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.

../_images/sl1680-gpiochip-gpiodetect.png — 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

Note

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

SM GPIO Mappings

The System Manager (SM) has its own GPIO controller separate from the SOC GPIOs documented above. SM GPIOs are directly managed by the M52 core running the system manager firmware, but are also accessible from Linux via libgpiod.

Note

SM GPIO pin muxing is controlled by the SM firmware device tree (Zephyr or FreeRTOS side), not the Linux device tree. Changing the function of SM GPIOs requires updating the system manager firmware configuration.

SL1620

The SM GPIO controller on SL1620 supports 12 SM_GPIOs: SM_GPIO[0:11].

Register Block	Address	SM GPIOs
GPIO0	f7e80000	SM_GPIO[0:11]

For SL1620, the SM_GPIO Linux GPIO group maps as follows:

SM GPIOs	Linux GPIO Port
SM_GPIO0 ~ SM_GPIO11	portb 0 ~ 11

SL261x

The SM GPIO controller supports 39 SM_GPIOs: SM_GPIO[0:38].

In the register view, the SM GPIO block is split as:

Register Block	Address	SM GPIOs
GPIO0	e5038000	SM_GPIO[0:15]
GPIO1	e5039000	SM_GPIO[16:23]
GPIO2	e503a000	SM_GPIO[24:31]
GPIO3	e503b000	SM_GPIO[32:38]

For SL261x, the SM_GPIO Linux GPIO groups map as follows:

SM GPIOs	Linux GPIO Port
SM_GPIO0 ~ SM_GPIO15	portc 0 ~ 15
SM_GPIO16 ~ SM_GPIO23	portd 0 ~ 7
SM_GPIO24 ~ SM_GPIO31	porte 0 ~ 7
SM_GPIO32 ~ SM_GPIO38	portf 0 ~ 6

Accessing SM GPIOs from Linux

Use gpiodetect to identify which gpiochip corresponds to each SM GPIO block:

root@sl2619:~# gpiodetect
gpiochip0 [0-0043] (8 lines)
gpiochip1 [0-0044] (8 lines)
gpiochip2 [e5038000.gpio] (16 lines)
gpiochip3 [e5039000.gpio] (8 lines)
gpiochip4 [e503a000.gpio] (8 lines)
gpiochip5 [e503b000.gpio] (8 lines)
gpiochip6 [f7f07000.gpio] (32 lines)
gpiochip7 [f7f0e000.gpio] (32 lines)

In this example:

SM_GPIO[0:15] is on gpiochip2 (e5038000)
SM_GPIO[16:23] is on gpiochip3 (e5039000)
SM_GPIO[24:31] is on gpiochip4 (e503a000)
SM_GPIO[32:38] is on gpiochip5 (e503b000)

To read SM_GPIO5 (line 5 on gpiochip2):

root@sl2619:~# gpioget -c gpiochip2 5

To set SM_GPIO5 high:

root@sl2619:~# gpioset -c gpiochip2 5=1

To read SM_GPIO20 (SM_GPIO[16:23] block, line offset 4 on gpiochip3):

root@sl2619:~# gpioget -c gpiochip3 4

Note

The gpiochip numbers shown above are examples and may differ on your system depending on device tree configuration. Always run gpiodetect to confirm the current chip-to-address mapping before accessing SM GPIOs.

SM GPIO ID Calculation

SM GPIOs follow the same ID calculation as SOC GPIOs. Use the gpiochip base number for the SM GPIO controller block and add the line offset.

SM_GPIO[0:15] (gpiochip2, base depends on system):

\[\text{SM_GPIO ID} = \text{gpiochip2 base} + \text{SM_GPIO#}\]

SM_GPIO[16:23] (gpiochip3):

\[\text{SM_GPIO ID} = \text{gpiochip3 base} + (\text{SM_GPIO#} - 16)\]

SM_GPIO[24:31] (gpiochip4):

\[\text{SM_GPIO ID} = \text{gpiochip4 base} + (\text{SM_GPIO#} - 24)\]

SM_GPIO[32:38] (gpiochip5):

\[\text{SM_GPIO ID} = \text{gpiochip5 base} + (\text{SM_GPIO#} - 32)\]