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USB Debug Techniques
This page outlines the common techniques to debug USB. Each section includes a link to the details.
Contents
sysfs[edit]
The sysfs entry for enumerated USB devices is /sys/bus/usb/devices/.
root@am335x-evm:~# ls /sys/bus/usb/devices/ 1-0:1.0 1-1 1-1:1.0 2-0:1.0 usb1 usb2
Each entry includes all the information about its USB device. The names that begins with usb refer to the USB controllers.
x-0:1.0 is a special case, which refers to the root hub's interface. The devices are named as
- bus-port.port.port
The interfaces follow in the form of
- :config.interface
Details:
debugfs[edit]
/sys/kernel/debug/usb/ |-- devices `-- usbmon
- devices: List of the devices enumerated on the bus with topology information.
- Details:
- <kernel source>/Documentation/us/proc_usb_info.txt
- usbmon: to capture USB traces on the BUS.
- Details:
- <kernel source>/Documentation/us/usbmon.txt
/sys/kernel/debug/<controller>/ |-- regdump |-- testmode |-- mode*: host, device, or otg `-- link_state*: speed
- *: only available in DWC3, not in MUSB.
Dymanic Debug Interface[edit]
Runtime turning on/off the kernel debug statements of dev_dbg() or dev_vdbg(). This interface is not limited to USB, it can be used to debug any driver which is ported to dev_dbg() framework.
Details:
- <kernel source>/Documentation/dynamic-debug-howto.txt
Ftrace[edit]
Ftrace is part of kernel tracing infrastructure which has zero overhead when disabled and minimal overhead when enabled. It is a very useful tool to debug USB issues.
Details:
- <kernel source>/Documentation/trace/ftrace.txt
Tracepints[edit]
Another tool in kernel tracing infrastructure for kernel debugging and performance diagnosis.
Details:
- <kernel source>/Documentation/trace/tracepoints.txt
USB protocol analyzer[edit]
A USB protocol analyzer is a USB bus sniffer which captures, decodes, filters and display USB bus activities.
Gadget Zero[edit]
Gadget Zero is a simple USB gadget driver that is useful for testing controller drivers. It implements two configurations, one for source/sink, the other for loopback. As of in 3.12 kernel, gadget Zero supports Control, Bulk and Isochronous transfers. The kernel community is working on implementing Interrupt transfer support.
Details:
Archived[edit]
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