NXP Semiconductors i.MX 6Dual Reference Manual

Contents

ERR006282Chip Errata for the i.MX 6Dual/6Quad and i.MX 6DualPlus/6QuadPlus, Rev. 6.1, 06/2016188 NXP SemiconductorsWorkaround #2:—Program WDOG_ENABLE eFuse to 1 (default = 0):• Users who do not or cannot use SPI/I2C or SATA as a boot source option canuse this option.• The i.MX 6Dual/6Quad contains a watchdog timer which can be activated viafuse whenever the processor enters Serial Downloader mode. The Watchdogtimer begins a 90-second countdown and, if nothing interrupts this process, thepart resets.• For the watchdog timer workaround, on the rare occurrence of a PFD-related(or other) boot failure, the processor’s ROM falls through to SerialDownloader mode. This occurs in either secure boot or nonsecure bootdevices.If the WDOG_ENABLE eFuse has been set to 1, then, on entering SerialDownloader mode, the watchdog begins a fixed 90-second countdown. If noexternal source interrupts this countdown, the watchdog timer expires andresets the part. Because the PFD-related error, if encountered, does not exhibit“memory,” the subsequent boot operates correctly. No software is required toenable this functionality, only the setting of the WDOG_ENABLE eFuse to 1.• This workaround applies for all boot sources except NAND boot (either SLCor MLC). For NAND boot, the user must implement either the SPI, I2C, orSATA workaround, or the external Watchdog workaround in #3 below.• Use the following steps to understand how the watchdog timer will work inyour system:1. The user must not set BOOT_CFG3[2] (Boot Frequencies). Theymust be left at default.2. The user programs the WDOG_ENABLE eFuse to 1. Note this is apermanent fuse setting which means the watchdog will begincountdown upon entering Serial Downloader mode anytime the chipenters this mode and must be stopped by software to prevent reboot.3. The WDOG_ENABLE timer has a fixed 90-second countdown.This countdown cannot be changed in hardware, only via a softwarecommand.• Because it is assumed a boot failure has occurred and the ROMhas dropped into Serial Downloader mode, it is assumed nosoftware is available to reset this 90-second countdown• During the countdown, the unit will continuously poll for aUSB connection on USB OTG1. If no activity is detectedduring the 90-second window, the watchdog expires and theARM core is reset.• If no boot error occurs, then Serial Downloader mode will notbe entered and the Watchdog will not begin its countdown. Onlywhen Serial Downloader mode is entered will the watchdogbegin a countdown.