Date: Sun, 27 Apr 2014 12:30:29 -0600 From: Warner Losh <imp@bsdimp.com> To: Ian Lepore <ian@FreeBSD.org> Cc: Bakul Shah <bakul@bitblocks.com>, FreeBSD ARM <freebsd-arm@FreeBSD.org> Subject: Re: Looking for FreeBSD u-boot/kernel debugging help (BeagleBone Black) Message-ID: <35FCA9EC-1569-494D-B193-90926D802219@bsdimp.com> In-Reply-To: <1398618296.61646.161.camel@revolution.hippie.lan> References: <CADH-AwHN0=p4z0RJZNcoRdoDJTMVAtK5F3TNCh5qdMWessQ0KQ@mail.gmail.com> <20140426233438.49123B827@mail.bitblocks.com> <1398618296.61646.161.camel@revolution.hippie.lan>
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On Apr 27, 2014, at 11:04 AM, Ian Lepore <ian@FreeBSD.org> wrote: > On Sat, 2014-04-26 at 16:34 -0700, Bakul Shah wrote: >> On Sat, 26 Apr 2014 18:29:35 EDT Winston Smith = <smith.winston.101@gmail.com> wrote: >>> I also discovered that if I disconnect = my >>> serial terminal and reconnect it, it seems to bring the FreeBSD = kernel >>> to a debug prompt of sorts -- is there any documentation on this? >>=20 >> I suspect disconnecting/reconnecting the serial cable looks like >> a break to the kernel and that drops it into the debugger "ddb". >> [Though I can't seem to send a real break to it using kermit!] >>=20 >> Type c and hit return to continue.=20 >>=20 >> To disable this behavior I think you can do >> sysctl debug.kbd.break_to_debugger=3D0 >> or add >> debug.kbd.break_to_debugger=3D0 >> to /etc/sysctl.conf >>=20 >> man 1 ddb -- for debugger commands >> man 4 ddb -- for kernel config options to control ddb behavior >=20 > That's exactly correct -- connecting the cable sometimes leads to a > spurious break being asserted on the line (a break is just a long > sequence of zeroes with no start/stop/data bit transitions). >=20 > It's possible to configure a kernel without BREAK_TO_DEBUGGER and with > ALT_BREAK_TO_DEBUGGER. That eliminates most line-noise spurious = breaks > but still allows the <CR> ~ ^b break sequence (which could = theoretically > happen in a burst of line noise, but not likely). A few of our = kernels > have BREAK_TO_DEBUGGER in the config, and I think that's probably a > mistake. Most folks these days don't know anything about breaks or = how > to generate one on purpose. =20 >=20 > Any objections to removing them and using only the safer ALT_BREAK > option? Please leave it in the ATMEL config, but I think you can remove it from = the rest (including the specific atmel SoC boards). Warner=
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