查看“Hardware random overview”的源代码

==Article Purpose==
This article gives information about the hardware random (HWRNG) framework.

==Framework purpose==
The Hardware random framework is integrated in the kernel. It provides access to RNG peripherals and focuses on supporting the hardware number generator.

==System overview==
The HW random framework allows retrieving random numbers in userland.

[[File:hwrngapi.png|thumb|center|766px|link=|alt=Alternate text|Hw Random]]

===Component description===
* '''HW random core''' (Kernel space) <br>
Generic interface in kernel space. This layer is in charge of creating the character device (char device) and sysfs to access hw_random.

* '''RNG''' (Kernel space)
Hardware random Linux<sup>&reg;</sup> drivers handling the HW blocks.

* '''RNG''' (Hardware)
HW blocks handling the RNG peripheral.

===API description===
The Hardware random framework uses char device API<ref>https://bootlin.com/doc/legacy/accessing-hardware/accessing-hardware.pdf</ref> ioctl operations.
For additional information, refer to:
* sysfs interface.
* Kernel Documentation directory<ref>{{CodeSource | Linux kernel | Documentation/hw_random.txt}}</ref>

==Configuration==
===Kernel configuration===
The Hardware random support is activated by default in ST deliveries. No specific configuration is required apart from enabling or disabling peripheral support using Linux<sup>&reg;</sup> Menuconfig tool. Refer to [[Menuconfig or how to configure kernel | Menuconfig or how to configure kernel ]] and select:
<pre>
  [*] Device Drivers --->
    [*] Character devices --->
      [*] Hardware Random Number Generator Core support --->
        [*] STMicroelectronics STM32 random number generator
</pre>

===Device tree configuration===
DT configuration can be done thanks to the [[STM32CubeMX]].

A detailed device tree configuration is described in [[RNG device tree configuration]].

== How to use the framework ==
The framework provides external interfaces from userland : [[How_to_control_a_RNG_in_userspace|How to control RNG]].

=== How to use from char device ===
The community tool for using Hardware random framework is rng_tools<ref name=rngtools>[https://git.kernel.org/pub/scm/utils/kernel/rng-tools/rng-tools.git/ Rng_tools source code]</ref> which provides a complete set of utilities related to random number generators:

* '''rngd''': runs a background daemon that opens /dev/hwrng file (default) to connect and retrieve random numbers.
* '''rngtest''': runs different tests that check the entropy and verify the compliance regarding FIPS 140-2 standard.

=== How to use from sysfs ===
Available devices compatible with Hardware framework can be listed using sysfs commands:

  {{Board$}} cat /sys/class/misc/hw_random/rng_available
  '''stm32-rng'''

The selected device is shown here:
  {{Board$}} cat /sys/class/misc/hw_random/rng_current
  '''stm32-rng'''

To select a different device:
  {{Board$}} echo "stm32-rng"> /sys/class/misc/hw_random/rng_current

==How to trace and debug the framework==
Light information on the framework can be accessed by using [[#How_to_use_from_sysfs|sysfs]].

By default, the framework does not provide any specific debug output or dynamic debugging tool.

==Source code location==
Hardware random drivers and framework are available here<ref>{{CodeSource | Linux kernel | drivers/char/hw_random}}, Hw_random sources</ref>.

==To go further==
Code examples are directly available from rng-tools<ref name=rngtools/> github.

==References==

<references />

<noinclude>
{{ArticleBasedOnModel | Framework overview article model}}
{{PublicationRequestId | 9410 | 2018-10-24 | AnneJ}}
[[Category:Security]]
</noinclude>