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Watchdog board boasts status monitoring and control

Jul 8, 2009 — by Eric Brown — from the LinuxDevices Archive — 2 views

Acces I/O is shipping three Linux-ready, PC/104-Plus watchdog timer boards designed to monitor system failures. The P104-WDG-E, P104-WDG-CSM, and P104-WDG-CSMA boards offer progressively more advanced features, with the two CSM (Computer Status Monitor) versions adding computer health monitoring and control features, says the company.

The base-level P104-WDG-E board contains a programmable watchdog timer used to monitor application program and operating system performance, says Acces I/O. The board's open collector outputs can also initiate a system reset in case of a lockup, as long as the application software incorporates embedded watchdog software code to communicate a prompt to the timer.

If the prompt is missed, a hard computer reset is initiated after the watchdog timer period has been reached, says Acces. This is said to be useful when the lockup is due to a software loop that hardware watchdogs cannot detect.

The P104-WDG-CSM and -CSMA models add features including voltage monitoring of the PCI-Bus and the ±12V power supply, triggering a response at any 6 percent variation. They also offer temperature monitoring by comparing an on-board sensor output to a preset reference of approximately 50 deg. C. The temperature measurement circuit uses an on-board 8-bit A/D digitizer.


(Click to enlarge)

Other -CSM and -CSMA features include dual digital isolated outputs for controlling or switching external events in response to CSM conditions, says Acces. Two non-isolated digital outputs are said to operate in parallel to these, and can drive LEDs or else output information to another device.

A fused 5V external power pin can bias external LEDs when used with non-isolated digital outputs. A push button reset input is also said to be available.

The top-of-the-line P104-WDG-CSMA model adds two more undedicated 8-bit A/Ds with a 0-5V range that can be used to measure parameters such as battery voltage or humidity, says the company. In addition, fan speed control can be used in conjunction with this model to maintain internal temperatures, and the fan power duty cycle (+12V) is pulse-width modulated to accelerate fan motion when temperature increases.

P104-WDG-CSM block diagram

(Click to enlarge)

The CSMA model also adds a security light sensor used to detect if the enclosure is opened, and it offers an external remote reset through a dedicated opto-isolated digital input to enable a reset based on any transition between 3-18V. The reset can be triggered remotely from an RS-232 signal transition.

The CSMA board is also said to offer additional fused 5V and 12V pins for powering external circuitry or devices. An option enables the board to be added to the top of a PCI-104 express stack without mechanical interference, says the company.

Acces did not reveal the component sources for its board. However, judging from the photo, there appears to be a Xilinx Spartan XC series field-programmable gate array (FPGA), as well as a PLX PCI chip. Features and specifications listed for the high-end P104-WDG-CSMA include:

  • PC/104 Plus Watchdog Timer:
    • Software selectable timeout from 4 µsec
    • 2.08MHz clock, derived from computer clock (33 MHz ÷ 16)
    • 8-Bit I/O mapped address
  • Watchdog open collector reset outputs
  • Temperature sensor with calibration pot
  • Temperature monitor / alarm
  • Temperature measurement with 8-bit A/D
  • Fan status and speed control
  • PCI/104 power monitor / limit alarm interrupt
  • Opto-isolated input to trigger reset
  • General-purpose opto-isolated input
  • 2 x isolated outputs, current limited
  • TTL reset pushbutton input
  • 2 x general purpose 8-bit A/D inputs
  • External fused 5V and 12V power
  • Light sensor for enclosure security
  • PC/104 bus pass-through connector
  • 32 to 158 deg. F (0 to 70 deg. C) operating temp.; optional -40 to 185 deg. F (-40 to 85 deg. C)
  • +5VDC @ 125mA typical power
  • Linux, Windows, and DOS support

The P104-WDG boards all ship with sample programs and source code in "C" and Pascal for DOS, and Visual Basic, Delphi and Visual C++ for Windows. Linux support consists of installation files and basic samples for programming from user level using an open source kernel driver, says Acces. Third party support for the watchdog timer is said to be provided via a standard dll interface.

NANO I/O Server CD

In September, 2007, Acces I/O announced a tiny embedded system called the NANO I/O Server CD (pictured above). The 4.7 x 4.7 inch computer incorporates the company's ETX-NANO-104 baseboard, combining an ETX processor module with PC/104-Plus expansion.


The P104-WDG watchdog boards are available now, says Acces I/O, for $150 (WDG-E), $190 (WDG-CSM), and $250 (WDG-CSMA). More information may be found here.

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