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A small prescaler is beneficial, as this improves the resolution of the
duty_cycle configuration. However if the prescaler is too small, the
maximal possible period becomes considerably smaller than the requested
value.
One situation where this goes wrong is the following: With a parent
clock rate of 208877930 Hz and max_arr = 0xffff = 65535, a request for
period = 941243 ns currently results in PSC = 1. The value for ARR is
then calculated to
ARR = 941243 * 208877930 / (1000000000 * 2) - 1 = 98301
This value is bigger than 65535 however and so doesn't fit into the
respective register field. In this particular case the PWM was
configured for a period of 313733.4806027616 ns (with ARR = 98301 &
0xffff). Even if ARR was configured to its maximal value, only period =
627495.6861167669 ns would be achievable.
Fix the calculation accordingly and adapt the comment to match the new
algorithm.
With the calculation fixed the above case results in PSC = 2 and so an
actual period of 941229.1667195285 ns.
Fixes:
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|---|---|---|
| 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 | ||
| .editorconfig | ||
| .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 reStructuredText 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.