<tt>can_dm</tt> utilities

Header: **components/drivers/can/can_dm.h** (also installable as drivers/can_dm.h via include path). Implementation: **components/drivers/can/can_dm.c** — only ISO 11898 DLC/length conversion; no device register, OFW, or ISR code.

The CAN device framework is **dev_can.c** — see CAN device.

APIs

rt_uint8_t can_dlc2len(rt_uint8_t can_dlc);

rt_uint8_t can_len2dlc(rt_uint8_t len);

<tt>can_dlc2len</tt>

Maps CAN FD DLC nibble (0–15) to payload byte length:

DLC	0–8	9–12	13–16	17–20	21–24	25–32	33–48	49–64
Bytes	0–8	12	16	20	24	32	48	64

Only low 4 bits of can_dlc are used (can_dlc & 0x0F).

<tt>can_len2dlc</tt>

Inverse mapping for lengths 0–64; returns **0xf** if **len > 64**.

Usage in controllers

FD-capable drivers should:

Store/transmit hardware DLC using **can_len2dlc(actual_payload_len)**.
On RX, convert to byte count with **can_dlc2len(rx_frame.dlc)** before copying to upper layers.

Classic CAN (≤ 8 bytes) uses DLC 0–8 with identity mapping in both tables.

CAN ID flags (header only)

can_dm.h also defines Linux-style ID flags for drivers that pack ID + type into one word:

Macro	Value	Meaning
`CAN_EFF_FLAG`	`0x80000000`	Extended frame
`CAN_RTR_FLAG`	`0x40000000`	Remote frame
`CAN_ERR_FLAG`	`0x20000000`	Error frame
`CAN_SFF_MASK` / `CAN_EFF_MASK`	—	ID field masks

These are not used by dev_can.c (rt_can_msg uses separate ide/rtr bits).

Driver / BSP quick notes

Topic	Guidance
Not a DM bus	No `RT_CAN_OFW_DECLARE` in core — platform drivers (e.g. Rockchip `canfd-rockchip.c`) own OFW probe
FD vs classic	Do not use DLC > 8 on classic-only controllers
Include	`#include "can_dm.h"` or path from driver directory
`can_get_dlc` / `canfd_get_dlc`	Clamp DLC before `can_dlc2len`