ONDA SOM/ONDA Hardware/Peripherals/Watchdog
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| 2026/03/16 | First documentation release | ||
Contents
Watchdog[edit | edit source]
An external watchdog timer (WDT), Maxim MAX6373, WDO output signal is connected to the PS_POR_B signal. During normal operation, the microprocessor should repeatedly toggle the watchdog input WDI before the selected watchdog timeout period elapses to demonstrate that the system is processing code properly. If the μP does not provide a valid watchdog input transition before the timeout period expires, the supervisor asserts a watchdog (WDO) output to signal that the system is not executing the desired instructions within the expected time frame. The watchdog output pulse is used to reset the μP.
Default configuration[edit | edit source]
MAX6373 timeout is pin-selectable. It can be configured through the WDT_SET0, WDT_SET1 and WDT_SET2 signals. By default, they are configured as follows:
- WD_SET2 = 0
- WD_SET1 = 1
- WD_SET0 = 1
This set selects the option disabled(the exhaustive list of configurations options is descripted on MAX6373 page 4 datasheet):
Watchdog signals[edit | edit source]
Watchdog signals are connected to the pinout connector (J2 and J3) on ONDA.
| Pin# | Pin name | Function | Notes |
|---|---|---|---|
| J2.96 | WDT_SET2 | SET2 | Internal 10K Ω pull-down |
| J2.98 | WDT_SET1 | SET1 | Internal 10K Ω pull-up |
| J2.100 | WDT_SET0 | SET0 | Internal 10K Ω pull-up |
| J3.100 | WDT_REARM | WDI | Internal 10K Ω pull-down |
| J2.114 | PS_POR_B | WDO | For further details, please refer to Reset_scheme_and_control_signals
WDO can be optionally connected to the MRSTn signal (J2.116 pin) |
When the watchdog is started, the software (bootloader/operating system) must take care of toggling the watchdog trigger pin (WDI) before the timeout expiration.
Selecting different configurations[edit | edit source]
Since WD_SETx signals are routed externally, WDT configuration can be changed by optional circuitry implemented on the carrier board. Different solutions can be implemented on the carrier board, depending on system requirements. The easiest circuit consists of additional stronger pull-up/down resistors connected to WDT_SETx pins in order to overrule default configuration. As MAX6373 allows to change the configuration during operation, more complex solutions can be implemented as well.
