On 08.05.2023 08:54:18, Thomas.Kopp@xxxxxxxxxxxxx wrote: > I was working on the same thing on Friday but didn't get around to > sending it off, so here are a couple thoughts I had when working on > the defines in length.h > > The definitions for IFS in here are called intermission in the > standard ACK, and IMF seems to be a common abbreviation. > and I'd argue they shouldn't be part of the frame at all. The diagram in https://www.can-cia.org/can-knowledge/can/can-fd/ suggests that IMF is part of the frame. > To > quote the ISO: "DFs and RFs shall be separated from preceding frames, > whatever frame type they are (DF, RF, EF, OF), by a time period called > inter-frame space." > > So, my suggestion would be to pull out the 3 bit IFS definition that's > currently in and introduce 11 bit Bus idle and if necessary 3 bit > Intermission separately. > > index 6995092b774ec..62e92c1553376 100644 > --- a/include/linux/can/length.h > +++ b/include/linux/can/length.h > @@ -6,6 +6,26 @@ > #ifndef _CAN_LENGTH_H > #define _CAN_LENGTH_H > > +/* > + * First part of the Inter Frame Space > + */ > +#define CAN_INTERMISSION_BITS 3 > + > +/* > + * Number of consecutive recessive bits on the bus for integration etc. > + */ > +#define CAN_IDLE_CONDITION_BITS 11 > + > > The field currently called Stuff bit count (SBC) is also not correct > I'd say. I'm not sure about the history but given that this is > dependent on the DLC I think what's meant is the number of Fixed Stuff > bits (FSB) . The ISO does not define a term for the Stuff bit Count > but the CiA did define/document it this way. What's meant though is > not the number of fixed stuff bits (FSB) which the comment implies > here but the modulo 8 3 bit gray-code followed by the parity bit. So > for the FD frame definitions I'd propose something like this: Renaming > the current SBC to FSB and adding the SBC. > /* > * Size of a CAN-FD Standard Frame > @@ -69,17 +87,17 @@ > * Error Status Indicator (ESI) 1 > * Data length code (DLC) 4 > * Data field 0...512 > - * Stuff Bit Count (SBC) 0...16: 4 20...64:5 > + * Stuff Bit Count (SBC) 4 ACK > * CRC 0...16: 17 20...64:21 > * CRC delimiter (CD) 1 > + * Fixed Stuff bits (FSB) 0...16: 6 20...64:7 As far as I understand https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8338047 the FSB is 5 or 6. > * ACK slot (AS) 1 > * ACK delimiter (AD) 1 > * End-of-frame (EOF) 7 > - * Inter frame spacing 3 > * > - * assuming CRC21, rounded up and ignoring bitstuffing > + * assuming CRC21, rounded up and ignoring dynamic bitstuffing > */ > > Best Regards, > Thomas > Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
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