Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitstuffing.
These are all the possible combinations taken into account:
- Classical CAN or CAN-FD
- Standard or Extended frame format
- CAN-FD CRC17 or CRC21
- Include or not intermission
Instead of doing several individual macro definitions, declare the
can_frame_bits() function-like macro. To this extent, do a full
refactoring of the length definitions.
In addition add the can_frame_bytes(). This function-like macro
replaces the existing macro:
- CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
- CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
- CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
- CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
Function-like macros were chosen over inline functions because they
can be used to initialize const struct fields.
The different maximum frame lengths (maximum data length, including
intermission) are as follow:
Frame type bits bytes
-------------------------------------------------------
Classic CAN SFF no bitstuffing 111 14
Classic CAN EFF no bitstuffing 131 17
Classic CAN SFF bitstuffing 135 17
Classic CAN EFF bitstuffing 160 20
CAN-FD SFF no bitstuffing 579 73
CAN-FD EFF no bitstuffing 598 75
CAN-FD SFF bitstuffing 712 89
CAN-FD EFF bitstuffing 736 92
The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
can_frame_bytes(true, true, CANFD_MAX_DLEN).
In addition to the above:
- Use ISO 11898-1:2015 definitions for the names of the CAN frame
fields.
- Include linux/bits.h for use of BITS_PER_BYTE.
- Include linux/math.h for use of mult_frac() and
DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
patch, but the include was previously omitted.
- Add copyright 2023 for myself.
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-4-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].
N.B. The RRS is not to be confused with the Substitute Remote Request
(SRR).
Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF macros.
The total remains unchanged, so this is just a documentation fix.
In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).
[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":
RSS bit [only in FD Frames]
The RRS bit shall be transmitted in FD Frames at the position of
the RTR bit in Classical Frames. The RRS bit shall be transmitted
dominant, but receivers shall accept recessive and dominant RRS
bits.
Fixes: 85d99c3e2a ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-3-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The Stuff Bit Count is always coded on 4 bits [1]. Update the Stuff
Bit Count size accordingly.
In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions called fixed stuff bits [2]. The CRC field starts with
a fixed stuff bit and then has another fixed stuff bit after each
fourth bit [2], which allows us to derive this formula:
FSB count = 1 + round_down(len(CRC field)/4)
The length of the CRC field is [1]:
len(CRC field) = len(Stuff Bit Count) + len(CRC)
= 4 + len(CRC)
with len(CRC) either 17 or 21 bits depending of the payload length.
In conclusion, for CRC17:
FSB count = 1 + round_down((4 + 17)/4)
= 6
and for CRC 21:
FSB count = 1 + round_down((4 + 21)/4)
= 7
Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.
[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":
The CRC field shall contain the CRC sequence followed by a recessive
CRC delimiter. For FD Frames, the CRC field shall also contain the
stuff count.
Stuff count
If FD Frames, the stuff count shall be at the beginning of the CRC
field. It shall consist of the stuff bit count modulo 8 in a 3-bit
gray code followed by a parity bit [...]
[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":
In the CRC field of FD Frames, the stuff bits shall be inserted at
fixed positions; they are called fixed stuff bits. There shall be a
fixed stuff bit before the first bit of the stuff count, even if the
last bits of the preceding field are a sequence of five consecutive
bits of identical value, there shall be only the fixed stuff bit,
there shall not be two consecutive stuff bits. A further fixed stuff
bit shall be inserted after each fourth bit of the CRC field [...]
Fixes: 85d99c3e2a ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This patch adds the function can_skb_get_frame_len() which returns the length
of a CAN frame on the data link layer, including Start-of-frame, Identifier,
various other bits, the actual data, the CRC, the End-of-frame, the Inter frame
spacing.
Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Co-developed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The data field in CAN-FD frames have specifig frame length (0, 1, 2, 3, 4, 5,
6, 7, 8, 12, 16, 20, 24, 32, 48, 64). This function "rounds" up a given length
to the next valid CAN-FD frame length.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-10-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This patch moves all CAN frame length related code of the CAN device
infrastructure into a separate file.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-5-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
