KB81333
Published: October 5, 2011
Revision: 1.0

Serial I/O may lock up SNAP PAC controller


Applies To:

SNAP-PAC-S1
SNAP-PAC-S2
SNAP-PAC-S1-W
SNAP-PAC-S2-W
SNAP-PAC-R1
SNAP-PAC-R2
SNAP-PAC-R1-W
SNAP-PAC-R2-W

Versions Affected:

Problem was discovered in version: Firmware R9.1b
Problem is fixed in version: Firmware R9.1c

Resolved In Version:

Problem is fixed in version: Firmware R9.1c


Symptoms:

If multiple charts are talking to serial I/O, and one or more of those charts is suspended by the strategy, that chart may be suspended while holding a locked I/O unit. If the host task attempts to talk to that I/O unit, it will effectively lock up host communications. If the chart that continues the suspended chart also talks to the locked I/O unit, it may also be suspended. Example:

  1. Charts A and B talk to I/O unit
  2. Chart A acquires I/O unit 1
  3. Chart B suspends chart A, while A still holds I/O unit 1
  4. Chart B attempts to talk to I/O unit 1; since it is locked, Chart B suspends
Since chart A is started by chart B, and chart B is suspended, waiting for the I/O unit held by chart A, deadlock occurs, locking up both tasks. If the host then attempts to talk to the I/O unit, it will also pause indefinitely, requiring a power cycle to fix the problem.

Workaround:

Use synchronization variables to disallow the suspension of a chart while it accesses a serial I/O unit.

Resolution:

Opto 22 has resolved this issue.

Questions?

Contact: Opto 22 Product Support.
Phone: 800-835-6786 or 951-695-3080
Email: support@opto22.com


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