Owfs has multiple aspects to error management.

Reporting

Logging

Error detection

• 1-wire is an inherently noisy and error-prone protocol.

  • Some adapters improve signal analysis a offer active pull-up
  • Reflections in the line are very sensitive to wiring topology
• OWFS implements all data-correction algorithms (CRC8, CRC16, read after write)
• The internal representation of the 1-wire bus is cached only transiently, so bad information will time out.
• "Uncached" information

Retries

Reconnection

• Background

  • Long-running monitoring processes require resilience
  • It is not unusual for USB (and possibly serial) connections to be transiently disconnected or at least reset
  • The goal is for adapter problems to repair themselves, possibly with a short loss of function

• Implementation

  • Error on 1-wire RESET increment an adapter-specific counter.
  • Any successful RESET resets the counter as well.
  • After an error threshold is passed (currently 5) reconection is attempted.

  • Before any of the major OWFS entry points (read, write, parse, directory) reconnection is attempted

    • The port is formally closed
    • The port is reopened with the same initial specification.

• USB Specifics

  • The USB adapter, DS9490, poses a special problem.
  • USB ports are re-enumerated on reconnection and so using the same "address" doesn't work.
  • OWFS attempts to find a characteristic element on the bus the first time connection is established (one of the *81 chips) and matches that to the available USB adapters on reconnection.

• Exceptions

  • Network connection to owserver does not reconnect. Each transaction has a time limit (2-3 seconds) and then returns an error. Connections in owserver are torn down and restarted with each transaction so reconnection would be superfluous.
  • Network connection to LinkE does trigger the reconnection algorithm.