Expansion Header (GPIO/SPI/I2C/UART/SWR/I2S)¶

The MitySOM-QC6490 devkit has 2 expansion headers, J21 and J22, located on the bottom side of the PCB.

Several peripheral interfaces are available via these expansion headers.

To see which interfaces are available on each pin, refer to the MitySOM-QC6490 Development Kit Datasheet and the MitySOM-QC6490 DataSheet

Development Board Configuration¶

Ensure that Switch S10 is set properly.

• Switch 1 should be set to enable the 1V8 expansion supply from the DC supply
• Switch 2 should not be set to disable the 1V8 expansion supply from the SOM
• Switch 3 should be set to enable the 3V3 expansion supply from the DC supply
• Switch 4 should NOT be set for Rev 1 or 2 of the Development Board as 3.3V from the SOM may actually be a higher volage. See MitySOM-QC6490 Development Kit Datasheet for further details

GPIO Control¶

libgpiod¶

The libgpiod tool is the recommended way to control and monitor pins configured as GPIO. There are bindings for C++ and other high-level languages, as well as command line tools like gpioget and gpioset.

Note: libgpiod is currently not persistent, meaning that any pin states that were modified are not guaranteed to remain in the same state after program execution finishes.

• The gpioinfo command will print out the all of the GPIO pins, including the names for pins that have them assigned. All of the GPIO pins on the expansion headers have names assigned.

• The gpioset command can be used to set pins to output high or low, for example: set GPIO_16 high with gpioset GPIO_16=1.
  Line bias can be set with the -b option, Ex: gpioset -b pull-up GPIO_16=1
  The command can be run with with the -z option to run it as a background process and keep it active: gpioset -z GPIO_16=1
  Note: the gpioset utility is not persistent, meaning that the assingment only remains in effect for as long as the gpioset process is active. libgpiod is currently adding support for persistence via the gpio-manager user space daemon.

• The gpioget command can be used to set pins to input and read their value, ex: read GPIO_16 gpioget GPIO_16
  In order to read the value without changing the pin to input, use the -a option.

• gpiomon will set the pin to input and print edge events as they are detected.

• gpiodetect will print out the gpiochip info, the chip numbers refer to the following units:

  gpiochip	IC
  0	PM7250B
  1	PM7325
  2	PM7350C
  3	PMK7325
  4	QC6490
  5	LPASS LPI TLMM

More info on the libgpiod command-line tools can be found here.

sysfs¶

Alternatively, the legacy sysfs method can still be used with to control the GPIO pins (with persistence).
Details of user-level access are given in https://www.kernel.org/doc/Documentation/gpio/sysfs.txt. What follows is a brief sampling of what can be done.

You can print GPIO info, including the index of the desired pin, by mounting debugfs:mount -t debugfs none /sys/kernel/debug, and reading /sys/kernel/debug/gpio.
Note: The GPIO line names are not shown in this file, but it can be cross referenced with the output of gpioinfo to determine the index of the desired pin.

Assume we want to access the GPIO at index 563.

• Making the GPIO accessible from user-space.
  

  echo 563 >/sys/class/gpio/export
  

• Input GPIOs
  • Setting the direction of the GPIO for input
    

    echo in >/sys/class/gpio/gpio563/direction
    

  • See the current value
    

    cat /sys/class/gpio/gpio563/value
    

• Output GPIOs
  • Setting the direction of the GPIO for output
    

    echo out >/sys/class/gpio/gpio563/direction
    echo high >/sys/class/gpio/gpio563/direction  # sets direction and initial value
    echo low >/sys/class/gpio/gpio563/direction
    

  • See the current value
    

    cat /sys/class/gpio/gpio563/value
    

  • Set the current value
    

    echo 1 >/sys/class/gpio/gpio563/value
    

• Checking the direction
  

  cat /sys/class/gpio/gpio563/direction
  

• Stopping access from user-level
  

  echo 563 >/sys/class/gpio/unexport
  

Reconfiguring the QUP pins¶

WIP. Configuring the QUP pins for functions other than GPIO requires rebuilding the Trust Zone firmware and will be detailed in the future.

Enabling the RTC clocks¶

WIP. Enabling the RTC clocks on J22 pins 5 and 19 requires rebuilding the firmware and will be detailed in the future.

Using the SMB pins for an additional charge pump IC.¶

WIP. Details on using the SMB will be provided in the future.

Using the EXP power pins¶

The 1V8-EXP and 3V3-EXP pins provide power output on the expansion header. The power rail source can be configured to either come from the devkit baseboard power output (e.g. 1V8-DC), or the SOM power output (e.g. 1V8-SOM).
This is configurable by either hardware or software, with software control taking precedence. For more information on power output, reference the MitySOM-QC6490 Developmnet Kit Datasheet.

Hardware control example:

1. Enable the 1V8-EXP power output by setting the DIP switch S10-1 to the ON position.
2. Change the 1V8-EXP power source to 1V8-SOM by setting the DIP switch S10-2 to the ON position. (The 1V8-DC power source is selected by setting it to the OFF position).

Software control example:

1. Enable the 1V8-EXP power output by setting the 1V8-EXP-EN GPIO pin to HIGH:
   

   gpioset -z 1V8-EXP-EN=1
   

2. Change the 1V8-EXP power source to 1V8-SOM by setting the 1V8-EXP-SOM GPIO pin to HIGH:
   

   gpioset -z 1V8-EXP-SOM=1
   

   (The 1V8-DC power source is selected by setting it LOW).