The serial-port interface

The serial-port interface enables input and output access to a specific serial port on a device typically running Ubuntu Core. As a result, and because it provides such privileged access to configure serial port hardware, serial-port is considered a restricted interface.

Use snap interface serial-port to see which serial-port devices are available on the system:

$ snap interface serial-port 
name:    serial-port
summary: allows accessing a specific serial port
slots:
  - core:model01 (allows accessing a specific serial port)
  - core:monome (allows accessing a specific serial port)

Once connected, the consuming snap can use the device via the path specified by the connected slot.

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Developer details

Auto-Connect: no
Attributes:

• Should specify a single path attribute:
  • path (slot): path to serial device node e.g. /dev/ttyS1

• Or three attributes:
  • usb-vendor (slot): integer representing the USB Vendor ID, must be in range 0 < vid <= 65535
  • usb-product (slot): integer representing the USB Product ID, must be in range 0 <= vid <= 65535
  • path (slot): path of the form /dev/serial-port-... where a symlink will be created to the device e.g. /dev/serial-port-mydevice

Hardware IO interfaces covers some general considerations common to these kinds of devices.

To use a serial-port device, the snap developer must add plugs: [ serial-port ] to a snap’s snapcraft.yaml. The snap user can then access a specific serial-port device with an interface connection.

Code examples

The following example shows the slot configuration, such as from the gadget snap, and includes which snaps are permitted to connect automatically:

serial-port:
    allow-auto-connection:
      -
        on-store:
          - (whatever)
        plug-names:
          - serial-foo
        plug-snap-id:
          - foooVbn5YriRw2sRVw7Cuj5PbjJjwnFb
        slot-attributes:
          path: /dev/whatever
        slot-names:
          - serial-foo

All attributes must match for an auto-connection attempt to be successful. The above example requires a connecting snap to have a matching snap-id and plug name. For example, the following snapcraft.yaml stanza for the connecting snap would not connect:

apps:
  whatever:
     plugs:
        serial-port

While the following snapcraft.yaml stanza for the connecting snap would automatically connect:

apps:
  whatever:
     plugs:
        serial-foo
plugs:
   serial-foo:
      interface: serial-port

The test code can be found in the snapd repository: serial_port_test.go.

The source code for the interface is in the snapd repository: serial_port.go

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Last updated 2 years ago.