sismatic 0.2.15

Blocking Python facade for driving Extron SIS devices over SSH

sismatic

An open-sourced library for working with the Simple Instruction Set used by many Extron devices. The name comes from SIS + automatic, because it handles the SIS machinery behind the scenes without human control.

Why?

There are several reasons why this library is worthwhile:

1. Relies on a stable, unchanging protocol.
2. Hides complexities of managing connections.
3. Hides complexities of byte-level communication.

Crates

• core
• python
• web
• cli

Configuration Example

# Global settings
[defaults]
port = 22023
connect_secs = 5
command_secs = 3
eager = true # eagerly establish connections to pay the cost of the full SSH handshake up front (default: false; connect upon first instruction)
sis_keepalive_secs = 120 # interval at which to send a probe instruction to SMPs to keep connection open; SMPs idle timer is set to 5 minutes by default. (default: 120)

[[device]]
id = "atrium-101"
host = "10.0.0.7"
username = "admin"
password = "extron"

[[device]]
id = "annex-far"
host = "10.0.0.8"
username = "admin"
password = "extron"
connect_secs = 10   # override default connect timeout
command_secs = 8    # override default command timeout

Warm versus Cold Connections

The premise is that the SSH handshakes are expensive, so having a "warm" or preestablished connection is important for runtime responsiveness. Device connections are lazy by default, which means that connection is delayed and first established when first instruction is sent. After a connection is established, the SSH layer will automatically keep the connection alive until the device itself terminates the connection due to inactivity (no instructions sent for some interval). The default interval is 5 minutes on some devices after which the connection will go "cold" again and be reestablished upon the next command. If desired, it is possible to eagerly open connections to devices by settings the eager configuration option. This will enable maximum performance at runtime because it will cause connections to devices to open up front i.e. pay the cost of the full SSH handshake at startup. To keep the connections "warm", there is the sis_keepalive_secs setting, which sets an interval in which a benign instruction is sent to the device to reset the device's inactivity timer periodically.