives the 13 bytes of the buffer.

Returns

True when a buffer was read. False when neither holds a frame.

read_reg()

uint8_t read_reg ( uint8_t addr )

static

Reads one register.

Parameters

addr	Address of the register.

Returns

The register value.

read_regs()

void read_regs ( uint8_t addr, uint8_t * out, size_t n )

static

Reads n registers starting at addr, with a READ command.

Parameters

addr	Address of the first register.
out	Receives the n values.
n	Number of registers to read.

write_reg()

void write_reg ( uint8_t addr, uint8_t value )

static

Writes one register.

Parameters

addr	Address of the register.
value	Value to write.

write_regs()

void write_regs ( uint8_t addr, const uint8_t * data, size_t n )

static

Writes n registers starting at addr, with a WRITE command.

Parameters

addr	Address of the first register.
data	Values to write.
n	Number of registers to write.

xl2515_errors()

void xl2515_errors	(	uint8_t *	tx_errors,
		uint8_t *	rx_errors,
		uint8_t *	flags )

The controller's own error counters, for the bring-up report.

Either pointer may be NULL.

Parameters

tx_errors	Receives the transmit error counter (TEC). May be NULL.
rx_errors	Receives the receive error counter (REC). May be NULL.
flags	Receives the error flags register (EFLG). May be NULL.

xl2515_init()

bool xl2515_init

(

uint32_t

bitrate

)

Reset, set the bit timing for bitrate, and enter normal mode.

False if the part does not answer. The datasheet guarantees configuration mode after a reset, so a CANSTAT that says otherwise means nothing is listening on the SPI bus: an SPI wiring fault, not a CAN wiring fault.

Parameters

bitrate

CAN bit rate in bit/s.

Returns

True when the controller is in normal mode. False when the part does not answer, or the crystal cannot make bitrate.

xl2515_recv()

bool xl2515_recv	(	link_can_frame_t *	f,
		uint32_t *	refused )

Take one frame from whichever receive buffer has one.

A buffer holding a frame this link does not carry is consumed, adds 1 to refused (modulo 2^32, NULL counts nothing) and the other buffer is tried. False if none holds a valid frame.

Parameters

f	Receives the frame.
refused	Counts the frames this link does not carry. NULL counts nothing.

Returns

True when a valid frame was taken. False when no buffer holds one.

xl2515_send()

bool xl2515_send

(

const link_can_frame_t *

f

)

Queue one frame in TXB0 and request transmission.

False if the buffer is still busy with the previous one.

Parameters

f	The frame to send. NULL is refused, and so is a DLC above 8.

Returns

True when the frame is queued. False when the buffer is still busy with the previous frame, or the identifier cannot be packed.

xl2515_take_overflow()

bool xl2515_take_overflow

(

void

)

True if a frame arrived with both receive buffers full since the last call.

The flags are sticky and the MCU (microcontroller unit) clears them, which makes this the one record of a frame lost with nothing wrong on the wire: it arrived, it was correct, and there was nowhere to put it. Reading clears them, so the answer covers the time since the last call.

Returns

True when an overflow was seen since the last call.