GPIOs on Astra Machina

Astra Machina integrates many GPIOs to support its various functionalities. This guide will cover how to use GPIOs with Astra Machina and configure their functionality.

On Astra Machina:

• All of the GPIOs are multiplexed and can be configured for different functionality.

• All GPIOs can be assigned interrupts. However, GPO (output only pins) cannot.

Specific details on GPIOs can be found in the Astra Machina Eval Platform.

Accessing GPIOs from Userspace

GPIOs can be accessed and configured using the libgpiod tools. These tools interface with the kernel’s character device interface /dev/gpiochipN instead of the deprecated sysfs interface.

To identify available GPIO chips and lines, use:

root@sl1680:~# gpiodetect
root@sl1680:~# gpioinfo

GPIOs are accessed by chip and line offset, rather than the legacy global GPIO number.

For example, GPIO[36] on the SL1680 corresponds to line offset 4 on its GPIO controller (see GPIO Mappings).

To read the value of GPIO[36]:

root@sl1680:~# gpioget -c gpiochip1 4
"4"=active

To configure GPIO[36] as an output and set it high. The command will hold the line high until it exits.

root@sl1680:~# gpioset -c gpiochip1 4=1

To set GPIO[36] low. The command will hold the line low until it exits.

root@sl1680:~# gpioset -c gpiochip1 4=0

The libgpiod tools support input and output. The gpioget program requests the line as an input whereas gpioset requests the line as an output. The line is released automatically when the command exits.

Note

Unlike the legacy sysfs interface, the GPIO value is only driven while the process holds the line. When gpioset exits, the line is released and its state is no longer guaranteed. Run gpioset in the background to hold the line while working with gpios.

Changing the Function of GPIOs

GPIOs which are assigned to other functionality can be reconfigured to function as generic GPIOs. This is done by updating the device tree entries in the Linux Kernel. This requires modifying the linux-syna package using devtool:

devtool modify linux-syna

Modify the platform dts file located in build-sl1680/workspace/sources/linux-syna/arch/arm64/boot/dts/synaptics.

	SL1620	SL1640	SL1680	SL261x
DTS	myna2-rdk.dts	platypus-rdk.dts	dolphin-rdk.dts	sl261*-rdk.dts

First, identify where the GPIOs are currently configured in the dts file and disable them. Then reassign them to function as GPIOs.

The following example will reassign GPIO[12] and GPIO[13] to function as GPIOs in SL1620.

Build the image with the updated device tree entries:

devtool build linux-syna
devtool build-image astra-media

GPIO Mappings

Userspace GPIO IDs are assigned based on the gpiochip number which is assigned dynamically. Changes in the device configuration, such as updating the device tree (DTS), can cause the gpiochip number to change. Therefore, userspace GPIO IDs need to be calculated using the current gpiochip number assigned to the GPIO port.

GPIOs 0 - 31:

\[\text{GPIO ID} = \text{gpiochip#} + \text{GPIO#}\]

GPIOs 32 - 63:

\[\text{GPIO ID} = \text{gpiochip#} + (\text{GPIO#} - 32)\]

GPIOs 64 - 95:

\[\text{GPIO ID} = \text{gpiochip#} + (\text{GPIO#} - 64)\]

To do this calculation start by identifying the gpiochip number for the controller on which the GPIO is attached. The address will match the GPIO ports in the tables below. Find which gpiochip is associated with which GPIO port by running gpiodetect. The output will contain the GPIO port address of the port associated with the gpiochip.

gpiochip numbers on SL1680

The following examples show how to calculate GPIO IDs for various GPIOs. Using the gpiochip number associated with the GPIO port.

Calculate GPIO[5]:

\[\text{GPIO[5]} = 416 + 5 = 421\]

Calculate GPIO[46]:

\[\text{GPIO[46]} = 480 + (46 - 32) = 494\]

Calculate GPIO[80]:

\[\text{GPIO[80]} = 448 + (80 - 64) = 464\]

SL1620

GPIO Port	Address	GPIOs
gpio@0800	f7e80800	0 to 31
gpio@0c00	f7e80c00	32 to 63
gpio@1000	f7e81000	64 to 95

SL1640 / SL1680

GPIO Port	Address	GPIOs
gpio@2400	f7e82400	0 to 31
gpio@0800	f7e80800	32 to 63
gpio@0c00	f7e80c00	64 to 95

SL261x

GPIO Port	Address	GPIOs
gpio@7000	f7f07000	0 to 31
gpio@e000	f7f0e000	32 to 63
gpio@8000	e5038000	64 to 79
gpio@9000	e5039000	80 to 87
gpio@a000	e503a000	88 to 95

Note

Mappings may change if based on modifications to devicetree. The tables above are for reference only and my not be accurate for all configurations.