Date: Wed, 22 Nov 2017 09:33:22 +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: <5c6da274-102c-33c6-50f0-20597cf8e7ef@selasky.org> In-Reply-To: <36165883-5cb7-aabc-c81e-cb5458029803@freebsd.org> References: <11ce9826-f768-3ea0-547d-2d182d1552f0@gmail.com> <36165883-5cb7-aabc-c81e-cb5458029803@freebsd.org>
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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 --HPS
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