102 lines
3.9 KiB
Plaintext
102 lines
3.9 KiB
Plaintext
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Mini-HOWTO for using the earlyprintk=dbgp boot option with a
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USB2 Debug port key and a debug cable, on x86 systems.
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You need two computers, the 'USB debug key' special gadget and
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and two USB cables, connected like this:
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[host/target] <-------> [USB debug key] <-------> [client/console]
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1. There are three specific hardware requirements:
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a.) Host/target system needs to have USB debug port capability.
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You can check this capability by looking at a 'Debug port' bit in
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the lspci -vvv output:
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# lspci -vvv
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...
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00:1d.7 USB Controller: Intel Corporation 82801H (ICH8 Family) USB2 EHCI Controller #1 (rev 03) (prog-if 20 [EHCI])
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Subsystem: Lenovo ThinkPad T61
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Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
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Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
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Latency: 0
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Interrupt: pin D routed to IRQ 19
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Region 0: Memory at fe227000 (32-bit, non-prefetchable) [size=1K]
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Capabilities: [50] Power Management version 2
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Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
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Status: D0 PME-Enable- DSel=0 DScale=0 PME+
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Capabilities: [58] Debug port: BAR=1 offset=00a0
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^^^^^^^^^^^ <==================== [ HERE ]
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Kernel driver in use: ehci_hcd
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Kernel modules: ehci-hcd
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...
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( If your system does not list a debug port capability then you probably
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wont be able to use the USB debug key. )
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b.) You also need a Netchip USB debug cable/key:
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http://www.plxtech.com/products/NET2000/NET20DC/default.asp
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This is a small blue plastic connector with two USB connections,
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it draws power from its USB connections.
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c.) Thirdly, you need a second client/console system with a regular USB port.
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2. Software requirements:
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a.) On the host/target system:
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You need to enable the following kernel config option:
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CONFIG_EARLY_PRINTK_DBGP=y
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And you need to add the boot command line: "earlyprintk=dbgp".
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(If you are using Grub, append it to the 'kernel' line in
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/etc/grub.conf)
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NOTE: normally earlyprintk console gets turned off once the
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regular console is alive - use "earlyprintk=dbgp,keep" to keep
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this channel open beyond early bootup. This can be useful for
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debugging crashes under Xorg, etc.
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b.) On the client/console system:
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You should enable the following kernel config option:
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CONFIG_USB_SERIAL_DEBUG=y
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On the next bootup with the modified kernel you should
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get a /dev/ttyUSBx device(s).
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Now this channel of kernel messages is ready to be used: start
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your favorite terminal emulator (minicom, etc.) and set
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it up to use /dev/ttyUSB0 - or use a raw 'cat /dev/ttyUSBx' to
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see the raw output.
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c.) On Nvidia Southbridge based systems: the kernel will try to probe
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and find out which port has debug device connected.
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3. Testing that it works fine:
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You can test the output by using earlyprintk=dbgp,keep and provoking
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kernel messages on the host/target system. You can provoke a harmless
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kernel message by for example doing:
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echo h > /proc/sysrq-trigger
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On the host/target system you should see this help line in "dmesg" output:
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SysRq : HELP : loglevel(0-9) reBoot Crashdump terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) saK show-backtrace-all-active-cpus(L) show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount show-blocked-tasks(W) dump-ftrace-buffer(Z)
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On the client/console system do:
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cat /dev/ttyUSB0
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And you should see the help line above displayed shortly after you've
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provoked it on the host system.
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If it does not work then please ask about it on the linux-kernel@vger.kernel.org
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mailing list or contact the x86 maintainers.
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