DAC Linux driver
1 Article purpose
This article introduces the Linux® driver for the DAC 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.
2 Short Description
The DAC Linux® driver (kernel space) is based on the IIO framework.
It implements the IIO direct mode, to perform single conversions independently on each channel.
3.1 Kernel configuration
Device Drivers ---> <*> Industrial I/O support ---> Digital to analog converters ---> <*> STMicroelectronics STM32 DAC
3.2 Device tree
Refer to the DAC device tree configuration article when configuring the DAC Linux kernel driver.
4 How to use
In "IIO direct mode", conversions can be done directly via sysfs. See How to do a simple DAC conversion using the sysfs interface.
5 How to trace and debug
Refer to How to trace with dynamic debug for how to enable debug logs in the driver and in the Framework.
Refer to 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 $> echo on > power/control # force the kernel to resume the DAC device (e.g. keep clocks and regulators enabled)
|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 usage can be verified by reading clk_summary:
Board $> 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 tree and usage usage can be verified (e.g. use count, open count and regulator reference voltage) as follows:
Board $> 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 usage can be verified by reading pinmux-pins:
Board $> cd /sys/kernel/debug/pinctrl/soc\:pin-controller@50002000/ Board $> cat pinmux-pins | grep dac pin 4 (PA4): device 40017000.dac function analog group PA4 pin 5 (PA5): device 40017000.dac function analog group PA5 # check pins are assigned to DAC and configured as "analog"
6 Source code location
The DAC source code is composed of:
- stm32-dac-core driver to handle common resources such as clock or regulator used as reference voltage and common registers.
- stm32-dac driver to handle the resources available for each DAC such as channel configuration or output buffer handling (power-down mode).
Industrial I/O Linux subsystem
Analog-to-digital converter. The process of converting a sampled analog signal to a digital code that represents the amplitude of the original signal sample.