Dear Larry, In message <5070a944-cc27-4388-91e5-78b0792e5...@usgs.gov> you wrote: > > A recent situation has awakened me to a a behavior of U-Boot that maybe > should be changed.
U-Boot related questions should better be discussed on the U-Boot (rather than the ELDK) mailing list. I'm adding the U-Boot list on Cc. > I am experimenting with a BeagleBone Black (BBB) single-board > computer. Occasionally when I perform a reboot, the BBB never > finishes booting Linux. When I happen to have a console cable > connected, I see the U-Boot prompt. This explains why the BBB has not > booted Linux. But it is a mystery why U-Boot is waiting for a command > when I did not request interrupting the autoboot sequence. > > I found many others reporting the same experience -- and no solution. > Until I found Andrew Glen's 10/28/2013 post at > https://groups.google.com/forum/#!topic/beagleboard/aXv6An1xfqI about > U-Boot hangs likely due to noise on the UART0 port. The solution he > applied was to rebuild U-Boot to require specific text -- "uboot" -- > to interrupt the autoboot sequence. (BBB have no flash, so there is > no opportunity to permanently alter any U-Boot environment variables, > if this is settable.) You should be able to store the environment on SDCard. > It occurs to me that this might be a more common occurrence on any > number of circuit boards. No, this is in no way a common issue. If you have any such line noise on a serial port, you should start looking for hardware (design) problems. This is _not_ normal. IF several boards of a specific brand show such a problem, then I'm willing to bet that it's caused by broken (or simply too cheap) hardware design. No industrial grade board I've ever seen has any such issues. > I have used many ARM single-board computers that have U-Boot. As far > as I recall, they all prompt "Hit any key to stop autoboot:". It is > probably not such a good idea that ANY character can interrupt the > U-Boot autoboot sequence. Perhaps the default should be to require an > unusual character, like F2 or DEL for BIOS. Or a multi-character > sequence within a short period of time, like the "+++" to enter > command mode on the old Hayes modems. U-Boot allows you to do that, if you really need/want to. > As I said, this awakening only occurred to me because of my recent > experience with boot failures. My realization is that U-Boot could > probably do a little better job of protecting our (likely unattended, > embedded) systems with a minimum of change to the code. I plan to > make it my practice to #define CONFIG_AUTOBOOT_DELAY_STR. I'm > thinking that should probably be the default. U-Boot allows you such customization. But I disagree that this should be the default. Actually you are just papering over a hardware problem. Line noise on a serial port that inserts phantom characters is something that should be fixed, not ignored. And on ony well- behaving hardware the problem that bothers you simply does not exist. > Thank you for your valuable contributions (U-Boot and more). You are welcome. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de "We don't have to protect the environment -- the Second Coming is at hand." - James Watt _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot