Description

The Freescale MCF5272 ColdFire processor has a built-in watchdog device. Once started it will automatically reset the processor unless software updates the device at regular intervals. The package CYGPKG_DEVS_WATCHDOG_MCF5272provides an eCos driver for this device, complementing the generic package CYGPKG_IO_WATCHDOG. The functionality should be accessed via the standard eCos watchdog functions watchdog_start, watchdog_reset and watchdog_get_resolution.

The watchdog driver only supports reset mode. The hardware can also be configured to raise an interrupt when the watchdog times out, but this mode of operation is not supported.

Configuration Options

The MCF5272 watchdog driver package should be loaded automatically when selecting a platform containing an MCF5272 processor, and it should never be necessary to load it explicitly into the configuration. The package is inactive unless the generic watchdog support CYGPKG_IO_WATCHDOG is loaded. Depending on the choice of eCos template it may be necessary to load the latter.

The package provides two main configuration options. CYGIMP_WATCHDOG_HARDWARE can be used to disable the use of the hardware watchdog and switch to a software emulation provided by the generic watchdog package instead. This may prove useful during debugging. CYGNUM_DEVS_WATCHDOG_MCF5272_TICKS determines the timeout before the hardware watchdog resets the processor. It should be a 15-bit number, with each tick corresponding to 32768 system clock cycles. For a processor operating at 66MHz each tick is approximately 0.5 milliseconds so the default value of 2000 corresponds to a one-second timeout. The maximum value of 32767 gives a timeout of approximately 16 seconds.

Porting

The watchdog device driver does not require any platform-specific support. The only porting effort required is to list CYGPKG_DEVS_WATCHDOG_MCF5272 as one of the hardware packages in the ecos.db target entry.