查看“ADC Linux driver”的源代码

== Article purpose ==
This article introduces the Linux<sup>&reg;</sup> driver for the ADC<ref name="ADC internal peripheral">[[ADC internal peripheral]]</ref> internal peripheral:
* Which ADC features are supported by the driver
* How to configure, use and debug the driver 
* What is the driver structure, and where the source code can be found.

== Short description ==
The ADC Linux<sup>&reg;</sup> driver (kernel space) is based on the [[IIO overview|IIO]] framework.
It supports two modes:
# '''IIO direct mode''': single capture on a channel (using interrupts)
# '''IIO triggered buffer mode''': capture on one or more channels (preferably using DMA).<br/>It uses the hardware triggers available in IIO. See [[TIM Linux driver]] and [[LPTIM Linux driver]].

== Configuration ==
=== Kernel configuration ===
Activate the ADC<ref name="ADC internal peripheral"/> Linux<sup>&reg;</sup> driver in the kernel configuration using the Linux Menuconfig tool: [[Menuconfig or how to configure kernel]] (enable both CONFIG_STM32_ADC_CORE and CONFIG_STM32_ADC).
<pre>
Device Drivers  --->
   <*> Industrial I/O support  --->
      Analog to digital converters  --->
         <*> STMicroelectronics STM32 adc core
         <*>   STMicroelectronics STM32 adc
</pre>

=== Device tree ===
Refer to the [[ADC device tree configuration]] article when configuring the ADC Linux kernel driver.

== How to use ==
In "'''IIO direct mode'''", the conversion result can be read directly from '''sysfs''' (refer to
[[How to use the IIO user space interface#How to do a simple ADC conversion using the sysfs interface|How to do a simple ADC conversion using the sysfs interface]]).

In "'''IIO triggered buffer mode'''", the configuration must be performed using '''sysfs''' first. Then, '''character device''' (/dev/iio:deviceX) is used to read data (refer to [[How to use the IIO user space interface#Convert one or more channels using triggered buffer mode|Convert one or more channels using triggered buffer mode]]).

== How to trace and debug ==
Refer to [[IIO_overview#How_to_trace_with_dynamic_debug|How to trace with dynamic debug]] for how to '''enable the debug logs''' in the driver and in the framework.

Refer to [[IIO_overview#How_to_debug_with_debugfs|How to debug with debugfs]] for how to '''access the ADC registers'''.

The ADC has system wide dependencies towards other key resources:
* '''runtime power management''' can be disabled, for example it may be forced '''on''' via ''power/control'' sysfs entry:
 {{Board$}} cd /sys/devices/platform/soc/48003000.adc/48003000.adc:adc@0
 {{Board$}} cat power/autosuspend_delay_ms
 2000
 {{Board$}} cat power/control
 auto                                     # kernel is allowed to automatically suspend the ADC device after autosuspend_delay_ms
 {{Board$}} {{highlight|echo on > power/control}}         # force the kernel to resume the ADC device (e.g. keep clocks and regulators enabled)
{{Info| It might be useful to disable runtime power management, in order to dump registers by any means or to check clock and regulator usage (see example below).}}

* '''clock'''<ref name="Clock overview">[[Clock overview]]</ref> usage can be verified by reading ''clk_summary'':
 {{Board$}} {{highlight|cat /sys/kernel/debug/clk/clk_summary}} | grep adc
          adc12_k                     1        1        0    24000000          0 0
                   adc12              1        1        0   196607910          0 0

* '''regulator'''<ref name="Regulator overview">[[Regulator overview]]</ref> tree and usage can be verified (e.g. use count, open count or regulator reference voltage) as follows:
 {{Board$}} {{highlight|cat /sys/kernel/debug/regulator/regulator_summary}}
  regulator                      use open bypass voltage current     min     max
 -------------------------------------------------------------------------------
     v3v3                          4    5      0  3300mV     0mA  3300mV  3300mV
        vdda                       1    2      0  2900mV     0mA  2900mV  2900mV 
           40017000.dac                                              0mV     0mV
           48003000.adc                                              0mV     0mV

* '''pinctrl'''<ref name="Pinctrl_overview">[[Pinctrl overview]]</ref> usage can be verified by reading ''pinmux-pins'':
 {{Board$}} cd /sys/kernel/debug/pinctrl/soc\:pin-controller@50002000/
 {{Board$}} {{highlight|cat pinmux-pins}} | grep adc
 pin 92 (PF12): device 48003000.adc function {{highlight|analog}} group PF12   # check pin is assigned to ADC and is configured as "analog"

* '''interrupts''' can be verified by reading "interrupts":
 {{Board$}} {{highlight|cat /proc/interrupts}}
            CPU0       CPU1
  56:          2          0     dummy   0 Edge      48003000.adc:adc@0

== Source code location ==
The ADC source code is composed of:
* {{CodeSource | Linux kernel | drivers/iio/adc/stm32-adc-core.c | stm32-adc-core driver}} to handle common resources such as clock (selection, prescaler), [[Regulator overview|regulator]] used as reference voltage, interrupt and common registers.
* {{CodeSource | Linux kernel | drivers/iio/adc/stm32-adc.c | stm32-adc driver}} to handle the resources available for each ADC such as  channel configuration and buffer handling.

==References==
<references />

<noinclude>
[[Category:IIO]]
{{PublicationRequestId | 9337 | 2018-10-23 | AnneJ}}
{{ArticleBasedOnModel | Linux driver article model}}
</noinclude>