Date: Thu, 23 Nov 2017 23:59:54 +0800 From: Julian Elischer <julian@freebsd.org> To: Hans Petter Selasky <hps@selasky.org>, Farhan Khan <khanzf@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: Is ddb(4) over a USB-to-Serial port possible? Message-ID: <aad5dce5-ae76-f2af-0d1b-3e39e5f9cdfb@freebsd.org> In-Reply-To: <5c6da274-102c-33c6-50f0-20597cf8e7ef@selasky.org> References: <11ce9826-f768-3ea0-547d-2d182d1552f0@gmail.com> <36165883-5cb7-aabc-c81e-cb5458029803@freebsd.org> <5c6da274-102c-33c6-50f0-20597cf8e7ef@selasky.org>
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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? > > > --HPS >
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