查看“DAC Linux driver”的源代码

== Article purpose ==
This article introduces the Linux<sup>&reg;</sup> driver for the DAC<ref name="DAC internal peripheral">[[DAC internal peripheral]]</ref> internal peripheral:
* Which DAC 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 DAC Linux<sup>&reg;</sup> driver (kernel space) is based on the [[IIO overview|IIO]] framework.

It implements the '''IIO direct mode''', to perform single conversions independently on each channel.<br/>

== Configuration ==
=== Kernel configuration ===
Activate the DAC<ref name="DAC internal peripheral"/> Linux<sup>&reg;</sup> driver in the kernel configuration using the Linux Menuconfig tool: [[Menuconfig or how to configure kernel]] (enable CONFIG_STM32_DAC).
<pre>
Device Drivers  --->
   <*> Industrial I/O support  --->
      Digital to analog converters  --->
         <*> STMicroelectronics STM32 DAC
</pre>

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

== How to use ==
In "IIO direct mode", conversions can be done directly via sysfs. See [[How to use the IIO user space interface#How to do a simple DAC conversion using the sysfs interface|How to do a simple DAC conversion using the sysfs interface]].

== 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 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 DAC registers.

The DAC 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$}} cd /sys/devices/platform/soc/40017000.dac/40017000.dac\:dac@1/
 {{Board$}} 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 DAC 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 dac
        dac12_k                        0        0        0       32000          0 0
                       dac12           1        2        0    98303955          0 0

* '''regulator'''<ref name="Regulator overview">[[Regulator overview]]</ref> tree and usage usage can be verified (e.g. use count, open count and 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 dac
 pin 4 (PA4): device 40017000.dac function {{highlight|analog}} group PA4
 pin 5 (PA5): device 40017000.dac function {{highlight|analog}} group PA5   # check pins are assigned to DAC and configured as "analog"

== Source code location ==
The DAC source code is composed of:
* {{CodeSource | Linux kernel | drivers/iio/dac/stm32-dac-core.c | stm32-dac-core driver}} to handle common resources  such as [[Clock overview|clock]] or [[Regulator overview|regulator]] used as reference voltage and common registers.
* {{CodeSource | Linux kernel | drivers/iio/dac/stm32-dac.c | stm32-dac driver}} to handle the resources available for each DAC such as channel configuration or output buffer handling (power-down mode).

==References==
<references />