查看“DFSDM Linux driver”的源代码

==  Article purpose ==
The purpose of this article is to introduce the Linux<sup>&reg;</sup> driver for the [[DFSDM internal peripheral]]:
* Which DFSDM features are supported by the driver
* How to configure, use and debug it
* What is the driver structure, where to the find source code.

== Short Description ==
The DFSDM Linux<sup>&reg;</sup> driver (kernel space) is based on the [[IIO overview|IIO]] and [[ALSA overview|ALSA]] frameworks.
It offers various modes:
# '''IIO direct mode''': single capture on a channel
# '''IIO software buffer''': capture one or more channels
# '''IIO triggered buffer mode''': capture on one or more channels using triggers<br/>It uses hardware triggers available in IIO. See [[TIM Linux driver]] and [[LPTIM Linux driver]].

It offers an extended API<ref name="stm32-dfsdm-adc-h">{{CodeSource | Linux kernel | include/linux/iio/adc/stm32-dfsdm-adc.h}}, DFSDM IIO custom API</ref> for audio usage which allows '''PDM microphones capture''' through a SPI interface.

== Configuration ==
=== Kernel configuration ===
Activate the DFSDM Linux<sup>&reg;</sup> driver in the kernel configuration by using the [[Menuconfig or how to configure kernel|menuconfig]] tool.

==== IIO driver ====
Configuration flag: CONFIG_STM32_DFSDM_ADC
<pre>
Device Drivers  --->
   <*> Industrial I/O support  --->
      Analog to digital converters  --->
         <*> STMicroelectronics STM32 dfsdm adc
         <*>   STMicroelectronics STM32 adc                        # DFSDM ADC IIO driver
</pre>

When using the DFSDM ADC IIO driver (only), the user must also enable the driver for the external analog front-end (e.g. sigma delta modulator).
The generic sigma delta modulators driver may be used for instance (CONFIG_SD_ADC_MODULATOR):
<pre>
Device Drivers  --->
   <*> Industrial I/O support  --->
      Analog to digital converters  --->
         <*> Generic sigma delta modulator                         # sigma delta modulator driver
</pre>

==== Audio driver ====
Configuration flag: CONFIG_SND_SOC_STM32_DFSDM (Note: This configuration depends on [[#IIO_driver|CONFIG_STM32_DFSDM_ADC]])
<pre>
Device Drivers  --->
   <*> Sound card support  --->
      <*>   Advanced Linux Sound Architecture  --->
         <*>   ALSA for SoC audio support  --->
            STMicroelectronics STM32 SOC audio support  --->
               <*> SoC Audio support for STM32 DFSDM               # DFSDM Audio driver for digital microphone capture
</pre>
=== Device tree ===
Refer to the [[DFSDM device tree configuration]] article when configuring the DFSDM Linux kernel driver.

== How to use ==
=== IIO driver ===
In "'''IIO direct mode'''", the conversion result can be read directly from '''sysfs''', see:
[[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 by using '''sysfs''' first. Then, '''character device''' (/dev/iio:deviceX) is used to read data, see [[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]].

For information on the standard IIO consumer interface, please refer to [[IIO_overview#How_to_use_IIO_kernel_API|How to use IIO kernel API]] which gives an example of the IIO consumer kernel API.

=== Audio driver ===
The DFSDM Linux driver can be accessed from userland through an ALSA device. Refer to [[ALSA_overview#How_to_use|ALSA overview]] for information on how to list and use ALSA devices. 

==How to trace and debug==
=== How to monitor ===
The DFSDM driver uses resources such as clocks and GPIOs.
* Refer to [[Pinctrl_overview#How_to_monitor]] to check DFSDM GPIOs.
* Refer to [[Clock_overview#How_to_monitor_with_debugfs]] to check DFSDM clocks.

==== How to monitor with debugfs ====
The DFSDM registers are accessed using REGMAP by ''DFSDM Linux<sup>&reg;</sup> driver''.

It comes with [[Debugfs|debugfs]] entries to dump registers:
 $ {{highlight|cd /sys/kernel/debug/regmap/4400d000.dfsdm/}}
 $ {{highlight|cat registers}}
 000: 00000000
 004: 00000000
 008: 00000000

==== Other ways to monitor ====
* Man can check the DFSDM '''interrupts''' and/or the DFSDM '''DMA''' interrupts:
 $ {{highlight|cat /proc/interrupts}}
            CPU0       CPU1
 ...
  99:          0          0     GIC-0 142 Level     4400d000.dfsdm:filter@0
 100:          0          0     GIC-0 143 Level     4400d000.dfsdm:filter@1
 101:          0          0     GIC-0 144 Level     4400d000.dfsdm:filter@2
 ...

=== How to trace ===
==== IIO driver ====
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.
 {{Board$}} dmesg -n8
 {{Board$}} echo "file drivers/iio/adc/stm32-dfsdm* +p" > /sys/kernel/debug/dynamic_debug/control
To enable dynamic debug at boot time, append the following arguments on the kernel command line:
 loglevel=8 dyndbg="file drivers/iio/adc/stm32-dfsdm* +p"
==== Audio driver ====
Refer to [[ALSA_overview#How_to_trace]] for details on trace tools.

=== How to debug ===
==== Audio driver ====
Refer to [[ALSA_overview#How_to_debug]] for details on debugging tools.

== Source code location ==
It is composed of:
* {{CodeSource | Linux kernel | drivers/iio/adc/stm32-dfsdm-core.c | stm32-dfsdm-core.c}}, core part of DFSDM Linux driver to handle common resources: registers, clock
* {{CodeSource | Linux kernel | drivers/iio/adc/stm32-dfsdm-adc.c | stm32-dfsdm-adc.c}}, ADC part of DFSDM Linux driver to handle '''ADC''' operations
* {{CodeSource | Linux kernel | sound/soc/stm/stm32_adfsdm.c | stm32_adfsdm.c}}, ASoC DAI part of DFSDM Linux driver to handle '''audio''' operations
See also sigma delta modulator driver:
* {{CodeSource | Linux kernel | drivers/iio/adc/sd_adc_modulator.c | sd_adc_modulator.c}}, sigma delta modulator Linux driver to handle analog front-end
==References==
<references />

<noinclude>
[[Category:IIO]]
[[Category:ALSA]]
{{PublicationRequestId | 9772 | 2018-11-28 | AlainF}}
{{ArticleBasedOnModel | Linux driver article model}}
</noinclude>