9fde4c557f
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:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.