Date: Thu, 23 Nov 2017 23:16:16 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Julian Elischer <julian@freebsd.org>, Farhan Khan <khanzf@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: Is ddb(4) over a USB-to-Serial port possible? Message-ID: <cc2c013c-0e38-5973-2323-5d08c27c2de3@selasky.org> In-Reply-To: <aad5dce5-ae76-f2af-0d1b-3e39e5f9cdfb@freebsd.org> References: <11ce9826-f768-3ea0-547d-2d182d1552f0@gmail.com> <36165883-5cb7-aabc-c81e-cb5458029803@freebsd.org> <5c6da274-102c-33c6-50f0-20597cf8e7ef@selasky.org> <aad5dce5-ae76-f2af-0d1b-3e39e5f9cdfb@freebsd.org>
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On 11/23/17 16:59, Julian Elischer wrote: > On 22/11/17 4:33 pm, Hans Petter Selasky wrote: >> On 11/22/17 08:40, Julian Elischer wrote: >>> On 22/11/17 3:08 pm, Farhan Khan wrote: >>>> Hi all >>>> >>>> I am reading here in section "10.5, On-Line Kernel Debugging User >>>> Remote GDB" that you can run ddb(4) over a serial cable. I am >>>> interested in setting this up. >>>> >>>> My development box does not have a serial port (however, I do see a >>>> uart0 device in the kernel messages), so I attached a USB serial >>>> port attached to a machine with a serial port. The device uses the >>>> uslcom(4) driver and is listed as "Silicon Labs CP2102 USB to UART >>>> Bridge Controller". When I enter ddb and enter "gdb" I receive the >>>> error "The remote GDB backend could not be selected." >>>> >>>> The hint.uart.0.port in /boot/device.hints is still set to 0x3F8, >>>> which corresponds to the aforementioned kernel messages. I am not >>>> certain if this is the same port as the USB-based serial port. Does >>>> this feature work over USB? >>>> >>>> Thanks, >>>> Farhan Khan >>>> _______________________________________________ >>>> freebsd-hackers@freebsd.org mailing list >>>> https://lists.freebsd.org/mailman/listinfo/freebsd-hackers >>>> To unsubscribe, send any mail to >>>> "freebsd-hackers-unsubscribe@freebsd.org" >>>> >>> generally speaking the answer is no, unless the device is emulated >>> using SMI or some other mechanism that is independent of FreeBSD. >>> >>> uart0 is not the device on the USB but a hardware device at 3F8, >>> regardless of whether it actually exists. Since the USB stack is not >>> really functional when in the debugger, it can not be used to >>> communicate with the debugger. >>> >>> I find a better answer is to fire up the test machine under bhyve, in >>> which case its console is accessible through any stream session. >>> (e.g. ssh).. >>> >> >> Hi, >> >> There is another setting for this: >> >> Try setting cons_baud and cons_unit below. USB serial supports polling >> from the debugger after panic. >> >> hw.usb.ucom.cons_baud: 9600 >> hw.usb.ucom.cons_subunit: 0 >> hw.usb.ucom.cons_unit: -1 >> hw.usb.ucom.debug: 0 >> hw.usb.ucom.pps_mode: 0 >> > wow.. I will need to try this when I have the appropriate setup. > is this in the kenv? is it in loader.conf or sysctl.conf? > Hi, /boot/loader.conf or kenv or sysctl Before attaching the device. --HPS
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