[phyBOARD-i.MX 8M Plus Development Board] Evaluation 4: Controlling LED on and off with files in the system root directory

mameng

[phyBOARD-i.MX 8M Plus Development Board] Evaluation 4: Controlling LED on and off with files in the system root directory [Copy link]

 

Detailed interpretation of the official BSP of the development board

https://www.phytec.de/cdocuments/?doc=FwDZGQ

File System:

GPIO control process

GPIOs
The phyBOARD-Polaris has a set of pins especially dedicated as user I/Os. Those pins are connected directly to i.MX 8M pins and are muxed as GPIOs. They are directly usable in Linux userspace. The processor has organized its GPIOs into five banks of 32 GPIOs each (GPIO1 – GPIO5) and one bank with 14 GPIOs. gpiochip0, gpiochip32, gpiochip64, gpiochip96, and gpiochip128 are the sysfs representation of these internal i.MX 8M GPIO banks GPIO1 – GPIO5.

The GPIOs are identified as GPIO<X>_<Y> (e.g. GPIO5_07). <X> identifies the GPIO bank and counts from 1 to 5, while <Y> stands for the GPIO within the bank. <Y> is counted from 0 to 31 (32 GPIOs on each bank).

By contrast, the Linux kernel uses a single integer to enumerate all available GPIOs in the system. The formula to calculate the correct number is:

Linux GPIO number: <N> = (<X> - 1) * 32 + <Y>
Accessing GPIOs from userspace will be done using the libgpiod. It provides a library and tools for interacting with the Linux GPIO character device. Examples of the usage for some of the tools:

Detecting the gpiochips on the chip: 
target$ gpiodetect
gpiochip0 [30200000.gpio] (32 lines)
gpiochip1 [30210000.gpio] (32 lines)
gpiochip2 [30220000.gpio] (32 lines)
gpiochip3 [30230000.gpio] (32 lines)
gpiochip4 [30240000.gpio] (32 lines)
Show detailed information about the gpiochips. Like their names, consumers, direction, active state, and additional flags:
target$ gpioinfo gpiochip0
Read the value of a GPIO (e.g GPIO 20 from chip0):
target$ gpioget gpiochip0 20
Set value of GPIO 20 on chip0 to 0 and exit tool:
target$ gpioset --mode=exit gpiochip0 20=0
Help text of gpioset shows possible options:
target$ gpioset --help
Usage: gpioset [OPTIONS] <chip name/number> <offset1>=<value1> <offset2>=<value2> ...
Set GPIO line values of a GPIO chip
 
Options:
  -h, --help:           display this message and exit
  -v, --version:        display the version and exit
  -l, --active-low:     set the line active state to low
  -m, --mode=[exit|wait|time|signal] (defaults to 'exit'):
                tell the program what to do after setting values
  -s, --sec=SEC:        specify the number of seconds to wait (only valid for --mode=time)
  -u, --usec=USEC:      specify the number of microseconds to wait (only valid for --mode=time)
  -b, --background:     after setting values: detach from the controlling terminal
 
Modes:
  exit:         set values and exit immediately
  wait:         set values and wait for user to press ENTER
  time:         set values and sleep for a specified amount of time
  signal:       set values and wait for SIGINT or SIGTERM
 
Note: the state of a GPIO line controlled over the character device reverts to default
when the last process referencing the file descriptor representing the device file exits.
This means that it's wrong to run gpioset, have it exit and expect the line to continue
being driven high or low. It may happen if given pin is floating but it must be interpreted
as undefined behavior.


Warning

Some of the user IOs are used for special functions. Before using a user IO, refer to the schematic or the hardware manual of your board to ensure that it is not already in use.

Pinmuxing of some GPIO pins in the device tree phytec-imx8mq-phyboard-polaris.dtsi:

                pinctrl__leds: leds1grp {
                        fsl,pins = <
                               MX8MQ_IOMUXC_GPIO1_IO01_GPIO1_IO1   0x16
                               MX8MQ_IOMUXC_I2C3_SCL_GPIO5_IO18    0x16
                               MX8MQ_IOMUXC_SAI1_RXD6_GPIO4_IO8    0x16
                        >;
                };
LEDs
If any LEDs are connected to GPIOs, you have the possibility to access them by a special LED driver interface instead of the general GPIO interface (section GPIOs). You can then access them using /sys/class/leds/ instead of /sys/class/gpio/. The maximum brightness of the LEDs can be read from the max_brightness file. The brightness file will set the brightness of the LED (taking a value from 0 up to max_brightness). Most LEDs do not have hardware brightness support and will just be turned on by all non-zero brightness settings.

Below is a simple example:

To get all LEDs available, type:
target$ ls /sys/class/leds
led-blue@  led-green@ led-red@   mmc0::@    mmc1::@    user-led1@ user-led2@ 
Here the LEDsuser-led1 and user-led2 are on the expansion board PEB-EVAL-01 and the others are on phyBOARD-Polaris.

To toggle the LEDs ON, use:
target$ echo 255 > /sys/class/leds/user-led1/brightness
To toggle OFF:
target$ echo 0 > /sys/class/leds/user-led1/brightness
User I/O configuration in device tree file can be found here: https://git.phytec.de/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mq-phyboard-polaris.dtsi?h=v5.4.70_2.3.2-phy2#n17

User I/O configuration in device tree file can be found here:https://git.phytec.de/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mq-phyboard-polaris-peb-eval-01.dtsi?h=v5.4.70_2.3.2-phy2#n28

Command test:

LED brightness adjustment,

To toggle the LEDs ON, use:
target$ echo 255 > /sys/class/leds/user-led1/brightness
To toggle OFF:
target$ echo 0 > /sys/class/leds/user-led1/brightness

cat /sys/class/leds/user-led1/brightness //Get the current brightness value

video:

lugl4313820

Thanks for sharing the use of GPIO basic peripherals, and I look forward to continued excitement!