On Wed. 31 May 2023 at 00:56, Simon Horman <simon.horman@xxxxxxxxxxxx> wrote: > On Tue, May 30, 2023 at 11:46:37PM +0900, Vincent Mailhol wrote: > > Introduce a method to calculate the exact size in bits of a CAN(-FD) > > frame with or without dynamic bitsuffing. > > > > 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) > > > > 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 name 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. > > > > Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > > ... > > > +/** > > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing > > + * @bitstream_len: length of a destuffed bit stream > > Hi Vincent, > > it looks like an editing error has crept in here: > > s/bitstream_len/destuffed_len/ Doh! Thanks for picking this up. I already prepared a v4 locally. Before sending it, I will wait one day to see if there are other comments. > > + * > > + * The worst bit stuffing case is a sequence in which dominant and > > + * recessive bits alternate every four bits: > > + * > > + * Destuffed: 1 1111 0000 1111 0000 1111 > > + * Stuffed: 1 1111o 0000i 1111o 0000i 1111o > > + * > > + * Nomenclature > > + * > > + * - "0": dominant bit > > + * - "o": dominant stuff bit > > + * - "1": recessive bit > > + * - "i": recessive stuff bit > > + * > > + * Aside of the first bit, one stuff bit is added every four bits. > > + * > > + * Return: length of the stuffed bit stream in the worst case scenario. > > + */ > > +#define can_bitstuffing_len(destuffed_len) \ > > + (destuffed_len + (destuffed_len - 1) / 4)
