On Jun 16, 2014, at 10:41 PM, Gupta, Pekon wrote: > Hi Larry, > >> From: Wolfgang Denk >>> In message <ba...@usgs.gov> 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. >> > > The fix and issue is given in the same mail as provided by you > ... > "I think we've found an issue. As I already mentioned, when an FTDI cable is > connected everything works fine. First we thought it could be a grounding > problem, but we couldn't found anything. Afterwards we had only the TX and > GND signal of the FTDI cable connected, so we could see what the BB sends. We > found out, that the BB goes into the U-Boot mode (the mode where you have to > hit a key shortly after power up). It seems like that the BB receives > something over the RX signal of the FTDI. We think the problem is the pull > down resistor of the RX signal. We have changed it to a pull up, since the > idle state of the UART is 3.3V, and changed the resistor to 10k instead of > 100k. Now everything works fine. > > Regards, > duckhunter" > ... > There are other responses too on same mail-thread which you can explore. >
I experience the unrequested U-Boot prompt even when the FTDI cable is attached. I saw many suggestions for fixes on various web pages, and none of them seemed to work for everyone that tried them. The fix to slightly harden U-Boot's behavior worked. I agree completely with Wolfgang's opinion about either the design or quality of the hardware. Is this a lower quality hobbyist device? Perhaps. It is also affordable, very popular, and very useful. This is a dedicated (~TTL, not RS-232) console port, not typically exposed to the user of the device, whose sole purpose is to interact directly with the embedded U-Boot and Linux. Is it really such a good thing that U-Boot is so promiscuous in what it is willing to accept as an invitation to converse? I think it is good defensive programming to be a bit pickier. What is the harm? I do not wish to argue with anyone about it. I can make the change for myself and I will certainly document the reason I am making the change in my notes. Thank you for your suggestions. Larry Baker US Geological Survey 650-329-5608 ba...@usgs.gov > with regards, pekon _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
