DAC Linux driver
目录
Article purpose
本文介绍了用于DAC driver for the DAC[1] 内部外围设备的Linux®驱动程序：
- 驱动程序支持哪些DAC功能
- 如何配置，使用和调试驱动程序
- 驱动程序的结构是什么，以及在哪里可以找到源代码
Short Description
DAC Linux® 驱动程序（内核空间）基于 IIO 框架。
它实现了IIO直接模式，以在每个通道上独立执行单个转换。
Configuration
Kernel configuration
Activate the DAC[1] Linux® driver in the kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel (enable CONFIG_STM32_DAC).
Device Drivers --->
<*> Industrial I/O support --->
Digital to analog converters --->
<*> STMicroelectronics STM32 DAC
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 do a simple DAC conversion using the sysfs interface.
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[2] 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[3] 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[4] 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"
Source code location
The DAC source code is composed of:
- drivers/iio/dac/stm32-dac-core.c | |}} stm32-dac-core driver to handle common resources such as clock or regulator used as reference voltage and common registers.
- 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).
