User Guide XB1 COM Express Module

Watchdog/Reset

The XB1 COM Express Module is provided with two supervisor circuits to monitor the supply voltages 1.8V, 3.3V, 5V, and to generate a clean power-on reset signal. The healthy state of the XB1 COM Express Module immideately after a reset is signalled by the LED PG (Power Good), indicating that all power voltages are within their specifications and the reset signal has been deasserted.

An important reliability feature is the watchdog function, which is programmable by software. The behaviour of the watchdog is defined within the PLD, which activates/deactivates the watchdog and controls its time-out period. The time-out delay is adjustable in the steps 2, 10, 50 and 255 seconds. After alerting the WD and programming the time-out value, the related software (e.g. application program) must trigger the watchdog periodically. All watchdog related functions are made available by calling service requests within the BIOS.

The watchdog is in a passive state after a system reset. There is no need to trigger it at boot time. The watchdog is activated on the first trigger request. If the duration between two trigger requests exceeds the programmed period, the watchdog times out and a system reset will be generated. The watchdog remains in its active state until the next system reset. There is no way to disable it once it had been put on alert, whwereas it is possible to reprogram its time-out value at any time.

PG (Power Good) LED

The XB1 COM Express Module offers a software programmable LED located. After system reset, this LED defaults to signal the board healthy respectively power good. By the first setting of the GPO20 of the ICH6 this LED changes its function and is then controlled only by the level of the GPO20 pin. Setting this pin to 1 will switch on the LED. The PG LED remains in the programmable state until the next system reset.

GP (General Purpose) LED

A second, programmable LED can be also observed from the front panel. The status of the GP LED is controlled by the GPO18 output of the ICH6. Setting this pin to 1 will switch on the LED. As of current, the GP LED is not dedicated to any particular hardware or firmware function (this may change in the future).

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Intel 82600 manual Watchdog/Reset, PG Power Good LED, GP General Purpose LED